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Does increasing the prison population reduce the crime rate?

We've all seen the charts showing the crime rate exploding in the US from the 60's through the 90's, then decreasing as we got tough on crime. Numerous articles point to this as a cause and effect - the crime rate went down because more criminals were behind bars. It sounds right, it seems like common sense. Except that crime rates started declining before many of the measures credited with reducing it (3 strikes) and had continued growing after other measures credited with reducing it (determinate sentencing). See the following charts.

Four Measures of serious violent crime

State prison population of offense type, 1980-2004

US Department of Justice, Bureau of Justice Statistics

[I can't tell if the graphs are still there - I get a message that there isn't enough memory space to display the picture. These are graphs from a government web site, thus paid for by public taxes and not subject to copyright limitations]

Some new studies suggest that the relation between imprisonment and crime rate is more complicated - it depends, for example, on the type of crime. The surge in prison populations has been largely driven by non-violent crimes, such as drug use. Putting more drug users in jail does not reduce violent crime, and may do the opposite, by driving up the black market cost of drugs and leading users to steal to feed their habit and dealers to fight to maintain their lucrative business. A recent study suggests the prison population can be significantly reduced without affecting the crime rate (Unlocking America, by the JFA Institute).

Another article describes studies that suggest there is an "inflection point" or "tipping point" (Do higher incarceration rates mean lower crime rates?, by Howard N. Snyder and Jeanne B. Stinchcomb, Oct. 2006 Corrections Today). Increasing the number of prisoners decreases the crime rate up to a point and then actually increases the crime rate after that. There could be a number of factors at work. Putting someone in prison destroys their chances for a job afterward. Combined with a virtual complete lack of help after release, this leads ex-cons to resort to crime again. Also, prison educates minor criminals on how to become worse, and embitters them.


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