The usefulness of a crime harm index: analyzing the Sacramento Hot Spot Experiment using the California Crime Harm Index (CA-CHI)

Abstract

This study introduces the California Crime Harm Index (CA-CHI) and explores in what context a Crime Harm Index is a meaningful measure, comparing crime count outcomes to the CA-CHI. I decouple violent and property crime to determine when harm is a better indicator of reduction rather than counts. The Sacramento Hot Spot Experiment (SHSE) was a 90-day randomized controlled trial testing the effectiveness of 15-minute high-visibility police patrols to high crime and call for service hot spots. In this paper, I translate Part I crimes counts into the CA-CHI. I conduct t tests for both Part I crime and CA-CHI between experimental and control hot spots. Effect sizes are calculated to observe the differences between Part I crime and CA-CHI. Part I crimes were decoupled into violent and property crime and similarly analyzed. The SHSE’s effect size using the decoupled violent and property crime CA-CHI as the outcome measures was less than when the Part I crime counts were analyzed. Violent crime had too small a sample size to properly analyze. The impact of the SHSE is not as strong when using the CA-CHI to evaluate crime outcomes compared to crime counts. The reduction in harm is driven largely by the property crime reductions. The sensitivity of the CA-CHI is reduced when violent crime is excluded. The CA-CHI or any derivation of a CHI may not be a useful tool when using a harm index on a small study, dataset, or municipality.