Most of the benefits of prison come from incapacitation rather than deterrence.

Judge against the empirical criminology and economics literature as of December 2024. True if the main reviews and studies conclude that most of the crime reduction from imprisonment comes from incapacitation rather than general or specific deterrence (e.g. the marginal deterrent effect of longer sentences is small, while incapacitation accounts for most of the measured effect). Mostly true if the literature leans that way but with notable caveats or disagreement. Mixed if it is genuinely split, or if the answer depends heavily on which margin is studied (sentence length versus certainty of punishment). Mostly false if the claim is stated as settled when the evidence is inconclusive, or if it takes a narrow finding (e.g. about sentence enhancements only) as general. False if the evidence shows deterrence accounts for most of the benefits.

Set before the research began.

1. E1 Read National Academies of Sciences, Engineering, and Medicine (National Research Council committee report) · 24 April 2014

   “In this regard, one of our most important conclusions is that the incremental deterrent effect of increases in lengthy prison sentences is modest at best.”

2. E2 Criminal Deterrence: A Review of the Literature American Economic Association (Journal of Economic Literature) · March 2017

   “Evidence in favor of deterrence effects is mixed. While there is considerable evidence that crime is responsive to police and to the existence of attractive legitimate labor-market opportunities, there is far less evidence that crime responds to the severity of criminal sanctions.”

3. E3 Deterrence in the Twenty-first Century: A Review of the Evidence Carnegie Mellon University, Heinz College (Research Showcase @ CMU); hosted by Nevada Legislature exhibit archive · 2013

   “Thus, the case for crime prevention benefits of measures requiring lengthy prison sentences such as California’s three-strikes law must rest on incapacitation.”

4. E4 Incapacitation as a Strategy for Crime Control: Research Findings (research brief) U.S. Department of Justice, National Institute of Justice · December 1983

   “The most striking finding is that incapacitation does not appear to achieve large reductions in crime.”

The National Research Council report (E1) concludes that the added deterrent effect of increases in lengthy prison sentences is "modest at best", and the Carnegie Mellon review (E3) says the crime-prevention case for lengthy sentences "must rest on incapacitation". The Journal of Economic Literature review (E2) describes the evidence on deterrence as mixed: it finds far less evidence that crime responds to the severity of sanctions, but considerable evidence that crime responds to police, which points to a caveat about deterrence through policing. The 1983 NIJ brief (E4) adds a caveat that incapacitation itself does not appear to achieve large reductions in crime, and none of the sources measures what share of prison's total effect comes from incapacitation, so the literature leans toward the claim without settling it.