How objective are forensic experts when they are retained by one of the opposing sides in an adversarial legal proceeding? Despite long-standing concerns from within the legal system, little is known about whether experts can provide opinions unbiased by the side that retained them. In this experiment, we paid 108 forensic psychologists and psychiatrists to review the same offender case files, but deceived some to believe that they were consulting for the defense and some to believe that they were consulting for the prosecution.The study is behind a paywall, so I don't have the details. Of course they found bias. It is nice to see someone try to quantify the bias. Here is also a law professor article on expert bias.
I asked psychologist psychologist Ken Perlmutter of Palo Alto, under oath, whether there was any evidence supporting the correctness of his opinion in any of the 750 evaluations he had done. He admitted that there was none, and that all 750 evaluation could have been poorly done, for all anyone knows. So of course he was biased. He even refused to start his evaluation until he was able to call Commissioner Irwin H. Joseph on the phone to ask him what outcome he wanted. Perlmutter should have lost his license for what he did. And he would have, if his record had been fairly examined.