Homogenous Base Rates for Malingering in Neuropsychological Examination of Litigants

Abstract

Base rates for malingering are often obtained and averaged across multiple clinicians who apply heterogeneous methods for detection (Mittenberg et al., J Clin Exp Neuropsychol 24: 1094−1102, 2002; Young, Psychol Inj Law 8: 200–218, 2015). Our aims of obtaining homogenous base rates included the following: (a) evaluation of all our legal cases in accordance with the guidelines set forth in the position papers by both the National Academy of Neuropsychology and the Association for Psychological Advancement in Psychological Injury and Law, (b) minimal variation between our comprehensive neuropsychological examinations, and (c) determination of base rates of failed effort in 150 consecutively examined legal cases in one medical setting. To assess the various levels of volitional exaggeration, we introduced four gradations of poor effort definitions, which relied on performance validity tests (PVTs). A comparison between two consecutive samples of 75 litigants indicated less frequent poor effort with increasingly more conservative criteria. In our analysis of a subset of litigants who sustained traumatic brain injuries (N = 115), the four base rates for mild versus moderate-severe TBI groups were equivalent for the two more lenient malingering definitions but varied for the two more conservative definitions. Specifically, for the mild TBI cases investigated, the percentage of three PVT failures (or one PVT failure significantly below chance) arrived at 3.4 %. Our final aim was to compare the base rates of poor effort that were obtained with PVTs to the base rates of emotional and physical symptom endorsement, which were obtained with symptom validity tests (SVTs). No significant correlations emerged in this analysis. The discussion emphasizes the relatively lower base rates of poor effort found in the convenience sample studied in neuropsychological evaluations relative to the higher estimates in the literature (40 +/− 10 %, Larrabee et al., Clin Neuropsychol 23: 841–849, 2009) but not others based on comprehensive review (Young, Psychol Inj Law 8: 200–218, 2015).