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What Caused the Crime Decline? exam­ines one of the nation’s least under­stood recent phenom­ena – the dramatic decline in crime nation­wide over the past two decades – and analyzes vari­ous theor­ies for why it occurred, by review­ing more than 40 years of data from all 50 states and the 50 largest cities. It concludes that over-harsh crim­inal justice policies, partic­u­larly increased incar­cer­a­tion, which rose even more dramat­ic­ally over the same period, were not the main drivers of the crime decline. In fact, the report finds that increased incar­cer­a­tion has been declin­ing in its effect­ive­ness as a crime control tactic for more than 30 years. Its effect on crime rates since 1990 has been limited, and has been non-exist­ent since 2000.

More import­ant were vari­ous social, economic, and envir­on­mental factors, such as growth in income and an aging popu­la­tion. The intro­duc­tion of CompStat, a data-driven poli­cing tech­nique, also played a signi­fic­ant role in redu­cing crime in cities that intro­duced it.

The report concludes that consid­er­ing the immense social, fiscal, and economic costs of mass incar­cer­a­tion, programs that improve economic oppor­tun­it­ies, modern­ize poli­cing prac­tices, and expand treat­ment and rehab­il­it­a­tion programs, all could be a better public safety invest­ment.