How Statistics Can Foul the Meaning of DNA Evidence

azoblue writes with a piece in New Scientist that might make you rethink the concept of "statistical certainty." As the article puts it, "even when analysts agree that someone could be a match for a piece of DNA evidence, the statistical weight assigned to that match can vary enormously, even by orders of magnitude." Azoblue writes: "For instance, in one man's trial the DNA evidence statistic ranged from 1/95,000 to 1/13, depending on the different weighing methods used by the defense and the prosecution."

Comments

1/13

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"Members of the jury, there's only a 1 in 13 chance that the defendant is actually the killer based on the DNA evidence. If the defendant were sitting in the jury with you, then there's an equal chance that it was any one of you. And since we can eliminate all 12 of you, that leaves only the defendant left over. So you must find the defendant guilty of all charges since he's the only one left out of 13 people. The prosecution rests."