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"Having performed thousands of similar hair examinations over the previous 10 years, the FBI agent told the court, there had been only eight or 10 times when ha

"Having performed thousands of similar hair examinations over the previous 10 years, the FBI agent told the court, there had been only eight or 10 times when hairs from two different people were so similar that he could not tell them apart" At worst this is a 1% error rate, at best 0.1%. Scientific validity aside, I find it unbelievable this was not considered reasonable doubt.

no_gravity 11y ago
> At worst this is a 1% error rate If those 1000 pairs of hairs really were from different, randomly choosen people. But we don't know the quality of that sample. Maybe the examiner looked at 1000 pairs of hairs, 10 looked similar to him and those 10 were from different heads, while the 990 that looked different were from the same head. That would give an error rate of 100%. Even if we assume there were no errors in the sample, then we still don't know anything about the correlation between the judgement of the examiner and reality. Maybe he randomly considers one in 100 pairs of hairs to look similar. So while yes, the error rate would be 1%, his judgement would have absolutely no informative value. It would be as good as throwing dice.
rogeryu 11y ago
So take two people, take two hairs of each, pick two random hairs of those two, and compare them. I guess this could work out quite well. Do this for 1000 pairs of two different people, and 10 will fail, so that is 1%. This is how I understand it now. It's not that he says that he compares one hair to those 1000, and then still was sure to be able to keep them apart. That was how I first read it. For a good comparison, he should have used a line-up. Take one hair from 100 persons with similar hair color and use that as test sample. If he was still able to tell which was from the same person, he would have a case.
mbroshi 11y ago
Kirk Odom notwithstanding, presumably they were only doing hair anlysis of suspects that were already presumed guilty. This is not a random sample.
notahacker 11y ago
The comments section adds an interesting counterpoint to the Guardian's spin: he was also jailed on the evidence of the victim identifying his photograph, picking him out of an identity parade based on appearance and voice and testifying against him in court. Whilst DNA evidence has subsequently exonerated him, there were pretty good reasons for the jury at the time to consider the case proven beyond reasonable doubt that didn't involve placing too much faith in dubious "expert witness" testimony about hairs.
- ptaipale 11y ago
  Interesting that you get downvoted for saying that. There are good grounds to be somewhat suspicious of forensic evidence; however, my understanding is that technical evidence like this is usually far, far more reliable than e.g. eyewitness statements. Those are horribly unreliable, and experienced investigators (or should we say "investigators") are able to convince their witnesses of having seen things that did not really happen at all.
  - notahacker 11y ago
    Eyewitness statements aren't reliable (hell, I've given an eyewitness description that wasn't that reliable, judging by the reaction of the police officer who had just taken a statement from somebody else), but I'd see it quite hard for a court in a pre-DNA testing era not to have convicted when a reasonably certain and consistent testimony from a rape victim is supported by the supposed forensic experts at the time, especially not if the chief argument for the defence was a weak alibi offered by the accused's mother. Though since they've had DNA techniques sufficient to overturn the expert witness evidence for rather a long time now it's surprising it took this long to overturn.
- deleted 11y ago
  [deleted]
  - marrs 11y ago
    That's from the article. Parent is referring to the evidence that wasn't mentioned in the article.
marrs 11y ago
Well, scientists are like priests: their word is gospel to the unwashed masses. I suppose the defendant didn't have a scientist on his side who could identify and challenge the bullshit.
rhino369 11y ago
1% chance a person is innocent is probably roughly around the reasonable doubt standard. The problem is courts often misapply statistics. Prosecutors will often say in a case like this that there is a 100:1 chance that he did it because of the error rate. But they aren't applying Bayes Theorem.

no_gravity 11y ago

> At worst this is a 1% error rate If those 1000 pairs of hairs really were from different, randomly choosen people. But we don't know the quality of that sample. Maybe the examiner looked at 1000 pairs of hairs, 10 looked similar to him and those 10 were from different heads, while the 990 that looked different were from the same head. That would give an error rate of 100%. Even if we assume there were no errors in the sample, then we still don't know anything about the correlation between the judgement of the examiner and reality. Maybe he randomly considers one in 100 pairs of hairs to look similar. So while yes, the error rate would be 1%, his judgement would have absolutely no informative value. It would be as good as throwing dice.

rogeryu 11y ago

So take two people, take two hairs of each, pick two random hairs of those two, and compare them. I guess this could work out quite well. Do this for 1000 pairs of two different people, and 10 will fail, so that is 1%. This is how I understand it now. It's not that he says that he compares one hair to those 1000, and then still was sure to be able to keep them apart. That was how I first read it. For a good comparison, he should have used a line-up. Take one hair from 100 persons with similar hair color and use that as test sample. If he was still able to tell which was from the same person, he would have a case.

mbroshi 11y ago

Kirk Odom notwithstanding, presumably they were only doing hair anlysis of suspects that were already presumed guilty. This is not a random sample.

notahacker 11y ago

The comments section adds an interesting counterpoint to the Guardian's spin: he was also jailed on the evidence of the victim identifying his photograph, picking him out of an identity parade based on appearance and voice and testifying against him in court. Whilst DNA evidence has subsequently exonerated him, there were pretty good reasons for the jury at the time to consider the case proven beyond reasonable doubt that didn't involve placing too much faith in dubious "expert witness" testimony about hairs.

ptaipale 11y ago
Interesting that you get downvoted for saying that. There are good grounds to be somewhat suspicious of forensic evidence; however, my understanding is that technical evidence like this is usually far, far more reliable than e.g. eyewitness statements. Those are horribly unreliable, and experienced investigators (or should we say "investigators") are able to convince their witnesses of having seen things that did not really happen at all.
- notahacker 11y ago
  Eyewitness statements aren't reliable (hell, I've given an eyewitness description that wasn't that reliable, judging by the reaction of the police officer who had just taken a statement from somebody else), but I'd see it quite hard for a court in a pre-DNA testing era not to have convicted when a reasonably certain and consistent testimony from a rape victim is supported by the supposed forensic experts at the time, especially not if the chief argument for the defence was a weak alibi offered by the accused's mother. Though since they've had DNA techniques sufficient to overturn the expert witness evidence for rather a long time now it's surprising it took this long to overturn.
deleted 11y ago
[deleted]
- marrs 11y ago
  That's from the article. Parent is referring to the evidence that wasn't mentioned in the article.

marrs 11y ago

Well, scientists are like priests: their word is gospel to the unwashed masses. I suppose the defendant didn't have a scientist on his side who could identify and challenge the bullshit.

rhino369 11y ago

1% chance a person is innocent is probably roughly around the reasonable doubt standard. The problem is courts often misapply statistics. Prosecutors will often say in a case like this that there is a 100:1 chance that he did it because of the error rate. But they aren't applying Bayes Theorem.