Experts and Trials III:  More Noise 

 In my previous two posts  here  and  here , I discussed some of the game-theoretic reasons why lawyers' choice of experts in cases might only add noise to the process.  In this post, I will draw on my own experience on a jury, evaluating expert witnesses, to speak to further pitfalls in our system. 

 First, some background on my case: I was on a jury for a medical malpractice trial, essentially deciding whether a tumor, which later killed the patient, should have been spotted on an earlier X-ray.  The "standard of care" to which we were to hold the doctors in question was a completely relative metric: Did the doctors provide the level of care "expected" from the "ordinary" practicing radiologist.  Predictably, radiologists testified for both the plaintiff and the defense, each claiming that it was obvious that the defendants violated/met the relevant standard of care. 

 My position, as might be expected given my earlier posts, was that these two experts, on net, provided very little information on the culpability of the defendants.  For all I knew, 99% of qualified doctors could have believed these doctors were negligent, or not negligent - how would I ever know?  Since my prior was uninformative in this case, I had no choice but to find for the defendants for lack of evidence in either direction. 

 My fellow jurors, however, had far stronger opinions.  Many tended to believe or disbelieve an expert witness for irrelevant reasons.  For instance, the physical attractiveness, speech pattern, and general "likeability" played a great role.  Furthermore, the experts usually made or lost ground on their ability to explain the basics of the science underlying the issue at hand - the mechanics of an X-ray, for instance - to the jury.  Of course, these basics were not in dispute by any party in the case.  And, as any student at Harvard University knows, a witness's ability to clearly and succinctly explain the basics need not be related at all to her expertise in the field!  That these facts influence juries should be of no surprise to anyone familiar with trials; the existence of an entire industry of "jury consultants," the legal equivalent of marketing professionals, should be evidence enough that these issues of presentation matter a great deal. 

 Finally, even after the experts presented their cases, the priors of some jurors seemed to greatly affect their opinions of the case.  Though jurors are screened for such biases, the test cannot be perfect.  I often found jurors relating personal experiences with radiologists as evidence for one side or another.  Given my arguments above about the lack of information from experts, perhaps it is not surprising that priors mattered as they did, but this seemed to further add noise into the process. 

 In the end, I supported my jury's decision in this case.  But I could not help feeling that it was simply by random chance, by a peculiar confluence of misinterpretation and biases, that we had reached the right decision.