Don't Confuse me with the Facts: Common Errors in Violence Risk Assessment at Capital Sentencing

The life and death context of a capital risk assessment requires a comprehensive forensic evaluation. Mental health professionals routinely testify regarding future dangerousness in capital proceedings but too often limit assessment to DSM-IV diagnoses and criminal history without integrating empirical and actuarial data from other sources. Given the grave magnitude of a capital risk assessment both for the defendant and society, methodological and conceptual errors of this type must be avoided. This article will describe violence risk-assessment errors made by mental health professionals testifying at capital sentencing. Observed errors include inadequate reliance on base rates, failure to consider context, susceptibility to illusory correlation, failure to define severity of violence, overreliance on clinical interview, misapplication of psychological testing, exaggerated implications of antisocial personality disorder, ignoring the effects of aging, misuse of patterns of behavior, neglect of preventive measures, insufficient data, and failure to express the risk estimate in probabilistic terms.