British DNA Database Mismatch

nahal writes "DNA evidence is extremely compelling to a jury at trial when trying to convict a suspect. In this article at USA Today, the world's largest DNA crime-solving machine, located in Great Britain, mistakenly matched a suspect to a crime in a 1-in-37 million chance. American experts have called it 'mind blowing'."

Comments

Re:juries

[Anonymous Coward]

that evidence COULD have been planted

but you wouldn't know that because you are a racist and not interested in the facts of the case

Re:Statistics and probability

[Anonymous Coward]

nope, if you are found inocent, they HAVE to remove and destroy fingerprints and DNA records, unless you were already in the records, ie you already have a criminal record.

Therefore if you do not have a criminal record your details are not stored in fingerprint or DNA records. They do however want this to be changed i think so that DNA records are not removed.

Woe to BSD (Part 1

[Anonymous Coward]

Woe to BSD (Part 1)

Hello my dear friends
I here must now plea,
For the life of a friend
Whose stories many do not see.

What friend do I speak for?
Who now hardly is seen?
My friend is the great BSD
Now humbled and forgotten and meek.

For how many posts of Linux doth we see?
How many development kernel posts rage forth like the sea?
When no where can be found the great BSD?
For we are 0wned by VA and now pay the fee.

How many of you have this article seen?
Or this or this, or this one revealed.
For nowhere on the front page can BSD be...
For we are 0wned by VA and our coffin here sealed.

I beg you forget not the great BSD
Without which Linux would likely not be,
And though we are now 0wned by a Linux company
I beg you not forget the great BSD.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Simple Probability

[Anonymous Coward]

Lets see:

1 in 37,000,000 has a probability of ~ 2.70 x 10^-8
1-(2.70 x 10^-8) is about: 0.9999999730.
Now we raise that to the 660,000 power since that is how many people are in their database, yielding: (0.9999999730^660000) ~= .982
Which means there is 1-.982 = 1.78% chance that a random person matches someone in their database :p...
Doesn't sound so unlikely to me!

Re:Simple Probability

[maroberts]

This problem is similar to the so called birthday problem i.e. given a number of people n, what is the possibility of two of them sharing the same birthday? If I remember my stats correctly, the result is surprisingly large...

For n=2
364 ways second person could have birthday without matching first
For n=3
363 ways third person can have birthday not matching other two
p(match) = 1-365x364x363/(365^3)
....

when this gets to about 20, p(match) is about 40%!!

The chances of a DNA match amounts to a similar problem, so the stats rapidly build up to an high likelihood of a match after about 20-30 samples.

An Ode to Trolls

[Anonymous Coward]

An Ode to Trolls

Hello my dear friends
I have something to say,
Please gather around me
And hear me this day.

Do you ever wonder what it means to be a troll?
To be laughed at and flamed and written off as cold?
To be hated and dispised and hunted by some,
To be a savior of justice, of liberty and of freedom?

For never was there a more beautiful creature than a troll,
One with great morals and purpose and ideals and goals,
For where ever censorship and injustice and moderation do lie
You can count on TollTroll, Gnulix or The Hot Grits Guy.

We trolls will return justice and freedom to this land,
We fear not the evil of the Moderators hand,
After all look at what we trolls did for freedom on Usenet!
Er, wait a second... ignore that, thats not what I meant :)

So if you have ever wanted to be hated but loved,
If you have ever wished to be kissed and then shoved,
Help us trolls save slashdot from the hell that awaits,
Before VA then Slashdot becomes the property of Bill Gates.

(P.S. See you on the next weekly Troll Day (Tuesday))

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to Troll Day (Part 1)

[Anonymous Coward]

An Ode to Troll Day (Part 1)

Gather round all you friends
For I have something to say,
About a new invention
We call it: Troll Day.

A day of great joy
A great fair to attend,
Where everyone posts trolls
And moderation is dead.

It's not like most holidays
Of which you may have been told,
Since we hold it every Tuesday
And everyone gets stoned.

So now I take the pleasure
to invite you all here,
And remind you of our next Troll Day
Held once a week, not once a year.

(P.S. See you on Tuesday :))

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to Slashdot

[Anonymous Coward]

An Ode to Slashdot

Once upon a time
In a not so far land,
There existed a website
And it was quite grand.

Though not very flashy,
And often quite slow,
It was a wonderful place,
Where many did go.

Then one stormy night
When evil was near,
Moderation was implemented
But not many seemed to care.

Those who hated microsoft
And who held Linux dear,
They all praised moderation...
They had little to fear.

But if ever a voice
Did praise FreeBSD,
It was moderated down
Such posts are all shitty!

And should ever a poster
Disagree with a moderator on a bad day,
Woe to his karma...
Slowly Moderated away.

And woe to the man
Who did not follow the herd,
For a nice feature of moderation
Was that he would never be heard.

What happened to this free forum
Where opposing views often did meet?
Was liberty defeated?
NO! We would not retreat.

Anonymous Coward to the rescue...
The signs of rebelion came soon,
The Jackie Chan posts,
Hot Grits, ascii pr0n, The trollmastahs loom.

With weapons of ascii
and bowls of Hot Grits
Anonymous Coward said
"Enough of this shit!"

Began The Great War
Where many moderators fought and died
But it all was in vain...
Natalie Portman: Naked and Petrified!

The war is not over
There are still battles to fight,
YOU can make a difference
Help us trolls make Slashdot right!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Re:juries

[Anonymous Coward]

But those 167 people with similar DNA are more likely to live near you. If you are British, probably your DNA is closer matched to those of other Brits than to native Brazilians of Asians, etc.

Re:Welcome to the world of statistics . . .

[Anonymous Coward]

Moderate this (previous posting that is).up. It's worth more than the stupid poem posts (so's this one for that matter :)= ).

Does seem to suggest that the British Police are keen to use a poor quality 6-point database to find someone to frame and then not doing a proper test until the poor sod can prove his innocence by another means. (And they can still frame the 'suspect' by careless cross contamination of the tests. Such contamination is very easy to get by accident with PCR (Polymerase chain reaction) tests which use the DNA's ability to replicate itself to increase the quantity of DNA in the sample, so it theoretically only needs one DNA molecule for a test. Avoiding contamination down to the extent of a single molecule is incredibly difficult (OK I know that bit is obvious to many slashdotters) so if you would quite like the cross-contanimation to occur it aint difficult to engineer.

That should certainly improve the crime clear up rate - lock up a load of innocents and call the crimes solved. (Real criminals still walking free). And dodgy labs get more money for all the wonderful work they are doing helping to 'solve' all these crimes - oh look a cash incentive for the labs to say things match when they shouldn't.

Twins?

[Anonymous Coward]

Out of topic.
What would actually happen with identical twins? Twins have an identical set of DNA right? How would anyone know which twin committed the crime?

Re:Twins?

[orpheus]

>The environmental factors are acting all through
>out the identical twins life time to make their
>DNA different. They're know as viruses. Other
>mutagens will also cause even more differences
>over time.

I'm afraid not. Generally mutagenic changes to each cell will be idiosyncratic -- that is they don't change every cell and the cells that are changed are altered differently, so they get washed out as 'noise' in a PCR RFLP.

You are very correct in citing viruses as one of the few agents (mutagens are not at all uncommon) that could cause a highly consistent change in the genome, but they are rarely (never, so far as I know) so consistent that they approach total alteration.

On a PCR-PAGE gel (with an adequate sample, this could result in abberant or extra bands, it should not erase bands that already exist (beecause some unaltered cells remain. therefore twins would definitely register as positives for each other -- though perhaps with some abberrant bands

>Then there is the testing method. The
>electrophersis gel tests used have rather poor
>repeatability.

Maybe they aren't perfect, but they are pretty darn good. I certainly would never call their reproducibility "poor".

The things that produce bad results are well known, and avoidable. But I don't doubt that technician error or carelessness could create real problems

>Sure some things can be done to help make them
>better. I wouldn't accept a match when the
>samples are done on two different machines in
>different labs. Having two different gel
>suppliers also makes a huge difference. The test
>is really only telling you the length of strands
>between markers where the chemicals split the
>strands into segments.

I, too, would want both samples run on adjoining lanes on the same gel (though irreproducibility would be *far, far* more likely to produce false negatives than false positives)

I don't think they still do RFLP on DNA IDs -- but I could be wrong. PCR RFLP would seem the way to go -- a stronger signal with a tiny sample, and many other advantages.

MY NIGHTMARE:

The tired/careless/whatever technician who double-dips (placing/contminating) my DNA in both the "evidence" and "suspect" lane, and creating a match (especially with PCR RFLP

Re:Twins?

[Old Wolf]

More interesting is the case of Siamese twins, joined at the hip or something. One of them commits a serious crime.. but according to US law he cannot be imprisoned because it would not be fair on the other twin!

Although if one got the death penalty, perhaps they could cut one head off or something

Re:Twins?

[Gyver]

I have seen a TV special on DNA testing and in this program they brought up this same question. It's rather late and my brain is not top form (but then again when is it?) so I may not be remembering this right. Twins, while being in almost all aspects the same right down to their finger prints, their DNA does not match exactly. While developing from the same egg that has divided into two separate fertilised eggs with identical genetic material they still develope separatly from each other. This results in slightly different DNA patterns.

If I didn't get that right, somebody please tell me (as I'm sure you will anyway) I may have misunderstood. Biology was NEVER my strong point.

Re:Twins?

[RedBastard]

What would actually happen with identical twins? Twins have an identical set of DNA right? How would anyone know which twin committed the crime?
Well that's obvious isn't it? The normal weight of EVIDENCE would apply - you don't just rely on DNA evidence to solve a crime.

Re:Twins?

[nomadic]

There can be slight variation due to environmental factors in early development, but you're right, it wouldn't be nearly enough to differentiate. So I guess you wouldn't know. Would be kind of maddening though to know that one of two people committed a crime, but not being able to make the charges stick...

Re:Twins?

[Bryan Andersen]

The environmental factors are acting all through out the identical twins life time to make their DNA different. They're know as viruses. Other mutagens will also cause even more differences over time.

Then there is the testing method. The electrophersis gell tests used have rather poor repeatability. Sure some things can be done to help make them better. I wouldn't accept a match when the samples are done on two different machines in different labs. Having two different gel suppliers also makes a huge difference. The test is really only telling you the length of strands between markers where the chemicals split the strands into segments.

Re:Twins?

[TummyX]

Well, if they were conjoined twins then the left one is always the evil one. ...according to the simpsons anyway

take this in perspective

[Anonymous Coward]

When you consider the number of people who have been
wrongly convicted using more traditional evidence and
procedures, I don't think you're going to come up with
a 1 in 37 million failure rate.

Re:Evidence

[Anonymous Coward]

I
Am
Not
A
Lawyer

An Ode to VA Linux

[Anonymous Coward]

An Ode to VA Linux

Hello my dear friends
I am sorry to say,
That I must report sad news
Regarding our hostile takover by VA.

For few people know of the dangerous plan
When the News and the Newspaper are owned by the same man.
What happened to integrity when Mindcraft was paid out by Microsoft?
What will happen to Slashdot when our editors are all bought?

How lucky we are to be a part of this scam
Special offers from VA: Would you care for some spam?
Anonymous Coward reports VA is number one!
This friendly troll asks: Has the end finally come?

Would you like a new server?
How about a new rack?
Would you like some freedom?
Im sorry, we no longer have that.

New server from VA made just for you and me,
A good review of VA, slashdoted, I see.
But did anyone notice what has now become
The death of our trust, our pride, and our freedom?

In conclusion what should we do?
About what here is told?
Lets fight for the truth...
With our rampant incessant trolls!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Its worse than that Jim

[Anonymous Coward]

I remember reading an in depth article on forensic DNA testing a while back and the really frightening thing was that there are actually two sources of DNA which can be used for testing. The really bad thing was that one of them (mitochondrial DNA) is not sufficiently unique to provide conclusive evidence.

The statistics they were quoting were down to 1:600 of having a match with a person drawn randomly. Which is VERY frightening. A jury when presented with DNA evidence tends to just believe that it is conclusive.

l33t

[Anonymous Coward]

elitism is too easily corrupted. I'd rather be tried by my peers than by elite assholes. too bad the current judicial system is so fucked up that my "peers" never are actually my peers. juries are a good idea, as long as they are implemented correctly. in America they are not implemented correctly.

Does this make O.J. innocent?

[Anonymous Coward]

You see... What are you talking about?

Re:Does this make O.J. innocent?

[Anonymous Coward]

I guess the fact that the O.J. defense team proved that the blood evidence had been planted does not mean anything to you. If the police are going to plant evidence, what hope do you have (1 in 13 million).

so the fuck what. increase the loci to 20 dumbfuck

[Anonymous Coward]

get a fucking brain moron mob-mentatliy fuckwads

thats why you test more than 6 loci

[Anonymous Coward]

dumbass

increase the number of loci tested

[Anonymous Coward]

why dont you look at it that way instead?

This wouldn't have happened if they had used...

[Anonymous Coward]

... a Beowulf cluster!

Re:Birthday Paradox?

[Anonymous Coward]

It is when the computer performing the analysis is running a crappy UNIX variant with 1970's-era OS technology.

An Ode to Troll Day (Part 1)

[Anonymous Coward]

An Ode to Troll Day (Part 1)

Gather round all you friends
For I have something to say,
About a new invention
We call it: Troll Day.

A day of great joy
A great fair to attend,
Where everyone posts trolls
And moderation is dead.

It's not like most holidays
Of which you may have been told,
Since we hold it every Tuesday
And everyone gets stoned.

So now I take the pleasure
to invite you all here,
And remind you of our next Troll Day
Held once a week, not once a year.

(P.S. See you on Tuesday :))

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Re:Welcome to the world of statistics . . .

[Anonymous Coward]

This is an interesting and eye-opening occurence, but it isn't the end of DNS evidence in forensics.

So you're saying that the Secret World Government has been incorporating unique IP addresses into everyones DNA, and can identify everyone via the Internet?

That's something to worry about all right.


Wingnut

An Ode to Troll Day (Part 1)

[Anonymous Coward]

An Ode to Troll Day (Part 1)

Gather round all you friends
For I have something to say,
About a new invention
We call it: Troll Day.

A day of great joy
A great fair to attend,
Where everyone posts trolls
And moderation is dead.

It's not like most holidays
Of which you may have been told,
Since we hold it every Tuesday
And everyone gets stoned.

So now I take the pleasure
to invite you all here,
And remind you of our next Troll Day
Held once a week, not once a year.

(P.S. See you on Tuesday :))

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to Threaded Posts

[Anonymous Coward]

An Ode to Threaded Posts

My friends come around
I have something to share,
Would you do me a service
And lend me an ear?

There has been recent discussion
About a poorly known fact:
Why has Commander Taco changed the default display mode
From Threaded to Flat?

I believe I can help you,
For once did I overhear him say:
My friends have I have plotted,
To annoy all Anonymous Cowards away.

The default display mode did he change,
Now to view threaded posts we must reload each page.
But did he consider the excess system load
For he said: we have the bandwidth to annoy these trolls.

To this we must put a quick stop
Though we are annoyed, open an account we will not!
For every proud AC holds freedom quite dear
And is not intimidated by actions done out of fear.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Watch out for your DNA clone...

[Anonymous Coward]

You have a 1 in 37 million chance of being wrongly convicted. This means that you are only innocent if the other 135 people on earth with your DNA match are.

What a jip...

Re:juries

[Anonymous Coward]

Ya know, I've always been suspicious of those numbers. They seem to take "This thing occurs in 1/N th of the population and this occurs in 1/M th of it, so the combination occurs in only 1/NM th of the population" and the very first thing anyone's taught in a probability class is the bogosity of simply multiplying the two! How much checking around have they done to prove the statistical independance of these "loci"?

An Ode to Threaded Posts

[Anonymous Coward]

An Ode to Threaded Posts

My friends come around
I have something to share,
Would you do me a service
And lend me an ear?

There has been recent discussion
About a poorly known fact:
Why has Commander Taco changed the default display mode
From Threaded to Flat?

I believe I can help you,
For once did I overhear him say:
My friends have I have plotted,
To annoy all Anonymous Cowards away.

The default display mode did he change,
Now to view threaded posts we must reload each page.
But did he consider the excess system load
For he said: we have the bandwidth to annoy these trolls.

To this we must put a quick stop
Though we are annoyed, open an account we will not!
For every proud AC holds freedom quite dear
And is not intimidated by actions done out of fear.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to Threaded Posts

[Anonymous Coward]

An Ode to Threaded Posts

My friends come around
I have something to share,
Would you do me a service
And lend me an ear?

There has been recent discussion
About a poorly known fact:
Why has Commander Taco changed the default display mode
From Threaded to Flat?

I believe I can help you,
For once did I overhear him say:
My friends have I have plotted,
To annoy all Anonymous Cowards away.

The default display mode did he change,
Now to view threaded posts we must reload each page.
But did he consider the excess system load
For he said: we have the bandwidth to annoy these trolls.

To this we must put a quick stop
Though we are annoyed, open an account we will not!
For every proud AC holds freedom quite dear
And is not intimidated by actions done out of fear.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to Threaded Posts

[Anonymous Coward]

An Ode to Threaded Posts

My friends come around
I have something to share,
Would you do me a service
And lend me an ear?

There has been recent discussion
About a poorly known fact:
Why has Commander Taco changed the default display mode
From Threaded to Flat?

I believe I can help you,
For once did I overhear him say:
My friends have I have plotted,
To annoy all Anonymous Cowards away.

The default display mode did he change,
Now to view threaded posts we must reload each page.
But did he consider the excess system load
For he said: we have the bandwidth to annoy these trolls.

To this we must put a quick stop
Though we are annoyed, open an account we will not!
For every proud AC holds freedom quite dear
And is not intimidated by actions done out of fear.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

zee problem ees

[Anonymous Coward]

Eyewitness testimony is notoriously unreliable. In Psych class we hearded a bunch of willing testees into the front of a classroom, then had the drama class do their imitation of an armed robbery at the back.

Thirty people, thirty opinions. Hell, they couldn't even agree on skin color of perp, let alone height, fatness, or sex.

This is why the court system wants something "scientific." How many people went to jail for murder after they were falsely convicted on the basis of the gunpowder test. The judicial dweebs didn't know that not washing your hand after urinating made for a false positive, and it took decades for judges to admit their mistakes. I'll answer my question, thousands.

All you have to do is look at the Illinois death penalty system and realize these tests are easily falsified, forget being done correctly. Crooked cops sent Rolando Cruz to death row for a murder he had nothing to do with.

An Ode to VA Linux

[Anonymous Coward]

An Ode to VA Linux

Hello my dear friends
I am sorry to say,
That I must report sad news
Regarding our hostile takover by VA.

For few people know of the dangerous plan
When the News and the Newspaper are owned by the same man.
What happened to integrity when Mindcraft was paid out by Microsoft?
What will happen to Slashdot when our editors are all bought?

How lucky we are to be a part of this scam
Special offers from VA: Would you care for some spam?
Anonymous Coward reports VA is number one!
This friendly troll asks: Has the end finally come?

Would you like a new server?
How about a new rack?
Would you like some freedom?
Im sorry, we no longer have that.

New server from VA made just for you and me,
A good review of VA, slashdoted, I see.
But did anyone notice what has now become
The death of our trust, our pride, and our freedom?

In conclusion what should we do?
About what here is told?
Lets fight for the truth...
With our rampant incessant trolls!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to VA Linux

[Anonymous Coward]

An Ode to VA Linux

Hello my dear friends
I am sorry to say,
That I must report sad news
Regarding our hostile takeover by VA.

For few people know of the dangerous plan
When the News and the Newspaper are owned by the same man.
What happened to integrity when Mindcraft was paid out by Microsoft?
What will happen to Slashdot when our editors are all bought?

How lucky we are to be a part of this scam
Special offers from VA: Would you care for some spam?
Anonymous Coward reports VA is number one!
This friendly troll asks: Has the end finally come?

Would you like a new server?
How about a new rack?
Would you like some freedom?
Im sorry, we no longer have that.

New server from VA made just for you and me,
A good review of VA, slashdoted, I see.
But did anyone notice what has now become
The death of our trust, our pride, and our freedom?

In conclusion what should we do?
About what here is told?
Lets fight for the truth...
With our rampant incessant trolls!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to VA Linux

[Anonymous Coward]

An Ode to VA Linux

Hello my dear friends
I am sorry to say,
That I must report sad news
Regarding our hostile takeover by VA.

For few people know of the dangerous plan
When the News and the Newspaper are owned by the same man.
What happened to integrity when Mindcraft was paid out by Microsoft?
What will happen to Slashdot when our editors are all bought?

How lucky we are to be a part of this scam
Special offers from VA: Would you care for some spam?
Anonymous Coward reports VA is number one!
This friendly troll asks: Has the end finally come?

Would you like a new server?
How about a new rack?
Would you like some freedom?
Im sorry, we no longer have that.

New server from VA made just for you and me,
A good review of VA, slashdoted, I see.
But did anyone notice what has now become
The death of our trust, our pride, and our freedom?

In conclusion what should we do?
About what here is told?
Lets fight for the truth...
With our rampant incessant trolls!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

An Ode to VA Linux

[Anonymous Coward]

An Ode to VA Linux

Hello my dear friends
I am sorry to say,
That I must report sad news
Regarding our hostile takeover by VA.

For few people know of the dangerous plan
When the News and the Newspaper are owned by the same man.
What happened to integrity when Mindcraft was paid out by Microsoft?
What will happen to Slashdot when our editors are all bought?

How lucky we are to be a part of this scam
Special offers from VA: Would you care for some spam?
Anonymous Coward reports VA is number one!
This friendly troll asks: Has the end finally come?

Would you like a new server?
How about a new rack?
Would you like some freedom?
Im sorry, we no longer have that.

New server from VA made just for you and me,
A good review of VA, slashdoted, I see.
But did anyone notice what has now become
The death of our trust, our pride, and our freedom?

In conclusion what should we do?
About what here is told?
Lets fight for the truth...
With our rampant incessant trolls!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

hoax!

[Anonymous Coward]

its a hoax!

Re:hoax!

[Anonymous Coward]

Here is the pineapple you ordered Sir.

Can I get you some Vaseline to go with that?


Wingnut

Re:juries

[Anonymous Coward]

bogostupidity: 6, 10 , 13 what does it matter? People have won the lottery twice - even bigger odds. What if the statistical independenance of the loci is lower, or illegal substances in the perps dna sample affect testing? After this, andy self respecting authority should not perjer themselves by mentioning 'odds' that they have 'read' , and not experienced

Birthday puzzle

[Anonymous Coward]

In a room full of people - odds 2 people have same birthday? Now how about a jail, or police database?.

An Ode to VA Linux

[Anonymous Coward]

An Ode to VA Linux

Hello my dear friends
I am sorry to say,
That I must report sad news
Regarding our hostile takeover by VA.

For few people know of the dangerous plan
When the News and the Newspaper are owned by the same man.
What happened to integrity when Mindcraft was paid out by Microsoft?
What will happen to Slashdot when our editors are all bought?

How lucky we are to be a part of this scam
Special offers from VA: Would you care for some spam?
Anonymous Coward reports VA is number one!
This friendly troll asks: Has the end finally come?

Would you like a new server?
How about a new rack?
Would you like some freedom?
Im sorry, we no longer have that.

New server from VA made just for you and me,
A good review of VA, slashdoted, I see.
But did anyone notice what has now become
The death of our trust, our pride, and our freedom?

In conclusion what should we do?
About what here is told?
Lets fight for the truth...
With our rampant incessant trolls!

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

NATALIE PORTMAN IS HOTTER THAN YOUR GIRLFRIEND!

[Anonymous Coward]

NATALIE PORTMAN NAKED AND PETRIFIED BABY!

United Coalition of Trolls for the Abolition of Moderation

Experts

[Anonymous Coward]

>American experts have called it 'mind blowing'.

It is a good thing we have those expert comments.

Re:Experts

[SlamboS]

I strongly agree!

Re:furst

[Anonymous Coward]

You have posted a "first post". You are now subject to the "AC flame of death". Beware!

[FLAME ON]
HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE!
[FLAME OFF]

Re:juries

[Anonymous Coward]

No, the UK is not just white anglo saxons thank you very much.

Re:thank goodness for the recount..

[Anonymous Coward]

You have posted a "first post". You are now subject to the "AC flame of death". Beware!

[FLAME ON]
HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE! HarveyNeon is such a fucking PUSSY! He molests little girls, the fucking PERVERT! He doesn't deserve the air he's fucking BREATHING! HarveyNeon DIE DIE DIE! What a fucking MORON! He's such a complete ASSHOLE! His parents must have been fucking CRAZY to produce such a total LOSER! He should just put himself out of his misery and DIE! HarveyNeon DIE DIE DIE!
[FLAME OFF]

Re:thank goodness for the recount..

[Anonymous Coward]

He'll probably get an official appology and maybe some compensation. I wouldnt expect hed get too much though. This is not the US and we try not to give people too many excsuses for suing for millions of pounds because they were stupid enough to spill hot coffee in their laps. Having his DNA closely match the suspects is hardly anyones fault. It was just unfortunate.

Re: Terry Pratchett

[Anonymous Coward]

Terry Pratchett is from Britain. He is not Australian.

Re:Make POET TROLL go away

[Anonymous Coward]

Here's your rats ass Sir.

Can I get you a runner-bean to go with that?


Wingnut

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Thoughts on Multiple Postings (A short Poem)

[Anonymous Coward]

Thoughts on Multiple Postings (A short Poem)

My friends an issue I must now address
One which has grown rampant and now runs unchecked,
What do I speak of with half sullen eyes?
I speak of Trolls posting multiple replies.

One time long ago only one post was did one need
Then came moderation: the Demon Spawn Seed.
Now if one wants to ensure that his post chance be seen
Required you hit the submit button until your thumbs bleed.

Now please dont think that I am being rash,
Have you had your post moderated into the trash?
Do you sit and wonder chance you post will be seen?
If did then you'd hit the submit button for 2-53.

Now what can you do to help stop this crime,
Where Anonymous Cowards are treated like slime?
The answer is close and soon shall be yours
If you join me and hit the submit button until your arm's sore.

--
POET TROLL
YOU can make a difference. Join today.
United Coalition of Trolls for the Abolition of Moderation

Re:Statistics and probability

[Anonymous Coward]

Ruben Lopez naked and petrified!!!

Re:Statistics and probability

[Anonymous Coward]

Ruben Lopez naked and petrified!!! '

Re:Statistics and probability

[Anonymous Coward]

Ruben Lopez naked and petrified!!!;

Re:I knew DNA was all mythology

[Anonymous Coward]

Ruben Lopez naked and petrified!!!.

Look out

[Anonymous Coward]

Don't let OJ hear about this. :)

Re:He wasn't convicted

[Anonymous Coward]

He was very nearly convicted. They only re-tested because *** HE HAD AN ALIBI ***. If he had not had an alibi the 10 point re-test would NOT have been done and he would have been convicted on the six point test like many others have been.

Re:Welcome to the world of statistics . . .

[Anonymous Coward]

- as long as it isn't abused. And generally speaking, the various police forces that use it are honest enough that they don't abuse it (witness the fact that they got a second opinion in this case).

THEY ONLY GOT A SECOND OPINION BECAUSE HE HAD AN ALIBI. If he had not had an alibi he would have been convicted on the first test. Simply protesting his innocence would not have got the police to carry out the improved test.

Almost as if they just wanted to convict someone - can then claim to have solved crime thus gaining a promotion or bonus.

The Odds

[Sanat]

Scotland Yards could round up any 56 individuals off of the streets who have not had a DNA sample taken and the odds are that one of those individuals would match one of the 660,000 DNA samples on file.

If a person FIRST was a suspect and then his DNA was tested and found to match the crime scene evidence... then that would be 1 in 37 million odds.

But to compare an individual's DNA with the databank would as others here have said be 1 out of 56 chances. NOT good odds.

It reminds me of the old parlor trick of matching birthdays. I forget the exact number (and to lazy to calculate it) however if 15 (approx) persons are in a group and each of their birthdays are matched then it is favorable that two within the group will have a birthday on the same day.

The same corollary exists for the DNA, except that the police are matching against a database of data.

You would think that the police would be smarter than that. Well, on second though, no....

6 loci, 10 loci, loci-schmoci

[Wansu]

What we're talking about here is pattern matching on something that looks like blobs of crap anyway. 1 in 37 million chance pretty much means it can't happen, assuming that figure is accurate ;^) . But it did. 10 loci gives another, larger but equally astronomical figure. But I've got a hunch this will happen again because this has the look and feel of a fundamental problem. I'm not saying that in theory DNA testing won't work; I'm saying the way we're doing it is fundamentally flawed. The price of a mistake is too high. I'm even more adamant about drug testing. The tolerable accuracy and effacy of a test depends on the eventual use of the results. This is what happens when greedy, unscrupulous companies slap together some half-assed but profitable methodology and put it forth as "science". True science gets a black eye.

Re:Statistics and probability

[John Allsup]

By that count, if you have 37 million samples, the propability equals 1 eventually, and with 74 million, it approaches 2!! The moral of this being that you can't just multiply.

The rule you are mistakenly using is

P(A or B) = P(A) + P(B)

this only happens if A and B are mutually exclusive, which brings with it that 37m samples will guarantee a match. In general, the formula is

P(A or B) = P(A) + P(B) - P(A and B)

BTW, the 1/56 figure is the probability that you have the right person given only the match in the DNA.
John

Book: "Randomness" by Deborah J. Bennett

[MoNickels]

For a good, fast, easy-to-read book on probability, chance and randomness, I recommend "Randomness" by Deborah J. Bennett. I'm reading it now.

At Amazon

old news

[bobalu]

There must be a helluva queue for posting stories here at SlashDot - this story was out on CNN or the NY Times or something days ago.

Only a tiny part of our DNA is human-unique

[Morgaine]

I seem to recall that 90% or more of human DNA is identical to that of everything that came before us, say, dinosaurs.

So, presumably any moment now someone will get prosecuted for some of Godzy's mayhem.

Re:juries

[rve]

What a rediculous, and particularily nasty bit of flamebait...
...or is this a clever troll intended to demonstrate how OJ got off? "The policemen who arrested him were racists, so if you find him guilty, that makes you a racist too. It doesnt matter if he's guilty or not, we have to punish the racist police by finding OJ not guilty". All these arguments weighed heavily enough in the mind of the jury to find the small, but non-zero chance that the overwhealming forensic evidence was the result of an elaborate conspiracy to rob the black community of one of it's icons, ground for reasonable doubt.

Re:juries

[rve]

Really? If the lawyer is convincing enough, the jury will find a 1 in 37 million chance 'reasonable doubt', especially after this incident. Forensic evidence doesn't mean a whole lot to a jury that cosists of people who only get to be involved in a trial once in their life (if they're lucky). Remember how easily the overwhealming forensic evidence was brushed aside in the O.J. Simpson case?

Its not 1 in 37e6 its 1 in 56 duh..

[mal]

Its difficult to believe that bonafide scientist
could be so stupid. If they have 660,000 records
on file, and the chance of a random match is
1 in 37e6, then the chance of matchng someone at
random in the entire database is
1 in 37e6/660,000 = 1 in 56. The bigger the database gets the worse the problem.
If they have been using such "evidence" to put
people away, they must have hundreds of innocents
in the slammer by now.

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[mal]

Hmm I think your reasoning is a little sloppy.
Firstly you assume that each on the loci is
statistically independent, I'd guess not.
Secondly you assume that all gel locations
are equally probable, this has to be wrong, I'd
guess the distribution is highly skewed towards a
small subset of locations.
The article itself states that adding four
additional loci takes you from 1 in 37e6 to 1 in
1e9 an inprovement of a factor of 27 or 2.3 per
loci, a long way from 600!
There must be a strong case of diminishing returns
here, so even the 13 loci tests used in the US are
probably not much better than 10 loci test
mentioned in the article.

Re:juries

[Maserati]

The way I see that trial is as follows:
The LAPD got caught framing a guilty man. Since the police in this country have to play by the rules, there was no reasonable way he could have been convicted. The un-reasonable way would have been to ignore police tampering with evidence and violating the chain of custody, but that would have been worse than letting a guilty man walk free.

I did run that LA Times search URL posted elsewhere, and it's pretty clear that the LAPD will do whyatever they think they can get away with. For example,

If Not Guilty verdicts and overturned convictions are the price we pay to send a message that police misconduct Will Not Be Tolerated, then we grit our teeth and bear it. Remember, America is supposed to be a free society, and police misconduct cannot be tolerated.

Gotta use the technology correctly

[PD]

All your points are true, and that means that people who use DNA testing need to be concentrating on *clearing* people rather than implicating them. A positive DNA match should not be considered to be the final word in guilt or innocence.

Re:Not as unlikely as you might think...

[Now15]

Hehe stupid Aussie comedians hehe

--

Re:I'll take the ignorant over the "annointed"...

[sholden]

>>I'm amazed human rights organisations have not
>>stood up for the right of the defendant to be
>>tried by proper licensed professionals.

>So why not do away with juries altogether? The
>lawyers and judges are all certified, surely that
>makes them elite enough to decide the fate of
>the accused.

Heck, why not just let the police do it. Just add
a certification test to their training...

That would save some of the money spent on the
justice department. Just let the police drop their
supects off at the local maximum security prison.
No judges, no lawyers. Just good old fashioned
martial law.

Problems with this sort of estimates

[orpheus]

First off... IANAMB (I am not a molecular Biologist) -- well, I suppose that technically I am... at least judging by degrees and coursework. However, I never took a job in that field, and I haven't run a gel since the early 90's so a lot f what I think I know may be outdated (this field moves even faster than computing -- largely because we knew so little to begin with)

I love PCR and the million ways it can be used, and I am very happy that it's being increasingly used in criminal investigations. The former 'gold' standard (eye witnesses) have been demonstrated in study after study to be frequently unreliable.

However, when I see a number like 1:3.7x10^7, I really fume. It's based on far too many assumptions that we simply do not have the knowledge to verify. The specifics vary with the loci and methods used, but I think I can illustrate a few major points with general principles.

1) DNA matching is *NOT* done by sequencing the entire sample of DNA available. Instead, a few quick measurements are performed. The principle is that no one individual is likely to match all of them ["Gee, how many green convertibles with a Z on the license plate could have been driving in this part of town at three a.m. last night? One, buster -- you!"] DNA evidence assumes a reasonable degree of randomness and statistical independence, but those qualities are poorly charaterized in the real world.

2) DNA is far from random. In fact (despite the inevitable mutations we all have) it's just a mix-n-match of the DNA of existing humans (who are similarly non-random, breed non-randomly, etc.).

3) Even after we sequence the Human genome, we won't have the information about genomic variance to make such estimates accurate -- until we characterize hundreds of thousands of people in a deliberately random fashion to even come close.
[It *must* be random -- not based on criminals or even volunteers. Many 'classic' post WWII medical studies were heavily biased towards the "70-kg white male medical student" (who will volunteer for almost any test).]

Think about it: how can any statistical analysis claim an accurate probability of 1 in 37 million, from a database of 660,000 individuals? or even 6.6 million? The number was created by assuming the individual measurements were independent -- even 'partial independence' would require a quantification of the degree of dependence for any real calculation. That data does not exist -- and would require millions of test subjects.

3) Variance information would be tricky to interpret, even if we had the data.
"A rare mediterannean genetic trait" isn't quite as significant if the crime took place in Italy -- or 'Little Italy' of your favorite town.
If a witness sends the police on a round up of "short blond female caucasians with freckles", then the probative value of the DNA analysis depends on the likelihood of a match for a random
"short blond female caucasians with freckles", not "tall, dark hispanics" or "short-haired male tabbys with spots"

[Want to start a fight? Ask ten forensic geneticists how the overall odds change if the suspect turns out to have a known identical twin. Even this seemingly simple question has never been completely resolved mathematically. Many investigators will mumble 'No change', but in fact, there clearly is a difference. we just can't quantify it. The same applies, crudely, to an only child vs a child in a large family]

Sadly, characteristics cluster in precisely the way we wish they wouldn't. Relatives share genetic similarities, have a tendency to be in the same general area, and often enough situational factors to predispose to similar motives. The same applies (much less strongly) for ethnicity.

It's important to note that deviations from perfectly independent assortment will ALWAYS reduce the 'odds' of an incorrect match, making any DNA match less conclusive

4) Generally, these corrections tend to have larger effects when the base (uncorrected) likelihood is small (i.e. it's easy for a correction to reduce one in 37 million to one in 10 million, but very hard to reduce 1:4 to 1:1.1)

The article says that the error reflects the rapid increase in the database size (470K to 660K in the past year). However, I think that it is more likely that the error reflects the flaws in the assumptions behind the estimates. As the database size groews (and DNA is nore widely used), we will see more errors -- not because of "all that nasty data" but because "all that data" will highlight (as data is supposed to do) the error of our assumptions.

Re:Problems with this sort of estimates

[Technik~]

I'm no molecular biologist (or lawyer or mathematician, for that matter) but neither is the typical juror who's sole qualification (in the U.S., anyway) is being in the pool of those who have registered to vote and do not have some obvious prejudice against the matter at hand.

The assumptions you detail above and the intricacy of statistics is probably beyond analysis by the typical juror. This means that the jury is weighing not the technical or factual merit of the "experts" but some unknown subjective reason: the persuasiveness of the lawyers, how scary the defendant looks, how many days the case has gone on, or something else. In short, it is only a matter of time before the collection of assumption, error (possibly in procedure or in recording), and juror ignorance produced the result in this British case.

I hope that this acts as a wake-up call here in the U.S. but somehow I doubt it.

Re:Statistics and probability

[orpheus]

The "1 in 37,000,000" figure is presented as a final probablility of a match. Where did you see *anything* about there only being 37,000,000 possible permutations (1 person in 37 million)?

If there were only 37M permutations of 6 loci, that would imply roughly 20 discrete possible values at each loci. Is that how you envisioned the underlying data?

I don't know what test they use in the UK, but I'm assuming that it's the RFLP [Restriction Fragment Length Polymorphism]-- basically they use a highly specific enzyme to chop up the DNA, and place it on a polyacrylamide gel under an electric field to measure the size of the fragments. (Actually, nowadays, they probably use pre-synthesized n-nucleoside primers and PCR [polymerase chain reaction] to chop and selectively amplify the fragments, but the principle is the same)

A single gel can easily measure fragments ranging from a few hundred base pairs to 10-400+ kbp with good resolution. The exact range varies according to current/field, gel composition, and other factors, but the bottom line is: it's easy to see bands that are a millimeter apart, so if you use a foot long gel, the range of possible values is close to 300. that creates:

300^6= 7.29 x 10^14 possible permutations

Actually, 0.5mm is a more realistic resolution limit, so the actual number of resolvable values is at least 600.

(600 values) ^ (6 loci) =4.6x10^16 permutations

These are just crude estimates, for the benefit of those who've never read a electrophoresis gel. In actuality, the range of allowable values might be limited by other factors (values that are too extreme may be eliminated as artifacts) But it does give a sense of the TRUE numbers involved.

(with modern gels and automated readers, the resolution may be even higher, but my experience was with UV lamps, eyeballs and Polaroid prints way back in the 1900's... 1991 or so)

Please run your analysis again using this range of possible permutations, and you'll see that 1:37M could well be a FINAL probability of a false match.

Re:Statistics and probability

[orpheus]

>1: The chance of a DNA match (in this 6-loci
>case) is 1 to 37000000.

Where does it say that? If you'd ever run a gel, you'd know that this is ridiculously low. It implies that there are only about 20 possible 'positions for a band. the actual number of values on a full-size gel is in the 100's

>2: That means that ONE DNA-sample compared to
>ONE other DNA-sample has the chance to in 1 of >37000000.

No, it means (as stated in the article) that the chances of a mismatch OVERALL (under the condition listed for the database) were estimated a 1:37M. I have serious issues with the underlying assumptions of the model used in DNA ID calculations, but they are based on the fact that we lack critical data for the assumption of "independent assortment (a basic concept in first year genetics) but I DON'T doubt the ability oif the statisticians to do basic math. I just think that they made assumptions (required by the limit of current data) that are not justified.

That may be okay for a research paper, but not for a person's life -- no matter how much law enforcement may want answers! [note: the polygraph, inadmissible in most courts and widely discredited as a 'truth tool', is often used in investigations because police want answers, and are willing to accept the "risk" (minimal, to them) of a wrong answer]

>4: Any other circumstances have no impact on this >if THEY HAVE NOTHING TO DO WITH THE DNA-CODE !

Jesu christu, tu mater est stertocarari! I can name a few dozen things unrelated to the genatic code, from start (AUG) to finish (3 codons) that impact the calculation -- lab criteria for artifacts, choice of primer, ethnic dependencies, underlying population composition, inbreeding and genetic relationships with the suspect pool... and if I hadn't been up for days, I'd have a much longer and more varied list

>5: In this case we have 660000 OTHER DNA-samples
>to match against ! The rest is obvious ...

Yes, obvious. So obvious that (as I have shown in another post) the number of independent permutations may well be over 10^17 -- and the 3.7x10^7 figure cited in the article obviously is reduced to take account of this crude pairwise database comparison (and other factors)

Re:Welcome to the world of statistics . . .

[orpheus]

>The most important thing to understand is that
>this anomalous case does not invalidate DNA
>evidence... (assuming the methodology of the
>tests is good) is exactly as useful now as it
>was before

I DON'T hate statistics. I hate what is often done with it.

As a result I can see that the assumption of independent assortment is severly flawed. This makes DNA IDs very useful for its negative predictive value (if it says you're not guilty, you almost certainly are not) but it's positive predictive value is much weaker.

That's why blood tests are far more accurate at disproving paternity than proving it: it may be impossible to prove a negative ["I have never fathered a child"] but it may be easy to disprove a positive assertion ["You fathered this child"]

Orpheus, father of the finest children, bar none

Re:P(false positive) -> 1 as n -> oo

[orpheus]

>This is ignoring the probability of a false
>negative; this is very low since only one person
>can commit a crime!

Your logic is extremely weak here.

Are you saying that if I have lots of co-conspirators, I decrease my chances of getting caught?

Gee-- no wonder white collar crime is so rarely prosecuted

Re:Statistics and probability

[AmirS]

It depends exactly what probability the 1 in 37 million refers to.

I understand it to mean that a given DNA sample, using their testing techniques, will only match 1 in 37 million of the general population.

However, given 660,000 of the general population, the probability of you finding that one has just increased.

The probability you refer to "1 in 37 million that you will get a false match if it is in the database." is what the juries and others are led into believing, but it is not explicitly put that way, because (I believe) that is false.

The article actually says, "British authorities estimated that the likelihood of that match occurring at random was one in 37 million.", which is a totally different thing.

Re:Birthday Paradox?

[Felinoid]

Ooohhh looks like someone dosn't like the prospect of lose marketshare to a free product hmmm?

Ok to get back to the subject....
There isn't that much chance of two people comming up with the same DNA.. Thats the whole point of the DNA fingerprint.

On the other hand it is posable to polute DNA samples... If you have sample a and sample b in the same lab at the same time it is posable to mistakenly mix a and b together...

DNA evedence shouldn't be total proff simply backup evedence...

Juries: The Morons tried by the Ignorant

[Teun]

To drive a car you have to get a licence, but to be resposible for someones life in a trial you only need to be selected........
I'm amazed human rights organisations have not stood up for the right of the defendant to be tried by proper licensed professionals.

DNA Testing Policy

[YoJ]

This fiasco illustrates how DNA testing can be abused. It is NOT ACCEPTABLE to keep a massive file of DNA codes of citizens, then when evidence comes in to match it with the entire database. As others have pointed out, there may be a one-in-37 million chance the DNA matches any given person, but the chance it matches SOMEONE who did not commit the crime can be unacceptably high (1/56 in this case).

The correct use of DNA testing is for verifying suspects. Ideally, evidence is collected at the scene of the crime and a list of suspects is generated. If DNA evidence is found, it is checked against the list of suspects only. Only then is a DNA match meaningful. I think that using the entire database violates the principle of probable cause. Citizens should be innocent until proven guilty. If your DNA happens to match the DNA found at a random crime scene, you should not have to prove your innocence.

Explanation of the math:

Chance of a DNA sample matching another random sample: 1/37e6

Chance of 2 DNA samples matching a random sample: (1/37e6)^2

Chance that neither of the 2 DNA samples match a random sample: (1 - 1/37e6)^2

Chance that none of the 660,000 samples match a random sample: (1 - 1/37e6)^660000

Chance that at least one of the 660,000 samples match any given random sample:
1 - (1 - 1/37e6)^660000 = 1/56.6

-Nathan Whitehead

MATH!

[floopy]

Well there is a 1/37 million chance they picked *this* guy, but that would make it seem that the probability of a random DNA sequence matching *anyone* in this DNA database seem to be rougly 600,000 times that, or just one in 60. (really it would be 1 - (1-1/37million)^600,000 )

Ooops . . . ;-)

[himi]

Too many RFCs . . .

Thanks for the laugh!

himi
--

Re:Statistics and probability

[cainem]

Chances of the technician contaminating the samples || mistake in labelling results || other incompetence || malicious substitution of results || a fit up ? 1 in 1000? 1 in 10,000? 1 in 1,000,000? Still smaller than 1 in 37,000,000.

I'll take the ignorant over the "annointed"...

[Monte]

To drive a car you have to get a licence, but to be resposible for someones life in a trial you only need to be selected........
I'm amazed human rights organisations have not stood up for the right of the defendant to be tried by proper licensed professionals.

So why not do away with juries altogether? The lawyers and judges are all certified, surely that makes them elite enough to decide the fate of the accused.

Death Penalty (a bit offtopic)

[divec]

Doesn't this show that we never can be sure quite how sure we are? However convinced we are that somebody is guilty, they may in fact be innocent. This is an irrefutable argument against the death penalty IMHO.

Re:Death Penalty (a bit offtopic)

[billybob jr]

That and the whole concept of men not being justified in taking the life of other men. But then, that's just my opinion.

Re:Death Penalty (a bit offtopic)

[gorilla]

Illinois suspended executions after they realized that while they had executed 12 people since the reinstation in 1977, 13 people had been freed from Death Row. Those are not good odds.

Re:furst

[noweb4u]

I am going to have to say.. I don't get this facination about first posts, but all you AC's are going to have to go. This is ridiculous and not what slashdot is about or for. Why don't you get out of your bedroom and get a life? You have submitted the "Yet another absolutely stupid Anonymous Coward Post". Beware my wrath, because it is very very undesirable....

And the weakest link is......

[lildogie]

All of this statistical bru-ha-ha assumes that the samples are properly collected and isolated in the first place.

With a test as sensitive as DNA analysis, it doesn't take a lot of contamination to blow the test.

Especially if, as here in the USA, the detectives like to take the samples back to the scene for no good reason (as in the O.J.Simpson case).

As a juror, I would not be comfortable convicting on DNA evidence alone. I could not examine the evidence itself, only what prosecutors tell me about the evidence. In the USA, it is the jurors' specific role to examine the evidence and weigh its relevance to the case. Evidence that cannot be examined by the jurors is thin ice, AFAIC. (Of course, my attitude would get me kicked out in the voir dire.)

Re:juries

[dTinkrer]

DNA testing results do not prove guilt or innocence. The tests *may* be accurate, however, "matching" DNA patterns only show that the DNA specimen is consistent with the DNA of a suspect. Even if current DNA tests were 100% accurate they still could only place a suspect at a crime scene. This, by itself, only suggests the possibility of guilt. I *hope* that nobody has ever been convicted of a crime soley on DNA evidence.

--

Re:Statistics and probability

[Old Wolf]

2: That means that ONE DNA-sample compared to ONE other DNA-sample has the chance to in 1 of 37000000.

3: If You have TWO other DNA-samples to match against you have a chance of match in 2 (TWO!) of 37000000 !
</BLOCKQUOTE>
For a bunch of supposed geeks, you lot are fucking useless at mathematics.
Here we have a classic example of no logic skills at all.
I hardly need to point out that taking "i"'s logic a bit further,
If You have 37000000 other DNA-samples to match against you have a chance of match in 37000000 of 37000000 !
ie. a definite match. However this is blatantly false.

The guy who replied to this message has a bit of sense, although his calculation is irrelevant.

Now, time for another piece of using your brain instead of being a dick. It is blatantly false that the DNA database has a failure rate of about 1/56. I think it is safe to conclude that the 1/37,000,000 chance has <I>already taken into account</I> the fact that there are 660,000 people in the database.

I don't know how the locus check matches (perhaps we need to find a genetics expert here), but it is reasonable to suggest that if there were a 1/37*10^6 chance of a match on six loci, then the chance of a match on one locus is the sixth root of this, ie. about one in eighteen. It seems highly likely to me that each locus check would be more definite than this low chance.

Here's another piece of reasoning: If the chance of two DNA sets matching is 1 in 37,000,000, then the chance is <I>almost certain</I> that two in a pool of 660,000 will match. (Recall the birthday example; if there are 23 people in a room, then it is more than even chances that two will have the same birthday).
The formula here is:
chance = 1 - (37000000! / 36340000! / (37000000^660000))
which I can't really be bothered calculating, but would wager highly (based on my arithmetic intuition) that it's rather close to 1.

Anyhow, my purpose here was to show that one should reach sensible conclusions by using your brain and looking at different angles on a problem; and CHECK THAT YOUR ANSWER IS SENSIBLE before blindly trusting it. Perhaps the court judges could follow that principle. I know that if school students did, then the average marks on exams would be a lot higher.

&lt;/RANT&gt;

Re:Evidence

[Old Wolf]

What the fuck is IMNAL.

Re:Welcome to the world of statistics . . .

[norm_bone]

I wonder something else. The 1 in 37 million odds are based on a random distribution, right? Someone else already commented that since it's possible that people in the same country are distantly related, it increases the chances of a false match. Simililarly, if there are any genetic predispositions towards committing crimes, (or getting caught) it's conceivable that the DNA samples in the database are more similar than they would be if they were randomly distributed.

Re:Statistical problem can be overcome

[jdiggans]

If you have two crimes with DNA evidence that is only this reliable, then more than likely some innocent person in the UK would test guilty.

First, each 'test' is a unique event, no two tests have any impact on each other. That said, for any single given comparison between two sets of human DNA the entire genome is certainly not compared directly for two reasons:

A) That is technically approaching 'rediculous' since the entire genome run out on an agarose gel looks like a big streak instead of the banding pattern we've all seen on Court TV.

B) It's an excercise in futility since a good percentage of all human DNA is repetitious. Some of these repetitious areas define what we look like (since we all basically look the same) and some are just 'junk' DNA that doesn't do anything. Comparing either of these sub groups is fairly futile.

To this end, DNA science instead turns to hypervariable regions of the human genome known as 'marker' regions. It's these marker regions that are actually compared in court cases. And the variability of these marker regions is what leads to the 1:37 million statistical figure.

Now since each trial is independant in a test like this EACH test for DNA similarity has a 1:37 million chance of matching to the level of exactness set by law. It doesn't really matter how many of these trials are carried out, whether its 80 a year or 80 million, each one has the same (tiny) chance of mis-conviction. This would be why the experts are suffering from blown minds about now considering my chances of winning the lottery every weekend are 1:~14million and I consider _that_ rediculous.

As a side note, as our ability to sequence genomic data increases in speed our ability to compare larger and larger regions of human DNA will improve. At the moment it's fairly archaic, we chop each DNA sample with enzymes that cut at particular loci and then see if the pieces come out the same size. It's a dirty method to be sure. Perhaps someday soon we'll be able to just sequence each persons genome and compare them directly ... though I don't see that being a possibility for at least ten years hence as it would require amazing computing power to compare 3x10^9 bases directly as well as some serious sequencing technology we just don't have yet. A typical state-of-the-art capillary DNA sequencer costs $250,000.00 (US) and can sequence approx. 100,000 bases a week. Do the math and you'd need a lot of machines to get 3x10^9 in any sort of court-friendly time frame ... for now!

------------------------------------------------ ---------------
James C. Diggans
jdiggans@excelsior-web.com

Excellent commentary!

[smallstar]

Anyone prefaces their comment with "IANAMB" and then proceeds to make a highly intelligent argument based an actual knowledge deserves to be moderated WAY up.

(Don't even get me started on the people who post random made-up facts like "We have 90% of our DNA in common with dinosaurs" and expect that to be relevant to the discussion)

Thanks for posting something I actually enjoyed reading!

smallstar

Re:Statistics and probability

[kanthoney]

Um, if a match was guaranteed to be in there, then the probability would be one.

Re: Terry Pratchett

[muwahaha]

I think he's actually British. I went to a talk by him once in
Canberra, Australia, and he didn't sound Australian to me.

Alex.

juries

[geeklawyer]

This demonstrated fallibility wont make any difference to a jury. if you wave "science" at them and say "1 in 37,000,000" they will convict. Still at least OUR forensic people are honest and dont alter the evidence to get a conviction, unless the FBI.

Re:juries

[geeklawyer]

yes really. Like most lawyers I've been accused of thinking Im God (except that I exist), but even Im not omnipotent I cant overturn the prejudices of juries. OJ Simpson of course was a good example he was acquitted because he was black and was accused by racist officers. The DNA evidence provided no more than the hook the jury needed to justify their decision to themselves, IMNSHO. There is rarely absolute evidence, and you are right to say that persuasive arguments can sway many a jury but it needs a solid evidential basis mere rhetoric, however impassioned, will rarely sway a jury, *unless* they want to be so persuaded. Nontheless, Originally DNA was said to be right on a 1 in *BILLIONS* basis, and now, even though it has had to be downgraded, I wouldnt fancy my chances arguing it couldnt possibly be my client - unless he was a twin or OJ. Mind you, I dont do criminal trials, no money but I think thats the view many my colleagues would take.

Re:juries

[AndyL]

Right, but If there are 6 billion people on this planet, even given that one of them has commited a crime, what are the odds that you will be accused of a crime they commited? 37Million to one. That's assuming that they even commited one. And that they don't also catch and test him.

Re:juries

[billybob jr]

In the article they specifically state that the probability of a wrong match are as follows:

6 loci: 1 in 37 million
10 loci: 1 in one billion

The FBI tests 13 loci. There is the potential for one in billions chance. It just depends on the testing methodology.

Re:juries

[alleria]

1 in 37 million. There exist roughly, what, 6 billion people on this planet? So for every me, there's about 162 people whose _DNA_ might be mistaken for mine? (assuming this is a linear relationship and their statistics are the same as what I'm calculating.) An rather _unconfortable_ thought, no?

Re:juries

[NastySavage]

Maybe the misere is because the british authorities haven't taken the database size into account when the presented the evidence. It is the view of quite a few forensic scientists that the size of the database does not matter when presenting DNA evidence probabilistically. If this is the case, then taking a database size of 660,000 into account will lower the 37,000,000:1 to 56:1. And then one understands the better that things like this happens. The interested reader can check my arguments out for this in the journal Biometrics ( http://stat.tamu.edu/Biometrics/ ), issue 55 no.3 pages 671-677 (1999). Unfortunately, the paper isn't available on the net, so you'll have pay your library a visit.

Re:juries

[blane.bramble]

Did you read the article - they re-tested with 10 points of reference, which supposedly has a 1 in 1,000,000,000 chance of a mismatch, so it was more a case of not using the most reliable test they could. Also, apparently in the US they use 13 points of reference, which presumably has a stupidly large number for it's mismatch chance. I guess it'll just change the procedure so they use the 1 in 37,000,000 and re-test with a higher level if it matches to confirm it.

Are there any figures for finger print testing? How truly unique is a single finger print, and whats the chance of mismatch with 2 finger prints? DNA testing is still pretty accurate!

There was no mismatch, that is a lie.

[Esperandi]

He matched 5 pairs. There's a chance of 1 in a hundred thousand or so, but it DOES happen (people win the lottery, eh?). After they matched that, they went and ran the check that takes a lot longer on 10 pairs. He didn't match that, so they let him go.

This is like saying that we acidentally killed the wrong guy after releasing an innocent man from questioning. It didn't happen. It didn't even come close to happening, people are just ignoring the guy is sitting at home in his house and that it was the exact same DNA matching lab (the ones that CORRECTLY matched the first 5 pairs) that matched the 10 and said it wasn't the right guy.

Esperandi

Re: British DNA Database Mismatch

[Xenny]

I realise that this could have been a dreadful miscarriage if justice, but let's get things in perspective here: The British Criminal Justice System is, in many ways, held to be one of the fairest in the world. In most respects this is probably correct due to the copious layers of burocracy making most (I said *most*, not all!) forms of corruption difficult to get away with. However there are some great, gaping holes through which either criminals get off their charges or innocent people are found guilty. I guess it's even worse in the US, where the 'celebrity lawyer' enjoys a much higher cult status than over here. A fashionable lawyer can work miracles, whether you're as guilty as sin or innocent as the day you're born. I guess what I'm rambling at is that there might be a few more false positives (gasp, shock, horror) found after this case, but it's a drop in the ocean compared to the number of people who are wrongly convicted or cleared *every day* due to the power of persuasion which some legal people have. Let's keep it all in perspective, folks.

Mind blown American expert.

[threaded]

I was taught:
X is the unknown quantity,
a spurt is a drip under pressure.

So a 1 in 56 chance actually happening blows the minds of some 'American experts'. Scary is the word that comes to mind. So it's easy to mock journalists. Mock mock mock.

Re:Mind blown American expert.

[T.]

I couldn't help but notice the obvious reference to an RFC. I enjoy that somehow.

this should be considered in context

[hruntrung]

The guy was a suspect, and was released after a more accurate test showed him not to match the DNA from the
criminal. These kinds of problems actually happen with
fingerprints too, as for purposes of searching the databases
they only use something like 29 features of the fingerprints
for matching by computer, then use humans to make exact matches.

That said, even if he had been convicted, this one case
in 37 millions doesn't even begin to compare in magnitude
to the number of people who have been wrongly convicted
by eyewitnesses and the like.

bitter, but true.

[geeKing]

I have been reading these posts for a while, and it makes you wonder if there are more innocents out there, and if those numbers are right...

odds not so great

[geoff lane]

The actual odds of a false positive are much, much lower than 37M:1. The DNA comparison is much like a fingerprint comparison. Only a limited number of points are compared, if they match then it's counted as a DNA match. What a match is is often down to human opinion and thus is quite falable.

660,000 "possible suspects".

[Murmer]

That's the most frightening part of the article, to my mind. Not 660,000 people, or samples to compare, but "possible suspects". The implication, of course, is that every person who's ever given a DNA sample to the police is a suspect in every crime the police investigate through DNA evidence.

Great. Guilty by association, and there's two-thirds of a million associated people. I wonder if the cops take a sample, and you prove not to be guilty, if you can insist that your DNA be removed from the database. I doubt it, though.

--

You're all doing statistics incorrectly

[SIGFPE]

We have no idea what the odds are because all of the calculations you guys are posting assume independence. The probability distributions for different peoples DNA are *not* independent because DNA is inherited along family lines. Shared inheritance means a much greater chance of shared DNA. Forensic scientists probably have no clue how to work with non-independent probabilities - they probably haven't even considered the possibility.

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[jareds]

If the 1 in 37M figure was the final probability, they must have taken the size of the data set into account. But if that was taken into account, why did the article say:

• "British authorities say the mismatch probably was caused by the rapidly increasing size of their database, which has grown from 470,000 potential suspects to 660,000 in the past year."

Also, your numbers are too high to come out with a final probability of 1 in 37M.

Re:thank goodness for the recount..

[cehf2]

IMNAL, although the likelyhood is he can not sue, and rightly so. You can sue for wrongful arrest, but from the article it seems as though he was only called in for questioning, plus the Police had a good reason to bring him in, so that probably also means he can not sue.

All you Americans must realise that you sue far too much, and unfortunately the rest of the world is going that way as well :(

Re:Evidence

[cehf2]

Where does it say he was prosectued? from the article it looks as tohugh he was just brought in for questioning, provided an alibi and they re-checked the DNA evidence. There is a big difference between being Questioned and being Prosectued.

Re:Statistics and probability

[cehf2]

I don't know how you get to 1 in 56, but from my Maths, and the knowledge that the match *might* not be in the database, the chance is 1 in 37 million that you will get a false match if it is in the database.
The point is that the DNA might not have been in the database. If it was guarnteed to be in there then you would be right, perhaps.

Re:Evidence

[cehf2]

Even so I don't think you can even sue if you are found innocent, although as I previously said IMNAL. If you could sue, the government would have a lot less money, or maybe you can and that is where our taxes go :)

Re:Statistics and probability

[cehf2]

ok, I was wrong :) indeed there is a possibility of 1 in 58 of a random DNA segment having a match in the database.

Although if you are in the database you have previously commited a crime, so there is a good reason for suspicion if you do match.

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[ClarkEvans]

Yes, and they were saying that this could lead to a bunch of re-trials in the United States. From my knowledge most of the DNA related stuff in the US is used to relate DNA from a scratch, hair, or other item left at the crime scene to a particular individual. In this case, the probability is far less... although, this could be used to *find* potential criminal that might be scary. Might lead to a national DNA database for finding potential murders... I guess you would be guilty untill proven innocent in this case. Thoughts?

It's a bad day for some one...

[Tokyo Joe]

Here in New Zealand we had some DNA problems last year. In one case a man was wrongly convicted of a crime (rape of a little girl) despite being in a different city when it happned.

Essentially the jury belived that the DNA test was 100% accurate and that there fore the man, and all the witnesses (all of them) were lying.

I can understand that, when you have a dodgy looking normal Joe charged by the Police force, repectable scientest types stating how accurate the tests are etc etc then poor old Joe is scrwed.

The sad thing was the people doing the DNA tests F%&#D up. Further tests (after a couple of years in jail) proved that this man wasn't the Rapist!

Re:It's a bad day for some one...

[Michael Woodhams]

We in New Zealand have beaten the British once again. A similar DNA analysis linked a man to two seperate crimes - the slight problem being that as he was in prison in a different city, he had a (literally) cast iron alibi. This differs from the British case in that it was presumably a lab contamination problem rather than chance match.

I think the previous poster is confusing this with the Doherty case. About 6(?) years ago, an 11 year old girl was raped in her room at night. She positively identified Doherty, a neighbour, as the rapist. About 2(?) years ago he was released when advances in DNA testing were able to show that he was not responsible.

In another recent controversial, high profile murder case, evidence included some hairs found on the accused's yacht, with a DNA match to one of the victims. The defense pointed out various possibilities for contamination in the lab. The accused was found guilty, but only the jury know how much weight was put on the DNA evidence.

Re:thank goodness for the recount..

[HarveyNeon]

Q: you know what the funniest thing about that is?

A: ...me neither.

hehehe. i think i'm soooo funny.

but really, i did a 'furst' post, not a first post. and besides, I apologized.
what about an amendment to andy warhol's "15 minutes" saying.. something like 'Every geek will, once in their life, be entitled to a first post and offtopic reply string,' or something along those lines? huh? what about it?

hehehe. i think i'm soooo funny.

furst

[HarveyNeon]

sorry couldn't resist.

Re:furst

[[nf]kernel]

And just how old are we, sir?

thank goodness for the recount..

[HarveyNeon]

this story sounds like the introduction of a new (actually wouldn't be surprized if this is the basis of an actual) john grisham novel.
can you imagine the horror that the accused must have gone through? poor 'bloke' will probably be able to sue pretty nicely, though. what's the basis of law in britain, more like canada than california i hope..?
for the sake of Charles P. Taxpayer Jr. that is.

Re:Are those in the DB likely to have similar DNA?

[Vanders]

presumably because they have committed some crime

Strangely, not so. In Britian at least, the Police may ask you to provide a DNA sample, generally to exclude people from a crime (This is generally used in cases such as a sex attack, killing etc.) You are not obliged to give a sample, but many people do.

There is nothing to stop the DNA sample being added to the National database even if you have not commited a crime. This was the situation in this case, the gentleman in question had no previous convictions, but had provided a DNA sample in the past.

Evidence

[Vanders]

The most amazing thing about this, is that the police now seem to rely on Forensic evidence so much that the prosecuted the man in question.

The most astounding thing about this, is that the suspect in question was disabled, epileptic (IIRC), had never even been to the place where the crime in question was commited, and had a rock solid alliby for the time & date the crime was comitted. Scotland Yard ignored all of this, and prosecuted solely on the basis of the forensic "evidence".

How many more people who are protesting their innocence, have been convicted on the basis of forensic evidence alone? How many of these convictions could now be wrong?

Re:Evidence

[Vanders]

Not just brought in for questioning, but the Crown Prosecution Service did start procedings, which where dully droped. Although it did not go to court, the CPS were prosecuting.

Prosecutors Fallacy

[Thiarna]

I heard about this. I understood at the time that it was illegal to explain the mistake in UK courts, because it would just confuse the jurors. The only article I can find about it now, here says its only discouraged.

What they forgot to mention..

[Sarin]

The real burglar was this guys long lost twin brother who was switched at birth. :)


Regards,

So - what?

[moeffju]

This had to happen one time. Statistics are, well, just statistics. They can't tell you anything about how often or when something will happen in a specified time. Statistics only tell you how mouch it should happen, according to previously gathered data. The problem arising with this is another: It's the problem of relying on forensic analysis, even when the suspect has got a water-proof alibi and eye-witnesses who can prove the opposite. There were already enough cases of innocents who were found to be guilty. This will just add to this, as DNA tests are believed to be 100% exact. Well, you now know they aren't. Act accordingly.

The system is already flawed

[DrSkwid]

DNA is not randomly distributed. It changes a bit between parent and child. Using 6 loci there is a chance that someone else in your home town will match you. As more and more people are added to the database more and more false matches will occur. This system can only be relied upon to "prove" guilt where every loci is tested. Proving "innocence" of course only requires one non-matching loci.
Although a valuable tool to the state it's infallability is overstated to juries with the "millions to one" maths smokescreen.
I expect it is more usually used as something to present to the defendant to make him/her confess and if they don't who cares, the jury will believe it anyway!


.oO0Oo.

Re:The system is already flawed

[sjames]

This system can only be relied upon to "prove" guilt where every loci is tested.

Even if all match, there is a very tiny but non-zero probability that the match is a false positive. The question then is how much doubt constitutes reasonable doubt? (Or the equivilant phrase in non U.S. courts).

Re:Are those in the DB likely to have similar DNA?

[DanMilburn]

Apparently, in Edinburgh, the police have started compulsory DNA sampling for any offence, from being caught speeding upwards.

This is bad news IMHO.

He wasn't convicted

[mangu]

They re-tested with more loci and found him innocent. One negative is enough to absolve.

This is the advantege of forensic evidence, there's always the possibility of re-testing and the numbers you work with may be statistical, but at least they are numbers.

OTOH, what about eye witnesses? What's the probability of an eye witness be mistaken? In particular, what if the eye witness has racial, social, or any other sort of prejudice against the accused? What if the witness has been manipulated by the police? (This always happened in the Perry Mason stories, at least)

Only forensic evidence should be allowed at courts, eye witnesses are too unreliable, we should do away entirely with them.

From the /. moderator guidelines: If you can't be deep, be funny

Statisical meaning and possible interpretation

[e-Motion]

If the chance of a match between two random DNA samples is 1/37.10^6, and they have 660000 samples in their database, then the likelihood -- assuming their system does'nt give false positives, which I doubt -- of a database match is ... 1.78% !!! We don't know how much DNA tests they make each year, but it's porbably well over a thousand, wich leads to over 10 false positives a year!
From the article: British authorities estimated that the likelihood of that match occurring at random was one in 37 million.

I have always found that the real problem with statistics is determining what they mean. There are some ambiguities in the statement presented in the article.
What do the odds presented describe? Does it mean that there is a one-in-37 million chance that if you compare person X's DNA to a random person Y's that they will match? Or does this mean that the odds that person X's DNA will match any person within an extremely large database (one that theoretically could consist of the DNA of all of the people on earth) are one in 37 million? In the latter case, the statistic given seems very powerful. If there was only a one-in-37 million chance that they would match your DNA falsely when compared to all humans on earth, then DNA testing seems very reliable. In the former case, the statistic seems unconvincing.
Also, I feel that it is important to note that DNA tests, to the best of my knowledge, are not performed "at random." While I admit that I am no expert on police procedure, I would assume that, typically, there is some evidence against the person who is on trial, and once they have pinpointed that person, they test to see if the DNA found at the scene of the crime matches that of the person. Here you introduce even more coincidences, like being in the same location as the DNA, knowing the victim, having a motive, etc. In this light, the odds seem to be almost astronomical. What are the odds that the person that the DNA matches lives in the same area, has a motive, was seen near the scene of the crime, etc? The seemingly large pool of 660,000 gets smaller very quickly. Assume that typically the pool you would test is around 20. The odds for a bad match there look more like .000054%. Still fairly large, but not too bad. It shows that DNA evidence is very convincing, but doesn't stand that well on its own. Hopefully, in most cases, if you did a test of all humans, you'd get a random guy living in China connected to a crime in Idaho rather than a local connected to it. Of course, we're just playing the odds at that point =)

This is not mind-blowing; it is good data

[T.]

All good scientific data is couched in probability, no? I would say that this very unlikely event is, even after its occurance, statistically insignificant. In any case, to increase the assay by a locus or two, or to even double the sampled loci, would not really increase its perceived accuracy in the courts. (By all means, this sort of analysis is far more reliable than a trivial fingerprint identification; and I would guess so by orders of magnitude.) By the way, the greatest random error is introduced at the stage of polymerase chain reaction. The inherent error in this step of the analysis vastly overwhelms the rather insignificant probability of computer error.

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[T.]

You should perhaps check your calculation (and then gracefully rescind your proposition.) If the stated proabability is 37 * 10^-6, it cannot be 1.78%! This is absurd regardles of the size of the database. If not convinced, then I submit the following thought experiment: Does the proabability of error approach zero as the number of samples in the database approaches infinity?

Make POET TROLL go away

[T.]

Who gives a rat's ass about Unix? This story was about DNA, ye freak!

Odds

[SlamboS]

Just wondering, did they say that the odds were one in 37 million for any one person to match another person at random? When only looking at 6 loci? Or did they say that the odds are one in 37 million that someone would match someone else in their database? Because with 660,000 people in the database, that would cut a 1 in 37 million chance way down. 37 Million/660000 = about 56.

Reminds me of the movie "Brazil"

[mgpeter]

the whole buttle/tuttle thing revisited, at the europeans asked for an alibi before killing him! what does DNA stand for ? NATIONAL DYSLEXIC ASSOCIATION

Re:Statistics and probability

[blane.bramble]

Your maths is WAY off. If the DNA sample has a 1 in 37 million chance of being repeated, and there are 660,000 items in the database, that does NOT give 660,000 : 37,000,000 any way you slice it. What it DOES give is a 660,000 : 37,000,000 chance that they have the sample on file, so:

1 : 37,000,000 chance the DNA could be duplicated

1 : 56 chance a similar sample will be on file

1 : (56 * 37,000,000) the sample matches AND a previous criminal has that DNA on file

1 : 2,072,000,000 chance - you can understand why they considered it to be final. Population of Britain approx 58 million

worrying; not our DNA, our legal system

[ironduke-particle]

I read about this. The man had a solid alibi; Parkinson's disease or some such, and since he couldn't dress unaided, could barely stand unaided, I doubt I as a juror would have convicted. But, the local police force -- not necessarily the brightest people on the planet -- were determined to prosecute anyway. That the six common loci test matched is a surprise; that the ten loci test did not match is not a surprise. We should all be on our guard for fatheads who don't understand what their scientists tell them, and for people who cannot understand that a tiny bit of cross contamination does matter when performing polymerase chain reactions.

Why OJ got off

[Jett]

http://www.latimes.com/cgi-bin/archsearch-cgi?DB QUERY=keywords%28police+corruption%29&DATE =last+6+months&SECT=&SORT=d%3Ah&NITEMS=25

There is little justice when the police are criminals.

Hmmm...

[Akaji Monkey]

Reminds me of a case in the late 70s or early 80s (I think) where the jury convicted a guy for bank robbery on the basis of fingerprint evidence, even though there were several witnesses that testified to seeing him in a different location at the time the robbery was taking place.
I don't remember precisely, but I believe that the police had faked the fingerprints using prints that were already on file; it came out when someone realized that the prints used copy toner rather than fingerprint powder.

Moral of the story? The solider the evidence, the higher the probability that it's been faked ;)

Re:Statistics and probability

[TomV]

Not quite. If you are in the database you have been *convicted* of a crime

That would be nice, but in the UK is sadly false. As of a couple of months ago, the sample is taken when you are first questioned. For example, if you are stopped for suspected drunk driving (which is a BAD BAD thing, by the way), the Police are entitled to demand a DNA sample even before they breathalyse you. This sample, or rather the profile from it, remains on file thereafter. Even if you are acquitted. Liberty and several other bodies are trying to get this overturned in the courts, and it will probably be revoked once we incorporate the European Convention on Human Rights later this year.

But for the time being, if they want a sample, they can get it. And if they then want to blackmail you over that embarrassing congenital condition, they can go ahead.

Incidentally, in the UK you can certainly sue the authorities over unlawful imprisonment. Consider the cases of the Birmingham 6, the Guildford 4 and the Maguire 7, all convicted of terrorist offenses in the 1970's and all convictions quashed in the early 1990's because it was overwhelmingly clear that they were all fitted up.

TomV

1:370000000

[nomadic]

So why not just make all the tests 10 loci? or 20? Or 100? Even better, just do two separate 6-loci tests, which would knock the chances of a false match up quite a bit (what would it be, 1 in 136,900,000,000,000) I'd think if the case was important enough, the resources would be allocated.

Re:1:370000000

[cshotton]

So why not just make all the tests 10 loci?

This point is the only valid take-away from the whole article. The British database only captures a DNA fingerprint based on 6 loci and we've all seen the math on that. The vast majority of US states and all federal cases require DNA tests with more than 10 loci. The odds of this error cropping up in the states is significantly less.

p.s. This is an *old* story. It was reported at the beginning of the month in several British papers and ran on CNN on Tuesday. Granted, Saturday night is a slow time for Slashdot, but it'd be nice to hear stuff we didn't already know. :)

Re:Twins? check out those URL's

[#barcode]

check out do identical twins have... and why do identical twins... . They both say that the DNA of identical twins is notexactly the same due to slight changes caused by environmental influences (already starting before birth). Probably it hasn't always been easy to tell the difference between two pieces of DNA that similar. I wonder though - the articles seem to suggest that even the DNA of a clone could be slightly different from the DNA of the being the DNA for the cloning was taken from. Does this mean we might eventually find ways to change one's DNA enough to avoid identification with DNA-samples taken say a few years back, for instance through the influence of viruses that cut little DNA bits and insert them somewhere else...

Re:Are those in the DB likely to have similar DNA?

[pecker]

In Denmark, the police want to build a DNA DB of everyone who has been charged, even if there is no conviction. Worrying.

The rest of us can shut up now

[Perdo]

With the possible exception 1:56, the rest of us computer geeks can shut up. Orpheus has shed light on DNA like the rest of us ought to, but do not, shed light on linux. His depth and research have made us all look pretty weak. Not to mention his other two well thought submissions on this topic.

Are those in the DB likely to have similar DNA?

[mrjuicy]

I don't know much about DNA etc...but are those who make it into the DNA database - presumably because they have committed some crime - more likely to have similar DNA than the rest of us?

Of Juries and Forensics...

[Seb Rabit]

Juries, 12 good men and true... They are supposed to decide that it is beyond ALL reasonable doubt that the accusexd is guilty. Forensics attempts to proove de fact that the suspect commited the crime. It is evidence in the trial, not the trial it self. It's accuracy should not be questioned any more than a finger print, in fact, it is probably the most accurate piece of evidence in the whole courtroom come trial. However... it does not imply guilt. Guilt is determined by the Jury. By parading Scientists on teh dock ad reports and accuracy, we are removing the need for a jury... the decision is now in the hands of the labcoats. What needs to be adressed is the issue that, regardless of the accuracy of the tequnique, it does not decide guilt/innosence, it is a piece of evidence like any other, open to interpretation and to challenge. Tell the Jury to do it's job and not be blinded by Science.

This is what happens...

[sjames]

... When prosecutors abuse scientific evidence with pseudoscience. DNA evidence is exclusionary in nature, not inclusionary. In other words (assuming no procedural errors etc) no match = didn't do it, match = COULD have done it. Of course, prosecutors would have the jury believe the opposite. If science is to be used to convict, then scientific thinking MUST be involved if there is to be fairness. No proper scientist would consider a DNA match on 6, 10, or 16 loci as conclusive (but would consider it a VERY strong reason to investigate further).

Consider the 1 in 37 million. If the database were complete for the world population (about 6 billion), that means that on average, any given DNA sample would appear to match 162 people. The 16 locus test that the FBI uses is better, but still is not damning in and of itself.

Now, add in procedural error and other bad thinking and you have (to me) reasonable doubt unless there is some other evidence.

I am certainly not against convicting criminals, but I AM against decieving juries into believing that a DNA match is damning evidence. Matching DNA evidence should be regarded as the beginning of an investigation, not the end.

They reported problems with DNA testing long ago

[Malc]

I seem to remember watching a programme on the TV about this (can't remember which one, it was along the lines of an investigative news magazine programme, probably after 9.30, probably on the beeb, I think), and it was at least 4 - 5 years ago. I know it was in that time frame because emmigrated 3.5 years ago.

Anyway, they made a claim that the current DNA testing at that time was flawed and often made matches that were incorrect, flying in the face of the astronimcal odds. I think that there were two stages to the problem, one was cross-contamination, and two, the cloning process that makes the sample big enough for testing cloned the contaminating DNA too.

Perhaps the labs were using the same containers for both the evidence DNA and the sample DNA without proper cleaning between tests? It only takes one fragment of DNA to screw the whole thing up. I think that there was serious concern about the use of cost-cutting independent labs who were bidding to do this work for the police at the lowest possible rate.

How is this mind-blowing?

[Millennium]

They used their tests improperly, and they call it mind-blowing?

Look. It's a 1:37-million chance if you're comparing one person's DNA to one sample (probably found at the crime scene) That's why you only use DNA testing to weed people who couldn't possibly have been involved from a very narrow range of subjects. You can't pick out one suspect from a huge list.

This is the problem with archiving everyone's DNA. You know it'll be used for stuff like this, because law enforcement will get lazy.

DNA testing is a Good Thing. It's a very safe, reliable way to identify suspects. But only if you use it properly. This is hardly a "proper" use of the tests, and I'm not at all surprised that this happened. It's a case of lazy law enforcement more than faulty testing.

Re:Statistics and probability

[PG13]

This is a very important point and should be moderated up.

It makes the utmost difference whether the police have a suspect and then use DNA matching to see if he did the crime or if they use DNA matching to find a suspect. As this poster mentions it is then a much lower probability that you did in fact commit the crime.

It is exactly the same as disease testing. If you have a large population which is uninfected (not guilty) a positive match even from a very reliable test is highly likely to in fact be an error.

Of course if you up the test to some obscene number of points you can probably make the probality of error very small again. Of course this leaves the scary possibility that people are falsely convicted because they left a hair lying around...but their are always false convictions.

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[Nicolas MONNET]

Maybe I did'nt express myself properly ... I'm talking about a random DNA sample matching a sample in the database (assuming that those are unique). In that case the likeklihood of a false positive reaches 1 when the database has 37 million entries.

More statistical problems

[tilly]

Everyone and their dog has shown that /.ers actually understand basic statistics. With a 1/37 million chance of a match between two people, and 660,000 people in the database, the odds of eventually coming up with a false positive eventually become quite high.

What not so many have pointed out is that the true odds are probably lower than 1/37 million. That figure is based on the contents of each loci being independently distributed. (With about 1/18 of a match at each loci.) Well we know that is strictly not true - after all a sibling of yours will have 1/64 of getting the same loci from the same source that you did. But are there any larger effects?

The answer is that there is. Suppose that some of the loci have a different distributions in frequency between anglo-saxons, Celts, and East Indians. Then the chance of finding a match between 2 East Indians could be far higher than they estimate. For instance if that 1/18 figure was changed to around 1/9, the chance of matching 2 East Indians now becomes about 1/530,000. Even if your database has only 50,000 East Indians in it, if an East Indian committed the crime, the chance of a false positive is around 10%. Much higher than you would expect. (I am using East Indians because I understand that they are a disliked racial minority in England. Substitute your favorite group if you wish.)

So the moral of the story? Not only is the technique going to inevitably produce false positives, but it is likely to do so in a racially biased manner!

Regards,
Ben

Re:Statistics and probability

[i]

I don't know where you get YOUR math from but it's not relevant.

1: The chance of a DNA match (in this 6-loci case) is 1 to 37000000.

2: That means that ONE DNA-sample compared to ONE other DNA-sample has the chance to in 1 of 37000000.

3: If You have TWO other DNA-samples to match against you have a chance of match in 2 (TWO!) of 37000000 !

4: Any other circumstances have no impact on this if THEY HAVE NOTHING TO DO WITH THE DNA-CODE !

5: In this case we have 660000 OTHER DNA-samples to match against ! The rest is obvious ...

Thomas Berg

Mundus Vult Decipi

Birthday Paradox?

[Detritus]

Is this sort of false match inevitable when you are comparing large numbers of DNA fingerprints from unsolved crimes to a large database of DNA samples?

The question I ask...

[FallLine]

Your points are all valid. However, none of this means that DNA testing is not extremely valuable. In fact, no matter how you figure the odds (within reason). the odds of a person who is WRONGLY suspected being cleared quickly by DNA are likely higher than they are of a person being wrong convicted based on DNA. Knowing what we know through years of experience with DNA, we know that the odds of a false positive are still very slim, even if you factor in human error. If the odds of being wrongly conficted of a crime are a mere one in 36m (or whatever figure you might happen to quote), and DNA proves to be usefull in solving a great many crimes, the question you should also ask is can we afford not to use it? Think of how many people have been cleared by DNA. Think of how many murderers have been convincted and/or arrested before they could kill again. Do you honestly believe that the number of people wrongly convincted (based on DNA) exceeds (or even remotely approaches) the number of people who've been saved? How many people have been wrongly convicted based on DNA? The closest thing, to my knowledge, is this ONE (out of how many million?) guy in the article here, and he was not even convicted. I suspect any lawyer worth his weight could have refuted that, especially if the odds (based on the agreed premises) are as high as most slashdoter's have just purported (e.g., 1:56).

Sure, all things being equal, I would prefer there be no chance of anyone being wrongly convicted; however, the fact of the matter is that we don't live in a perfect world. We were no better off before DNA testing. All we've ever been able to gaurantee in the courts is due process. There has always been (and likely always will be, to some degree) human error and prejudice involved in any trial. DNA, despite its flaws, brings us that much further away from those kinds of errors...

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[orpheus]

I'm sorry you felt a need to take such a strong tone in your title

The "1 in 37,000,000" figure is presented as a final probablility of a match. Where did you see *anything* about there only being 37,000,000 possible permutations?

If there were only 37M permutations of 6 loci, that would imply roughly 20 discrete possible values at each loci. Is that how you envisioned the underlying data?

I don't know what test they use in the UK, but I'm assuming that it's the RFLP -- basically they use a highly specific enzyme to chop up the DNA, and place it on a polyacrylamide gel under an electric current/field to measure the size of the fragments. (Actually, nowadays, they probably use pre-synthesized n-nucleoside primers and PCR [polymerase chain reaction] to chop and selectively amplify the fragments, but the principle is the same)

A single gel can easily measure fragments ranging from a few hundred base pairs to 10-400+ kbp with good resolution. The exact range varies according to current/field, gel composition, and other factors, but the bottom line is: it's easy to see bands that are a millimeter apart, so if you use a foot long gel, the range of possible values is close to 300. that creates:

300^6= 7.29 x 10^14 possible permutations

Actually, 0.5mm is a more realistic resolution limit, so the actual number of resolvable values is at least 600.

(600 values) ^ (6 loci) =4.6x10^16 permutations

These are just crude estimates, for the benefit of those who've never read a electrophoresis gel. In actuality, the range of allowable values might be limited by other factors (values that are too extreme may be eliminated as artifacts) But it does give a sense of the TRUE numbers involved.

(with modern gels and automated readers, the resolution may be even higher, but my experience was with UV lamps, eyeballs and Polaroid prints way back in the 1900's... 1991 or so)

Please run your analysis again using this range of possible permutations, and you'll see that 1:37M could well be a FINAL probability.

Actual experience counts for something. (And as someone who still likes to consider himself a Young Turk, I hate myself for saying that!)

Statistics and probability

[AmirS]

1 in 37 million ?

I don't think so. Maybe onle one person in 37 million would match that DNA, but they were searching from 660,000 people. That makes the probability 660,000 : 37,000,000 or more plainly,
1:56.

I bet that figure never came up at trial. This is blatantly a case of a mis-understanding of probability, from what I have read about the case. They have to use DNA to narrow the search from a few suspects, instead of using it to pick out a person from 660,000 previous convicts.

Re:Statistics and probability

[divec]

> if you are in the database you have previously committed a crime

Not quite. If you are in the database you have been *convicted* of a crime. You may not have actually been guilty. For this reason, your previous track record cannot legally be taken into account when deciding whether you are guilty.

Re:Statistics and probability

[divec]

No, the original poster was right. The chance of a false match on the file is

1 - (1 - 1/37million) ^ 660,000

which is nearly the same as

660,000 / 37million = 1/56.

I knew DNA was all mythology

[r2ravens]

He's at it again, that damn trickster Loci. He makes trouble wherever he goes. And now the FBI has 13 of him... boy are they in trouble.

Welcome to the world of statistics . . .

[himi]

IANAS (in fact, I hate that branch of mathematics with a passion), but I do know enough to be able to say that this is inevitable .

They say there was a one in 37 million chance of this false match occuring - so? There's a one in multi-millions chance of someone winning the lottery, and yet it generally happens (I realise they're not equivalent cases, but it does show my point) - whenever you talk about probabilities, you have to realise that they are only relevant over a statistically significant sample size. They say nothing about individual cases - anomalies happen, the one-in-a-million chance does happen, and almost certainly will happen if you take a large enough sample.

The most important thing to understand is that this anomalous case does not invalidate DNA evidence - all it does is highlight the statistical nature of such evidence. DNA evidence (assuming the methodology of the tests is good) is exactly as useful now as it was before - that is, very useful - as long as it isn't abused. And generally speaking, the various police forces that use it are honest enough that they don't abuse it (witness the fact that they got a second opinion in this case).
This is an interesting and eye-opening occurence, but it isn't the end of DNS evidence in forensics.

himi

--

Re:Welcome to the world of statistics . . .

[jflynn]

Truly.

To be specific, if their database has 700000 entries in it, it has 700000*699999/2 pairs in it. That's 245 billion pairs. If the odds against any pair matching at random is 37 million to one, that means there are a *LOT* of matches in that database, probably about 7000 of them.

This simply seems to be a case of scaling the database without scaling the identification key --with predictable results, non-unique keys.

Anyone know how the probability of a bad match decreases with number of loci tested?

Re:DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[dsplat]

This issue was mentioned in some circles (not the mainstream press, unfortunately) in the wake of the OJ Simpson trials. The problem is that the public, and most of the pundits, it appears, were not educated about the fact that the odds of a false negative and the odds of a false positive are related but not the same.

This brings up too issues. The first is the tendency to believe that technology can put complex techniques within the capabilities of people without training in the field. The second, closely related, is the belief that the reliability of the technology is not effected by the possibility of human error. On anything where the odds are stated as being that long, the two things I always ask are:

1. Do we understand the odds? Are we aware of all of the factors that might be significant when we are trying to get results to that many decimal places? There are any number of factors that can be ignored when you are looking for imprecise answers.
2. What were the opportunities for human error or corruption? I would expect them to be fairly high relative to the long odds stated here.

DNA is evidence, not proof

[Myriad]

This really shouldn't come as that big a surprise to people - no more so than someone winning a lottery.
As the article mentions, there is a 1 in 37 million chance of this happening. Statistically this means that while it will not happen often, it will happen at some point.
I think the problem arises from the wide spread belief that DNA testing is infallible and provides concrete proof of a persons guilt/innocence - it does not.
DNA evidence is just that, evidence, and should be regarded as such in court. If DNA testing along with collaborating evidence indicates the person is guilty, then they probably are - or vice versa. If there is evidence that points against the DNA results, one should not automatically assume that the DNA results are correct.

Not as unlikely as you might think...

[Sfuerst]

As Terry Pratchett says:
"Million to one chances happen nine times out of ten."

Statistical problem can be overcome

[divec]

Right, 37 million to one is not very big odds when you're doing 245 billion independent tests.
If the probability of a false positive in any individual test is p, then the probability of conducting n tests without getting any false positives is (1-p)^n. As pointed out, this means that if enough tests are done you'll almost certainly convict an innocent person. If you have two crimes with DNA evidence that is only this reliable, then more than likely some innocent person in the UK would test guilty.
Actually, it's worse than this because people don't have independent DNA - they're likely to be distantly related. This makes false positives even more likely.
If there are n people and you want the probabilility that any of them test positive to be less than x then you need
1 - (1-p)^n < x, which is nearly the same as 1 - p*n < x. So to be fairly sure that nobody in the world falsely tests positive you need p to be less than about 1 in 80 billion.

P(false positive) -> 1 as n -> oo

[divec]

The probability of a false positive match approaches 1 as the number of samples approaches oo.

P(false positive) = 1 - P(no false positives)
= 1 - (P(correct answer))^n
= 1 - (1-p)^n
-> 1 as n -> oo.

This is ignoring the probability of a false negative; this is very low since only one person can commit a crime!

DON'T THEY KNOW ANYTHING ABOUT STATISTICS?

[Nicolas MONNET]

This is so basic, I can't even believe it! I can't believe peoples lives are decided on such a weak mathematical basis!

If the chance of a match between two random DNA samples is 1/37.10^6, and they have 660000 samples in their database, then the likelihood -- assuming their system does'nt give false positives, which I doubt -- of a database match is ... 1.78% !!! We don't know how much DNA tests they make each year, but it's porbably well over a thousand, wich leads to over 10 false positives a year!

Americans find that "mind blowing"? Minboggling stupidity, if you ask me