Intellectual Disability and Adjudicative Competence Evaluations

Psychology, Public Policy, and Law | 2025, Vol. 31, No. 3, p. 234-245

Intellectual Disability and Adjudicative Competence Evaluations: A Detailed Review of an Often-Overlooked Population

Mary Elizabeth Wood; Department of Psychiatry & Behavioral Sciences, Division of Psychology, Vanderbilt University Medical Center; Department of Psychology & Philosophy, Sam Houston State University

Haley Potts; Department of Psychiatry & Behavioral Sciences, Division of Psychology, Vanderbilt University Medical Center

Stella Wang; Department of Psychiatry & Behavioral Sciences, Division of Psychology, Vanderbilt University Medical Center

Research has indicated that individuals with intellectual disability represent a relatively small but meaningful subset of defendants referred for adjudicative competence evaluations. While scholars have consistently argued that this population is unique and requires special consideration in terms of the competency assessment and treatment process, little is known about this population overall and/or the relative effectiveness of the uniquely tailored interventions recommended in the literature. The current study, an archival analysis of 117 court-ordered adjudicative competence evaluations, aimed to address this gap by focusing exclusively on a known group of defendants with intellectual disability. The results revealed a significantly lower base rate of opined competence (18.8%) relative to the larger population of defendants referred for competency evaluations (i.e., historically between 70% and 80%). Nearly one-quarter of the sample was opined unrestorable, which was associated with significantly lower measured intelligence (d = 0.61 and 0.91) and adaptive behavior scores (d = 1.04) than their counterparts. These results add to a very limited body of research on this subset of defendants. Implications are discussed in terms of systemic considerations, with a particular emphasis on the need for appropriate services for this subset of defendants, as well as a commitment to research on the efficacy of these interventions.

Adjudicative competence, intellectual disability, unrestorable

“Previous research suggests that defendants with ID represent a small but meaningful subset of those referred for adjudicative competence evaluations and forensic inpatient treatment… The base rate of competence among this subset of defendants is unclear, as previous studies are limited in quantity and methodological strength, and the estimates from those studies have varied widely. Despite this uncertainty, prior studies have found a consistent relationship between ID and a reduced likelihood of restoration to (or attainment of) competence), even with tailored training. The present study was therefore designed to systematically describe the characteristics of, and associated outcomes for, adjudicative competence examinees with a known diagnosis of ID” (p. 236).

The authors conducted “an archival analysis of data coded from court-ordered adjudicative competence evaluations” completed between 2014 and 2021 in a large metropolitan area in the southeastern United States. The final sample included 117 evaluations of unique defendants, all diagnosed with intellectual disability (ID), identified through a systematic review of clinic records after excluding juveniles, provisional ID diagnoses, malingering cases, and evaluations conducted prior to a statutory change. Data were coded from forensic reports on demographics, diagnoses, legal variables, and psycholegal opinions, including competency and restorability determinations. Prior intellectual functioning and adaptive behavior data were extracted when available, with analyses limited to scores from comprehensive Wechsler or Stanford–Binet measures; the “earliest reported score” was used and adjusted for the Flynn Effect to reduce practice effects. Competency opinions were coded into six jurisdiction-specific categories and collapsed into conceptually meaningful groupings for analysis. Two independent coders achieved “excellent” interrater reliability (ICC = .99), and analyses were primarily descriptive, supplemented with t tests and chi-square analyses conducted in SPSS (p. 236-238).

Defendants with intellectual disability (ID) constitute a distinct and particularly vulnerable subgroup within adjudicative competence evaluations. The authors describe the primary finding as striking, noting that “the base rate of competence in this sample was astonishingly low (18.8%), and nearly one-quarter was considered unrestorable during the initial evaluation.” Although lower competence rates are conceptually consistent with ID as a “qualifying mental disease/defect,” the authors argue that “the degree of this difference suggests other factors may also be at play,” beyond individual cognitive limitations. They further highlight that, contrary to prior literature, there were “few differences between competent and incompetent groups, including on measures of functioning (i.e., IQ and AB scores),” which they attribute in part to restricted range, small subgroup sizes, and measurement limitations. In contrast, the more meaningful distinction was restorability: “arguably, the more important distinction is whether an incompetent defendant is unrestorable,” with unrestorable defendants showing lower intellectual and adaptive functioning and moving more quickly to case disposition (p. 241-242).

Although unrestorable defendants showed lower intellectual and adaptive functioning, caution is warranted in interpreting these data. While group differences were observed, “scores must be considered alongside the broader clinical picture,” and reliance on a single metric is discouraged. Determining future competence based on one test score is described as “arguably problematic and potentially misleading,” given measurement error, practice effects, and the heterogeneity of presentations among individuals with ID. Psychometrically valid measures are positioned as tools that should “inform, but not entirely dictate, opinions regarding competency and/or the capacity to attain competency in the future” (p. 241).

Structural features of the jurisdiction are highlighted as potentially shaping outcomes. The evaluation process operates through “a wholly separate process” for defendants with ID, involving distinct statutory guidance and disability-specific services. On its face, this approach aligns with recommendations for “tailored interventions, differing levels of service intensity, and alternatives to prosecution,” yet its real-world impact remains unclear in the absence of outcome data. The existence of a separate pathway may also implicitly signal a “low likelihood of restoration and/or the ineffectiveness of treatment,” increasing the likelihood of early unrestorability opinions. At the same time, enhanced training for attorneys may have improved identification and referral, with data suggesting “potentially better identification of defendants with ID, especially in the higher range of functioning, without any associated decrement in ‘successful’ referrals or ‘hit rates.’” Overall, these findings underscore that unrestorable defendants with ID may be “categorically distinct from defendants considered unrestorable for other underlying reasons,” raising unresolved clinical, legal, and policy challenges (p. 241-242).

“The current study raises some important public policy questions, especially surrounding the relative impact of a distinct procedure/ process for defendants with ID who may be incompetent to stand trial. Though theoretically ideal and consistent with broad, systems-level recommendations to address the competency crisis (see e.g., Callahan & Pinals, 2020; Murrie et al., 2023), it is unclear whether the system works as intended, and the efficacy of modified restoration training programs remains unknown. Ideally, data on rearrest and subsequent evaluation and/or hospital referrals would help to ascertain longer-range outcomes.

Perhaps, the more important policy consideration, however, is how to address the disproportionately high rate of unrestorable defendants in this sample (23.9%). Unrestorable defendants had significantly lower intellectual and adaptive functioning scores, half were charged with at least one violent offense, and one-quarter was diagnosed with a comorbid psychotic spectrum disorder. In Jackson v. Indiana (1972), the United States Supreme Court was instructive, holding that defendants cannot be held longer than the time needed to determine whether there is a likelihood of attaining competence. While civil commitment may be pursued, this may not be available in all jurisdictions. In Tennessee, for example, judicial commitment for individuals with ID is only available through the court, and only following a finding of incompetence. It is these cases that create the most significant difficulty for courts, as prosecution is not an option nor is continued confinement/incarceration, given the unlikelihood of attaining competence, and the criteria for judicial commitment—which often require imminent threats/danger—inherently reflects a distinct issue from competency. The complexity of these issues is such that input from the public, professionals, and policymakers at all levels is needed.

It is worth noting that the recommendation for tailored services is hardly novel and/or that the need to address broader clinical issues in the context of adjudicative competence evaluations has been one of the more obvious byproducts of the competency crisis. Indeed, Murrie et al. (2023) recently argued for better triage and service matching to navigate the problems arising from increasing referrals, higher rates of incompetent defendants, and reduced resources (e.g., hospital beds), which is not unlike the recommendations of Callahan and Pinals (2020) and/or the work of Policy Research Associates and SAMHSA (2022). For incompetent and unrestorable defendants with ID, however, alternatives within the legal system (e.g., specialty courts, supervised release provisions, and placement in special needs facilities) are not an option. Legal decision makers are urged to consider creative solutions to address this gap. Though complex, given the competingforcesofrespect forautonomyandindependent decision making alongside the inherent need to manage/mitigate potential risks/needs (both to the individual and society), it is not unreasonable to expect that our criminal legal system—which has been tasked with addressing nearly every other social ill/problem (e.g., substance abuse, homelessness, criminal conduct, delinquency, and truancy)—could make strides toward filling this obvious and costly gap” (p. 242).

“The present study has several limitations that are important to review. The first is that the sample was relatively small, and the evaluations were all conducted in the same jurisdiction by the same team of evaluators. Regarding the jurisdiction issue, generalizability may be limited due to local practices or policies, including that misdemeanants have historically been excluded from competency training/services, as well as the distinct process for defendants with ID relative to other forensic examinees. While the latter arguably reflects a more effective and conceptually sound approach/model, it does limit comparisons to other systems without similar options for defendants with ID. In addition, there is evidence to suggest that distinct jurisdictional practices have systematically increased referral rates for defendants with ID, which is unlikely to generalize elsewhere.

Unfortunately, outcome data following referral for competency restoration/training were not available. These data are crucial to assess the effectiveness (or lack thereof) of remediation with this population (Anderson & Hewitt, 2002; Wood et al., 2019; P. Zapf, 2013). Of those referred for outpatient training, 9.5% were convicted, though it is unclear whether (and to what extent), this reflects the rates of restoration to competence versus other factors resulting in a greater likelihood of dismissal of charges. Only one-quarter of the sample was convicted, which is considerably less than the 60% conviction rate of misdemeanants in the same jurisdiction and during the same timeframe (Tansey et al., 2021). This suggests defendants with ID may be treated differently, independent of competency. Further research is needed to explore this possibility, as this could provide a mechanism for better and/or earlier diversion efforts, including options that bypass the forensic evaluation system/process altogether” (p. 242).