Validity, Interrater Reliability, and Measures of Adaptive Behavior: Concerns Regarding the Probative Versus Prejudicial Value

The question as to whether the assessment of adaptive behavior (AB) for evaluations of intellectual disability (ID) in the community meet the level of rigor necessary for admissibility in legal cases is addressed. AB measures have made their way into the forensic domain, in which scientific evidence is put under great scrutiny. Assessment of ID in capital murder proceedings has garnished a lot of attention, but assessments of ID in adult populations also occur with some frequency in the context of other criminal proceedings (e.g., competence to stand trial, competence to waive Miranda rights), as well as eligibility for social security disability, social security insurance, Medicaid/Medicare, government housing, and postsecondary transition services. As will be demonstrated, markedly disparate findings between raters can occur on measures of AB even when the assessment is conducted in accordance with standard procedures (i.e., the person was assessed in a community setting, in real time, with multiple appropriate raters, when the person was younger than 18 years of age), and similar disparities can be found in the context of the unorthodox and untested retrospective assessment used in capital proceedings. With full recognition that some level of disparity is to be expected, the level of disparity that can arise when these measures are administered retrospectively calls into question the validity of the results and, consequently, their probative value.