Instruments for Assessing Competency to Stand Trial: How Do They Work?

Abstract

Previous research has demonstrated that the Competency Screening Test (CST) and a revised version of the Georgia Court Competency Test (GCCT-MSH [Mississippi State Hospital]) accurately predict competency decisions made by forensic examiners. We used internal consistency analyses, item analyses, and factor analyses to determine how the instruments predict the competency criterion. These analyses failed to reveal a clear basis for the predictive power of the CST. We were unable to establish correlates of the better predictors or to label the item clusters that emerged from the factor analyses. In contrast, analyses of the GCCT-MSH revealed a straightforward internal structure that comprised three factors. The factor that predicted staff decisions most accurately (Specific Legal Knowledge) consisted of items that were relevant for the individual defendant's case and that appeared to tap psychopathology as well as intellectual ability. This study highlights the need for investigators to examine the empirical relationships between psychological constructs and defendants' legally relevant functional abilities.