Heavier Sentences Do Deter Crime

Do prisons merely incapacitate criminals or deter them too? A new U.S. study of heavier sentences shows that prisons deter as well as isolate. Researchers studied the effects of California's Proposition 8, which imposed increased sentences for a select group of crimes.

Increased sentences have no incapacitation effect in the first few years because it adds years at the end of a criminal's regular sentence, not the beginning.

Yet crimes affected by increased sentences fell by 4 percent in the first year after passage of Proposition 8, and 8 percent three years later, a sizable effect.

Five to seven years later, the impact of the law increased, suggesting an incapacitation effect too.

Source: Daniel Kessler and Steven D. Levitt, "Using Sentence Enhancements to Distinguish between Deterrence and Incapacitation," Journal of Law and Economics, April 1999.

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