How That 'Extra .9%' Could Ward Off a Zombie Apocalypse

netbuzz writes "The questioner on Quora asks: 'When is the difference between 99% accuracy and 99.9% accuracy very important?' And the most popular answer provided cites an example familiar to all of you: service level agreements. However, the most entertaining reply comes from a computer science and mathematics student at the University of Texas, Alex Suchman. Here's his answer: 'When it can stop a Zombie Apocalypse.'"

Comments

Statistics 101

[blackicye]

An example we were given in my Intro to Stats module once upon a time used the Space Shuttle Program.

The numbers following the decimal point are very important when it might mean the difference between a Space Shuttle failing catastrophically instead of leaving / returning through the atmosphere intact.

And the vast differences in manufacturing costs between a 99.9%, 99.99% and 99.999% fault tolerant component and why
it would be necessary in the bigger picture of the complete system.

Re:Statistics 101

[Solandri]

Actually, the Challenger disaster hinged on a different failure in statistics. Originally the SRB segments were mated with 2 O-rings. Inspection of the SRBs after launch revealed the O-rings were failing at a higher than expected rate. So to mitigate the risk they redesigned the system and... added a 3rd O-ring. The reasoning was that if a single O-ring had a (say) 1% chance of failure, then two would have a .01^2 = .01% chance of failure, and three would have a .01^3 = .0001% chance of failure.

Unfortunately, that reasoning only works when the failures are independent events. If a single event (like cold weather) can cause the failure of one O-ring, it can also cause the failure of the other O-rings, so that failure mode is not independent. And your chance of all three O-rings failing is closer to 1% instead of 0.0001%.

Same thing happened at the Fukushima nuclear plant. They had something like a dozen diesel generators under the theory that even if a few failed to start, it was highly unlikely that all would fail to start. They completely missed the possibility that a single common event could cause all the generators to fail the same way.

Re:Statistics 101

[digitig]

Which is why you'd make the O-rings out of different compounds, and install no set with all the same type.

Which still doesn't eliminate dependent failures, because the failure of one O-ring increases the stress on the next O-ring (particularly the burst of pressure as the first O-ring fails).

Locate the diesel generators in 2 or 3 power houses around the site.

Which doesn't eliminate dependent failures when the failures are due to a contaminated fuel delivery.

2+ server rooms on site with replication between them (with additional replication off-site).

Which doesn't eliminate dependent failures when the failures are due to common software running on all sites.

But how much resource do you throw at the problem? Its easy for us after the events to decide if NASA should have used O-rings of differing compounds or Fukashima have multiple power houses on different levels.

For that you could call me in. Working that out what I do for a living.

Re:Statistics 101

[suutar]

The key factor is that the trait being tested is rare; only one in 500 people has it. In this case, the false positives can still be (substantially) more frequent than true positives.

Say you test 50,000 people. 100 have it, 49,900 don't. Of the 100 who have it, there will be 99 correct 'yes' results and one incorrect 'no' result. And of the 49900 who don't have it, there will be 49401 correct 'no' results and 499 incorrect 'yes' results.

So total, we have 598 'yes' results. But 499 of those are false positives, which is 83.4444%; only 16.5555% of the folks who test positive are really positive.

You've got cancer!

[complete loony]

A better answer; False positive medical tests.

Re:That's not the question

[Cryacin]

Well aren't you the genius.

The only difference between genius and insanity is that all the voices get along.

Re:Just Let It Die

[wonkey_monkey]

Just Let It Die

I'm trying, but it just keeps coming back!

This zombie fad is getting worn out. Just stop it, stop referencing it, stop producing zombie-related media, just STOP.

Alternatively, you could stop trying to be the arbiter of what is good and worthy and just indulge in the media you do enjoy. I'm very sorry* if you feel marginalised by those who have an interest in all things undead and shambling, but no-one's actually forcing to watch The Walking Dead or Jersey Shore.

*I'm not really

Re:That's not the question

[Joce640k]

Start by looking at yourself in a mirror. Maybe you'll see something whooshing over your head.

Re:That's not the question either

[tehcyder]

It's probably of deep significance for cultural anthropologists where this zombie meme came from, but I'm actually sick&tired of the whole thing. Zombies == instant unfunny guarantee.

What's worrying is not so much that there's a stupid meme, but that people can even begin to try to rationalise it and behave as though it could actually happen.

Personally, I just think it's feeding the insane "survivalist" mentality that is spreading like a virus through the US. Oh, wait...

Re:That's not the question

[AK Marc]

Yeah, because if you don't follow Vampire Canon, the vampire FBI will hunt you down and turn you.

Re:That's not the question

[MaskedSlacker]

I wish such an agency existed. Then we wouldn't have that sparkling bullshit.

Re:That's not the question

[deimtee]

It's not a virus, it's a parasitic protozoan that is common in cats.
It's called toxoplasmosis gondii and it makes men violent and women horny.
Rats also get it, and it makes them attracted to the smell of cat piss.

Re:That's not the question either

[Sarten-X]

...people can even begin to try to rationalise it and behave as though it could actually happen.

It's also an educational opportunity. I occasionally do mentoring, and I've used zombies as a good example for a worst-case scenario for emergency preparedness. It provides a good narrative to cover a wide variety of situations where everything's gone wrong, without entering into a ridiculous movie-plot-specific series of impossibly unlikely events. By starting out with the assumption that we're already in a worst-case scenario, where the survivor is one of only a few to survive an epidemic, it's not a terribly large stretch to assume that the car won't start, or that there's a storm coming, or that an earthquake has broken gas lines, and the survivor can't rely on government services.

Speaking of how impossible a zombie is, the zombie apocalypse also provides some ironically humane ways to discuss epidemiology, biology, medicine, and ethics, because pop-culture zombies are a convenient infection without suffering. The actual conversion process is rarely a focus in stories, and once the zombie is a zombie, they're too mindless to even fear harm. They just keep wandering, not even bothering to eat regularly... which brings us to discussing chemistry and thermodynamics.

Personally, I just think it's feeding the insane "survivalist" mentality that is spreading like a virus through the US. Oh, wait...

Jokes aside, we don't have any Communists or Nazis today to worry about, or Confederates, or British, or Spanish, or Visigoths, or Persians, or even rival tribes. We do have terrorists to fear, but there aren't any terrorists likely to launch a full occupation of the US. The survivalist mentality has always been here, but now we don't have any looming evil that we need to survive. While minor emergencies (such as those requiring the aforementioned preparedness) may happen, the barbarians aren't at the gate. They're in their living rooms, shouting insults into their XBox.