"Incarceration has not been definitively shown to reduce crime rates. Bruce Western at Harvard University recently found that only 10 percent of the crime decline in the 1990s was due to increased use of incarceration.7 Between 1998 and 2007, states that had the greatest increases in incarceration rates did not necessarily see a corresponding drop in crime rates. Some states (Maryland Massachusetts, Nevada, New Jersey, New York, North Carolina, South Carolina, and Texas) lowered their incarceration rates and still experienced a drop in crime rates.8 Such uneven results do not support continued over-reliance on incarceration, particularly in a time of fiscal crisis."
Justice Policy Institute. Pruning Prisons: How Cutting Corrections Can Save Money and Protect Public Safety. Washington, DC, May 2009.