Hair the DNA Musical

Marquel, TPVs NYTimes Hair and Hair Style Correspondent, was doing his hair while reading the New York Times: DNA Analysis Exposes Flaws in an Inexact Forensic Science. Instances of wrongful imprisonment have made clear that microscopic hair analysis, a staple of forensics for years, was not as flawless as people had been led to believe.

Marquel read that the FBI has decided to be more strict with its experts. They can no longer say that they are certain or without doubt. Not only that, but when they have laboratory reports, they are not allowed to say there is only one in a thousand chance of another match. They must say there is a small amount in a pool of undetermined size. When you think about it, there’s not much certainty there.

Marquel decided to speak to one of the experts, one who had been dismissed recently for submitting fraudulent reports. It was the best I could do.

“So,” I began, “what’s the deal with hair? I thought if they found your hair on a body, you were a dead duck. Now, apparently, one hair resembles all the others.”

“Yes,” he answered, “it’s unfortunate. It turns out that all the science we used was never tested.”

“So people were convicted on the basis of theory?” I asked.

“I’m afraid so,” he answered.

“Theory that turns out erroneous?” I continued.

“Afraid so.” He confirmed. “You have to understand all hair looks different, but also similar. So when we found hair that looked exactly the same, we told that to the court.”

“But you also told the court that you were certain that there were no other similar hairs.” I said.

“Well, it was always true. If I had seen another hair like it, I would have said so.” He said.

“But since you only looked at occasional hairs, you never had a chance to do a survey of all hair, generally speaking, to see how many would look in fact identical.”

“That’s why they changed the rules.” He said.

“What are you supposed to do?” I asked.

“We can’t say we are certain, even with DNA. We give the odds with DNA. With all the rest, we’re supposed to say that we can include or exclude the sample from a pop…si…s…ze…wher…” he said.

“Huh?” I asked. He repeated the same sentence and started the same mumble and whisper at the end of the sentence. But I thought I knew what he said, because I had read the Times and the new FBI policy. So I continued, “are you saying you could include or exclude the sample from a population of unknown size?”

“Yes,” he said, “exactly. We can include or exclude the sample from a pop…mer…si…ation.”

“You seem to trail off there at the end.” I noted.

“It’s difficult to say” He said.

“Difficult in what way?” I asked.

“I guess out of habit. We are used to saying we are certain this came from the defendant and we can exclude any other possible individual. Or defendant’s hair matches that found on the body and no other hair could match it. To say that it comes from a pop…si…mer…lar…ation…is to say that we don’t know shit.” He said.

“I think you’re right. If I say that it matches the hair found, and that similar hair may exist in a population of unknown size, I’m basically saying I don’t’ know shit. Isn’t that right?” I asked.

“You’re exactly right” he said. “Actually I’m testifying tomorrow. You’re welcome to come. It’s a private case, so I’ve been hired by the defendant.”

I went to Centre Street the next morning and there he was testifying. The defense lawyer asked him whether the hair matched.

“Yes,” he stated, “but that kind of hair can be found in a pop…si…mer…lation…ilar.”

The prosecutor objected, the defense lawyer asked again, and got the same mumble. The judge intervened and said, “Objection overruled. He said the hair exists all over the population. It doesn’t prove a thing.”

The trial went on. The expert testimony was useless. The judge’s instruction was totally at odds with what the FBI had directed was proper scientific testimony. We met later.

“So how come you mumbled again?” I said.

“I told you, nobody with my experience can give that kind of testimony. It’s basically saying I found the hair. It looks like the other one, but I have no idea how many others might be identical. What kind of proof is that?”

“I think,” I said, “it’s the kind of proof the FBI wants. The question is why.”

“Oh, that’s easy,” he said. “There is no scientific basis for hair testimony. We’ve been using it for over a century and it turns out to be totally useless. But we can’t stop using it. Think. You have a redhead defendant. A brunette body. Red hair all over the body. Proof or no proof?

“I don’t know,” I said. “The Times was happy to report that even though scientific evidence isn’t as certain as it used to be, about half of all DNA tests prove the guy is guilty.”

“What about the other half?” he asked.

“I guess they weren’t guilty. But the Times didn’t mention what happened to them.” I said.

“Fifty fifty.” He said. “Well, we start football games on those odds, why not criminal trials?”

All I could say was, “why not?”

***

 Hair – The DNA Musical