Certainty of Punishment Deters Crime

Scholars have published over 100 empirical studies in the last three decades testing for the deterrent effect of punishment on criminal activity. Most support the existence of a deterrent effect for both the risk of imprisonment and longer prison time.

  • A U.S. National Academy of Sciences panel estimated a few years ago (1993) that a 50 percent increase in the probability of incarceration prevents twice as much violent crime as a 50 percent increase in the length of incarceration.

  • More recently, using state data for 1940 and 1950, researchers found a 50 percent boost in the chance of imprisonment prevents three to five times as many murders as a 50 percent increase in prison time for murderers.

  • A greater risk of execution (most states used the death penalty then) also deters murder.

    A greater imprisonment risk discourages twice as many robberies as the same boost in prison time, while risk and time have about the same impact on aggravated assault.

    Source: Isaac Ehrlich and Zhiquiang Liu, "Sensitivity Analyses of the Deterrence Hypothesis: Let's Keep the Econ in Econometrics," Journal of Law and Economics, April 1999.

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