An Impact Assessment of Machine Learning Risk Forecasts on Parole Board Decisions and Recidivism

A close approximation to a natural, randomized experiment was used to evaluate the impact of the forecasts on parole release decisions. A generalized regression discontinuity design was used to evaluate the impact of the forecasts on recidivism. The forecasts apparently had no effect on the overall parole release rate, but did appear to alter the mix of inmates released. Important distinctions were made between offenders forecasted to be re-arrested for nonviolent crime and offenders forecasted to be re-arrested for violent crime. The balance of evidence indicates that the forecasts led to reductions in re-arrests for both nonviolent and violent crimes. The evaluation concludes that risk assessments based on machine-learning forecasts can improve parole release decisions, especially when distinctions are made between re-arrests for violent and nonviolent crime. (Publisher abstract modified)