Intelligence is a poor predictor of nonrestorability of competence to stand trial.

Criminal defendants found incompetent to stand trial (IST) may only be committed for competency restoration if their restoration success is considered likely and when this aim can be met within a "reasonable" period of time. In this study, we evaluated the predictive validity and test accuracy of standardized intelligence testing on the classification of nonrestorability in a sample of 293 male patients adjudicated IST and committed for inpatient restoration. At 90 days, 17.0% of cases with FSIQ scores within one standard deviation of the mean were unrestored, and nonrestoration rates increased with each additional FSIQ standard deviation decrement to 29.5%, 38.8%, and 59.5%. Time-to-event analyses found that whereas half of patients with FSIQ scores of 56 or higher would be predicted to be restored within 64 days, the median restoration timeline was 145 days for patients with FSIQ scores of 55 or below. Positive predictive values associated with the range of possible FSIQ scores were uniformly low at modeled nonrestoration prevalence rates of 5%, 15%, and 25%, rarely exceeding chance levels. We conclude that although FSIQ scores are relevant to predictions of nonrestorability, particularly when scores are at least three standard deviations below average, the accuracy of individual FSIQ-based predictions of nonrestorability are limited.