Junk Science In the Courtroom

An Expert? Prove it!

Lawyers and scientists have completely different ways of discovering truth. The lawyers’ way is dueling witnesses. This is as good as any in determining which of two people is lying about a police shootout. It is no good in determining whether a hair sample matches that of the murder defendant or whether Vioxx caused a heart attack. Do heavy objects fall faster than light ones? Scientists answer with an experiment. A court would answer by having the jury hear from two experts, one saying yes, the other saying no. It would make as much sense to have the jury watch a medieval jousting contest between the two witnesses.

“The adversarial system is premised on the theory that if you have two liars testifying, the truth will come out,” says David Bernstein, a professor at George Mason University. In a forthcoming article for the Iowa Law Review, he critiques what he calls “connoisseur testimony.” A witness says that X causes Y and backs up the statement not with an objective test but with his diplomas and his years of experience. You could use connoisseur testimony to convict someone of witchcraft.

Asbestos plaintiffs claim to have spots on their lungs. Do they? A recent report by the Manhattan Institute notes that plaintiff physicians find abnormalities in 95.9% of X rays; nonaligned radiologists find them in 4.5%. Here’s a radical thought on how to get at the truth. Take 50 supposedly abnormal films and shuffle them with 50 taken from people never exposed to asbestos but matched in sex, age and smoking habits. Now ask the plaintiffs’ expert to pick out the abnormal ones.

A witness for the prosecution testifies that he can match hair samples with 98% accuracy? Forget the credentials. The judge should make him pass a blind test.

It won’t happen. When it comes to science, judges are steeped in a long tradition of welcoming junk into the courtroom.

What I understand of the standards of evidence for science in the courtroom really bothers me -- particularly as a former engineer. Our current legal system seems to be ill-equipped at allowing truth-seeking science into the courtroom and instead seems to rely as much on theatrics and pedigrees more than anything else.

I was particularly disturbed by this when we were reading Damages, a book about a medical malpractice case, for one of my classes. In the case (which is a real case), the lawyers on both sides go on "mining expeditions" to find medical experts who will support their clients' position rather than trying to examine evidence to try to understand what really happened. (The case was about a baby who was born with severe developmental problems.)

As much as the lack of scientific rigor in the case bothered me, I was alarmed even more deeply when my professor didn't seem to find anything wrong with the way lawyers use science in the courtroom. I find it tragic that the law has such a low standard for evaluating objectively knowable information.

(HT Todd Zywicki)