Improving the Detection of Feigned Knowledge Deficits in Defendants Adjudicated Incompetent to Stand Trial

Abstract

Malingering is relatively common in criminal forensic evaluations as base rates of malingering have ranged from 20% to 30%. Given that the most prevalent criminal forensic evaluation is the assessment of competency to stand trial, the assessment of feigning during competency evaluations is necessary for accurate findings. Most of the response style literature focuses on feigning mental health symptoms, but in competency evaluations, individuals may attempt to feign legal knowledge deficits in order to be found incompetent to stand trial. The current investigation includes two studies: 195 students instructed to simulate feigned mental illness or incompetence to stand trial and one using a sample of 130 state psychiatric hospital residents who had been adjudicated incompetent to stand trial. The purpose of the study was to evaluate the Inventory of Legal Knowledge’s (ILK; Musick & Otto, 2010) ability to detect individuals who are feigning legal knowledge deficits. Classification utility statistics, including sensitivity, specificity, positive predictive power, and negative predictive power are provided for each cut-score on the ILK beginning with a cut-score of 24 (which is the lower end of the range of chance) are provided. The current cut-score of 47 provided in the professional manual of the ILK was shown to create a large number of false positives and suggests that modifications to this cut-score are required.