Date of Award


Document Type


Degree Name

Doctor of Psychology (PsyD)


Graduate Department of Clinical Psychology

First Advisor

Mary Peterson, Ph.D.

Second Advisor

Alexander Millkey, Psy.D.

Third Advisor

Wayne Adams, Ph.D.


This study contributes to the psychometric validity of the psychological tests most frequently used to determine competency to stand trial for people with intellectual disabilities. First, the relationship between The MacArthur Competence Assessment Tool (MacCAT-CA) and the Competence Assessment to Stand Trial for Defendants with Intellectual Disabilities (CAST-MR) was analyzed, including their respective determination of competency for currently adjudicated adults with intellectual disabilities. Second, the relationship between performance on the Malingered Incompetence Legal Knowledge test (MILK), a new measure designed to evaluate malingering by people with intellectual disabilities in a legal context, and the Test of Memory Malingering (TOMM) was explored. Additionally, this study contributes to the development of norms for both the MacCAT-CA and the MILK in a population with intellectual disabilities. Results demonstrate that was not significant agreement between the Mac CAT-CA and the CAST-MR in determining adjudicative competency in the study population. The lack of convergent validity between these two commonly used measures raises questions about test validity and whether individuals with intellectual disabilities are held to a lower standard for adjudicative competence. Further, a significant correlation between the TOMM and the MILK suggests that evidence of exaggerated cognitive impairments does suggest feigned ignorance of legal knowledge. The evidence from this study suggests that CST evaluations with an ID population results in different findings based on the measure that the examiner chooses. Consequently, adherence to appropriate and standardized measures is needed in forensic psychology to ensure the quality of the evaluation.

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