Incarceration: Increased incarceration had some effect, likely in the range of 0 to 10 percent, on reducing crime in the 1990s. Since 2000, however, increased incarceration had a negligible effect on crime.
State Success: A number of states, including California, Michigan, New Jersey, New York, and Texas, have successfully reduced their prison populations while crime continues to fall.
Other Factors: Increased numbers of police officers, some data-driven policing techniques, changes in income, decreased alcohol consumption, and an aging population played a role in the crime decline. In particular, the report finds CompStat is associated with a 5 to 15 percent decrease in crime. The report also includes new information on the effects of unemployment, the death penalty, and other theories on crime.
During the 25 years since 1990, incarceration rates have exploded – almost doubling in size – and added about 1.1 million additional people behind bars. During that same time, crime rates have been cut almost in half. Using an economic model that accounts for the diminishing returns of extremely high levels of incarceration and includes the latest 13 years of data, the report bolsters past research suggesting increased incarceration had little impact on crime rates, but finds an even smaller impact on crime.
“This report amplifies what many on the left and the right have come to realize in recent years: mass incarceration is not working. It simply isn’t necessary to reduce crime,” said Inimai Chettiar, director of the Brennan Center’s Justice Program and author of the executive summary. “The prison explosion has been very expensive. A better use of public resources would be improving economic opportunities, supporting 21st century policing practices, and expanding treatment and rehabilitation programs, all of which have proven records of reducing crime without incarceration’s high costs.”
“This groundbreaking empirical analysis from the Brennan Center shows that, on examination, the easy answers do not explain incarceration’s effect on crime,” wrote Dr. Joseph E. Stiglitz, a Nobel laureate in economics and University Professor at Columbia University, in the foreword. “This report presents a rigorous and sophisticated empirical analysis performed on the most recent, comprehensive dataset to date.”
Read the full report, What Caused the Crime Decline?
Read an excerpt of the report in The Atlantic.