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The ballooning national incarceration rate over the last few decades and the simultaneous decline in crime across the United States is by no means a case of cause and effect, according to a recent report by the Brennan Center for Justice.

Incarceration has long been a popular law enforcement tool in America: since 1970, the imprisonment rate has skyrocketed by more than 400 percent, and there are now 2.3 million Americans in prison or jail. The country is a world leader in incarceration rates—the U.S. has just 5 percent of the global population but 25 percent of its prisoners.

Even as imprisonment increased, crime decreased: the current crime rate is about half of what it was at its height in 1991, according to the report. Violent crime has fallen by 51 percent since 1991, and property crime by 43 percent.

After reviewing more than three decades of crime data, however, researchers concluded in the Brennan report that the explosion in incarceration had a limited influence on the crime rate.

Titled “What Caused the Crime Decline?” the report found that economic and environmental factors, including changes in income, decreased alcohol consumption and an aging population played a greater role in the national crime decline. The report also pointed to the efficiency of the policing program CompStat in the cities where it was introduced; increased numbers of police officers had a limited effect, they found.

The findings could inform policymaking, forcing bureaucrats to devise more effective, less expensive—and less discriminatory—ways of fighting crime.

“The toll of mass incarceration on our social and economic future is unsustainable,” Joseph E. Stiglitz, a Columbia University professor and the 2001 recipient of the Nobel Memorial Prize in Economic Sciences, wrote in the foreword of the report. “When high levels of incarceration provide scant public safety benefit, it is pointless to continue using—wasting—resources in this way. Instead, the country should shift priorities away from policies proven to be ineffective and focus our energies on truly beneficial initiatives that both reduce crime and reduce mass incarceration. The evidence presented here tells us that these are compatible goals.”

Read the full report here.