Diminishing Returns: Incarcerating More People Brings Increasingly Smaller Crime Reduction Benefits

The US prison population has grown sharply over the last 40 years, reaching 496 prisoners for every 100,000 people, up from 150 in 1972.  All this growth took place in spite of declining crime rates.  A newly released report by the Brennan Center for Justice examines the relationship between incarceration and crime.  More specifically, the authors ask: "How does an ever-increasing prison population change how incarceration affects crime over time?"


The researchers collected data on most of the major factors thought to affect crime rates for all 50 states from 1980 to 2013 in order to test 14 popular theories for the crime decline over the last 20 years.  These theories focus on criminal justice policies (increased incarceration, increased policing, use of the death penalty, enactment of right-to-carry laws), economic factors (unemployment, growth in income, inflation, consumer confidence), and social and environmental factors (decreased alcohol consumption, aging population, decreased crack use, legalization of abortion, decreased lead in gasoline).

Using multivariate regression analysis, the researchers found that:

  • Increased incarceration at today's levels has a negligible crime control benefit.  Increased incarceration has had little effect on the drop in violent crime in the past 24 years.  It accounted for about six percent of the reduction in property crime in the 1990s but since 2000, it has had no effect on property crime to speak of.
  • CompStat, a policing approach that helps police gather data used to identify crime patterns and target resources, is responsible for a 5-15 percent decrease in crime where it was introduced.
  • Certain social (aging population), economic (changes in income), and environmental factors (decreased alcohol consumption) have also played a role in the crime drop.
  • There is no evidence that the death penalty, or right-to-carry laws, have had any measurable effect on crime.


The authors conclude that incarceration is a crime control strategy with diminishing returns: when prisons are used sparingly (low incarceration rate), incarceration is reserved for those offenders commit the most crime and/or the most serious crimes.  As the use of incarceration increases, the additional people who get caught in the criminal justice net are people who pose relatively little threat to society.  "This effect makes each additional person incarcerated offer fewer crime control benefits."

Read more:
http://fivethirtyeight.com/features/the-imprisoners-dilemma/
http://www.brennancenter.org/publication/what-caused-crime-decline

TeachingwithData.org resources:
Prisoners per Capita (http://www.nationmaster.com/graph/cri_pri_per_cap-crime-prisoners-per-capita)
Bureau of Justice Dynamic Data Tools (http://www.bjs.gov/index.cfm?ty=daa)
CrimeStat III Crime Mapping Tool (http://www.icpsr.umich.edu/CrimeStat/)
Frederique Laubepin

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