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Why did the U.S. prison population increase so much?

Why did the U.S. prison population increase so much?
© Songman Kang, Hanyang University
The U.S. prison population has skyrocketed in recent years.
The number of prisoners in the federal and state prisons increased from 196,000 in 1970 to 1,570,000 in 2010 (a more than 700 percent increase). Even after accounting for the population increase, the incarceration rate has grown more than four-fold.
What are potential explanations for this drastic increase? First, the number of crimes increased during the 1970s and 1980s, leading to an increased number of criminals to be punished. Advances in policing strategy and technology may have improved the efficiency of police, helping them to improve their “catch” rate. Lastly, state and federal governments introduced a series of get-tough sentencing strategies which greatly increased the probability and length of incarceration.
Criminologists Steven Raphael and Michael Stoll’s in-depth analysis reveals that the recent prison population boom was largely driven by tougher sentencing and post-release supervision policies, instead of actual changes in individuals’ criminal behavior.
First, they find that the average length of incarceration for each type of offense substantially increased. (For example, the average length of incarceration for rape increased by 74 percent, assault by 40 percent and larceny by 48 percent between 1984 and 1998.)
Tougher sentencing laws led to increases in the length of prison sentence and the actual time served by inmates. Many state governments replaced their indeterminate sentencing system, in which judges had greater discretion on the length of sentences, by usually-more-strict determinate sentencing, in which a pre-determined formula computes the recommended length of sentences based on the severity of current offense and prior criminal records. Also, many states introduced “truth-in-sentencing” laws which required criminals to serve at least 85 percent of their sentence before becoming eligible for parole, which greatly reduced the probability of early prison release.
Second, they find that the probability of incarceration for less-serious crimes has sharply increased. Between 1984 and 2002, the number of prison admissions for violent and property offenders increased by about 70 percent and 30 percent, while prison admissions for drug offenders increased by more than 550 percent. Third, more strict post-release supervision policies led to a large increase in prison entries. The parole failure rate nearly doubled between 1980 and 2003, and more than 40 percent of all prison entries in 2002 were due to parole violation.
Raphael and Stoll note that the increases in the probability and length of incarceration explain 80 to 85 percent of the prison population increase, while the change in individuals’ criminal behavior played a more limited role. In sum, the rapid prison population increase in the U.S. over the last few decades was mostly the result of deliberate policy interventions. In the next article, we will examine the gains and losses associated with this policy experiment.


  • Raphael, S., and Stoll, M. (2009). Why Are So Many Americans in Prison? In S. Raphael and M. Stoll (Eds.), Do Prisons Make Us Safer? The Benefits and Costs of the Prison Boom(pp. 27-72). New York: Russell Sage Foundation.
© Songman Kang, Hanyang University
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Economics of Crime

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