It still isn’t clear what caused the big drop in U.S. crime rates in the last two decades, but it wasn’t mass incarceration, says the Brennan Center for Justice at New York University School of Law, Brennan’s Inimai Chettiar writes in The Atlantic. In a report, “What Caused the Crime Decline?,” Brennan examined 14 popular theories. The report finds that the growth in incarceration was responsible for between 0 and 10 percent of the drop in crime in the 1990s. Since then increases in incarceration have had essentially no effect on crime.
So what did contribute to the decrease? Brennan cites “a vast web of factors, often complex, often interacting, and some unexpected.” Among them: a growth in income, changes in alcohol consumption, the aging population, decreased unemployment, increased numbers of police officers, and the introduction of CompStat. The legalization of abortion and unleading of gasoline may also have played some role. Concludes Brennan: “In aggregate, the fourteen factors we identified can explain some of the drop in crime in the 1990s. But even adding all of them together fails to explain the majority of the decrease.”