Since 2011, California has significantly reformed its criminal justice system, reducing the size of its prison population, with no effect on violent crime and only marginal impacts on property crime statewide. The COVID-19 pandemic furthered decarceration as the state reduced state prison and jail populations to slow the spread of the virus. Concerns emerged that releases under the auspices of COVID mitigation harmed public safety. A new study explored this notion and found no consistent relation between COVID-19-related jail decarceration and violent or property crime at the county level in the state.

The study, by researchers at the University of California (UC) Irvine and the University of Arizona, is published in the Journal of Contemporary Criminal Justice. Their work is promoted by the Crime and Justice Research Alliance, which is funded by the National Criminal Justice Association.

"California's efforts to reduce overcrowding as a way to limit the spread of COVID-19 reduced the correctional population more severely and abruptly than any of the state's previous decarceration reforms," according to Charis E. Kubrin, professor of criminology, law, and society at UC Irvine, who led the study. "Concerns about what impact these actions would have on crime rates were widespread, and although violent and property crime in large cities declined during the pandemic, homicide and car theft rose significantly."

Because these increases mirrored national trends, it was unclear whether California's pandemic-related decarceration efforts were responsible. In this study, researchers sought to determine whether COVID-19 jail downsizing measures were related to crime trends in the state, estimating the effect of the measure on crime in the state's 58 counties and isolating the impact of decarceration on crime from other shocks affecting the state as a whole. They examined monthly average daily jail population counts from January 2013 to December 2021, and county-level monthly crime data during the same period; COVID-19 decarceration occurred from January through December 2020.

The study did not find a consistent relation between COVID-19 jail decarceration and crime at the county level, suggesting that downsizing, on average, did not drive crime increases statewide.

Among the study's limitations, the authors note that because they used a synthetic control adaptation, the treated and synthetic series did not reflect the fully treated and completely untreated versions of county crime rates that are generally produced via synthetic controls. The authors also note they measured COVID-19 mitigation efforts only from March through December 2020—a relatively short period—in order to minimize the effects of crime associated with summer 2020 protests following the murders of Breonna Taylor, George Floyd, Jacob Blake, and others.

"These limitations reveal how challenging it is to identify decarceration's potential effect from any one factor during one of the most dynamic and challenging periods the state, as well as the country as a whole, experienced," notes Bradley J. Bartos, assistant professor of government and public policy at the University of Arizona, who coauthored the study. "Nonetheless, our findings offer insights that can inform future criminal justice innovations."