Are There Experts on Dangerousness?
This chapter applies the final three admissibility factors — probative value, helpfulness, and prejudicial impact — to expert prediction testimony. Despite false-positive rates approaching 50 percent, prediction testimony should usually be considered probative because, contrary to critics’ insinuation with their coin-flipping analogy, both clinical and actuarial predictions produce results better than chance selection would. Furthermore, in contrast to culpability testimony, we at least have error rate information about predictions, which provides the fact finder with a way of gauging its worth. Prediction testimony is also generally helpful, at least when it avoids ultimate issue language, because it identifies risk factors that laypeople might not otherwise consider. The chapter concludes that where prediction testimony is most likely to fail in evidentiary terms, is with respect to the fourth factor, prejudicial impact. When the government proffers expert testimony that someone who has just been convicted of charged with an offense is dangerous, it is merely confirming what the fact finder already strongly suspects. When this testimony is presented in clinical, as opposed to actuarial, form, even aggressive rebuttal evidence normally has minimal impact on the fact finder. Thus, the chapter argues that the decision as to whether clinical expert testimony on dangerousness will be presented should be left up to the subject of the prediction. This subject first rule is analogous to the well-known character evidence rule, which bars evidence of bad character, despite its probativeness on the issue of whether the defendant committed an offense, unless and until the defendant opens the door by presenting evidence of good character.
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