Quantifying CAHOOTS: Measuring a mobile crisis response program's impact on police response through call diversion and prevention.

Mobile Crisis Response Programs (MCRPs) have emerged as alternatives to police for emergency mental and behavioral health calls, yet their effectiveness in diverting calls from police remains contested. CAHOOTS (Crisis Assistance Helping Out On The Streets), the United States' longest-running MCRP, has been subject to widely varying ad hoc diversion rate estimates, from 3 to 20%. We use a systematic difference-in-differences design to estimate the causal effects of CAHOOTS on police call volume by introducing three estimators. The Substitution Diversion Rate (SDR) quantifies MCRP responses that directly replace police responses and estimates the rate at 18% for CAHOOTS. Our results indicate that in addition to substituting for police response, CAHOOTS was associated with reductions in police-handled call volume consistent with a prevention effect. The Prevention-adjusted Diversion Rate (PDR) accounts for both call substitution and prevention, and we estimate it at 23% for CAHOOTS. Last, the Overlapping-mandate Diversion Rate (ODR) quantifies the proportion of mutually answerable calls handled by an MCRP. We estimate CAHOOTS' ODR at 50%. Our findings provide evidence that MCRPs significantly reduce police response call volume through direct substitution and likely incident prevention.