New research from sociologist and criminologist Jason Robey in the University of Iowa College of Liberal Arts and Sciences examines what is driving declines in United States imprisonment rates and racial disparities in prison admissions.

Robey, an assistant professor in the Department of Sociology and Criminology, co-authored the study, “Why America’s prisons are shrinking and racial gaps are closing,” with Michael Light of the University of Wisconsin–Madison. The article was published in Nature Human Behaviour.

Using national data on recorded crimes, arrests, and prison admissions from 2000 to 2019, the researchers found that declines in imprisonment for violent and property offenses were driven primarily by falling crime rates rather than changes in policing or court processing. For Black Americans, the decline in prison admissions for violent offenses was entirely attributable to reductions in violent crime, according to the study.

Drug offenses followed a different pattern. The researchers found that reductions in arrests and changes in case processing contributed to declining drug-related prison admissions. Among Black Americans arrested for drug offenses, the likelihood of imprisonment fell by half between 2000 and 2019.

“Our previous research documented large reductions in incarceration rates for Black Americans, but an important question remained: Why are incarceration rates falling overall, and why are they falling faster for Black Americans?” Robey said. “This study helps provide answers by showing that the forces behind declining imprisonment differ substantially by type of offense.”

The findings suggest that the forces contributing to declining imprisonment rates differ from those that fueled the rise of mass incarceration, while highlighting the roles of both crime reduction and changes in criminal justice practices.