A systematic review with a meta-analysis included two quasi-experimental studies of pre-arrest redirection, with four independent samples. This study presents inconclusive findings for criminal (recidivism, as measured by new arrests) and mental health outcomes (improvements in mental health, as measured by use of services such as counseling, medication use, and hospitalization due to mental illness). However, in terms of cost savings or reductions associated with the implementation of pre-arrest diversion programs, that same study included a systematic review (10 studies) suggesting that pre-arrest diversion may result in overall cost savings [1].
Another systematic review evaluated the efficacy of post-charge redirection and post-incarceration redirection programs for people with mental health problems. In a total of 43 articles from which data were extracted, all were found to reduce recidivism, and almost all were found to reduce substance abuse. However, the evidence was strongest for the post-prosecution redirection programs [2].