Legal Admissibility of the Competence Assessment for Standing Trial for Defendants with Mental Retardation (CAST-MR)

The Competence Assessment for Standing Trial for Defendants with Mental Retardation (CAST-MR) was developed to assess competence to stand trial in defendants with Intellectual Disability. Although it remains the only validated instrument for this population, previous research has suggested it is rarely used by forensic examiners, a finding our survey of legal cases confirms. Initial validation studies provided some support for the instrument's reliability and validity. However, in both these and subsequent studies, there were significant limitations with respect to the size and representativeness of study samples, and therefore the associated interpretation of scores, such that questions remain as to whether the tool adequately assesses competence to stand trial in this population. In this paper, we review the research on the CAST-MR, discuss the strengths and limitations of the instrument, and debate its legal admissibility.