Integrating base rate data in violence risk assessments at capital sentencing.

Prediction of violence in capital sentencing has been controversial. In the absence of a scientific basis for risk assessment, mental health professionals offering opinions in the capital sentencing context are prone to errors. Actuarial or group statistical data, known as base rates, have proven far superior to other methods for reducing predictive errors in many contexts, including risk assessment. Actuarial follow-up data on violent recidivism of capital murderers in prison and post release have been compiled and analyzed to demonstrate available base rates for use by mental health experts conducting risk assessments pertaining to capital sentencing. This paper also reviews various methods for individualizing the application of base rates to specific cases.