Daubert, cognitive malingering, and test accuracy.

Daubert v. Merrell Dow Pharmaceuticals (1993) held that trial judges should permit expert scientific testimony only when "the reasoning or methodology underlying the testimony is scientifically valid, and ... properly can be applied to the facts in issue." Vallabhajosula and van Gorp ("V & vG," 2001) have suggested that when the Daubert standard is applied to tests for malingered cognitive deficits, courts should deem admissible only results that meet this mathematical standard: assuming a pretest probability of .3, a "positive" score on the malingering test should yield a posttest probability of at least .8. This paper shows that V & vG's criterion may lead to misunderstandings about the kind of information maligering measures provide. After reviewing cases that have discussed both the Daubert decision and malingered cognitive deficits, this paper uses data from the Test of Memory Malingering (T.N. Tombaugh, 1996) to provide a general characterization of the mathematical properties of malingering measures. The paper then describes how pretest knowledge about malingering is combined with knowledge about a test's performance to generate a posttest probability of malingering. The results can help mental health experts respond to Daubert-inspired challenges to conclusions based on malingering measures.