Dostoevsky's Brother's Karamazov cleverly spoofs the careless inexpertness of what often passes for expert legal testimony.
Three medical experts are called to testify whether Dmitri Karamazov was sane or insane when committing the alleged murder of his father. Naturally, the experts all disagree, with each completely convinced of the incontrovertible truth of his own opinion. Expert 1 finds Dmitri insane because he looked to the left as he entered the courtroom. Expert 2 also finds Dmitri insane, but instead because he looked to the right. Expert 3 correctly finds Dmitri sane, but for the wrong reason that he stared straight ahead. And all three are absolutely sure Dimitri did commit the murder-which in fact he did not. Three blind mice.
Dostoevsky was recognized by Freud as the master of psychological thinking, but his love of psychology did not stop him from poking huge holes in its reliability. "One can draw from psychology whatever conclusions one likes. It all depends on whose hands it is in. I am speaking of excessive psychology, of a certain abuse of it."
He then demonstrates vividly just how the this abuse of psychology plays out in courtroom situations. The prosecutor on the case presents a brilliant, completely plausible psychological profile of Dmitri that proves beyond any shadow of doubt that he must have committed the crime. Then, based on the very same traits and facts, the defense attorney presents an equally brilliant, but completely opposite, psychological profile that proves beyond any shadow of doubt that Dmitri could not possibly have committed the crime. There is no gold standard that allows a jury to choose between the opposing speculations.
Dostoevsky uses a Russian proverb to explain this situation -- that psychology is a stick with two ends (equivalent to our sword that cuts both ways). He knew better than anyone that speculative psychological theorizing can be just as easily used to disguise the truth as to reveal it. A theory that seems completely plausible can be completely wrong.
Dostoevsky wrote 135 years ago, but his critique of forensic psychiatry and forensic psychology stands the test of time. The abuses he described still occur often today in just the way he described them. My experience as expert witness in hundreds of legal cases does not inspire much confidence in the way our legal system uses (and more often abuses) expert testimony.
Many factors contribute to experts generating heat, not light.
First off, many alleged experts are simply not really all that expert and say things that are just dead wrong. The filters meant to eliminate errant opinion and junk 'science' don't work.
Second, the adversarial system cultivates expert allegiance bias. Consciously or unconsciously, expert opinions are strongly influenced by who is paying the bill.
Third, juries often have to decide questions that are far beyond their competence. Which of the dueling experts to believe is more often determined by presentation skills and likability than the technical accuracy of the testimony.
Finally, the adversarial quality of the legal system demands that experts give black-and-white, yes-or-no answers to questions that often require a shades-of-gray, nuanced response. Even wise and unbiased experts mislead when they are forced to choose a yes or no when the best answer would be maybe or a little bit of both.
As it stands now, the expert testimony in many trials is pretty worthless. Each side presents an extreme set of opinions that in opposite ways distort the complex reality. The jury cancels them out or makes a pretty blind choice between them.
The system may be too embedded to reform, but a few simple changes would make a world of difference. To achieve neutrality and preserve nuance, experts should whenever possible be appointed by the court, not the warring sides. There should be a more rigorous way of establishing that they are indeed experts and are using methods of assessment that are reasonably reliable and well validated. Reports should document how the existing literature pertains to the facts of this case and the degree of confidence with which each opinion is rendered and why. Experts should be instructed to be cautious in their judgments, staying close to the facts and to the literature. I don't know is the most appropriate answer to many questions. Purely idiosyncratic speculation should be identified and treated as unreliable and essentially worthless.
Doing it right would much reduce the role of expert testimony in the legal system- probably a very good thing.
Allen Frances is a professor emeritus at Duke University and was the chairman of the DSM-IV task force.