Field Notes

concept

Deterrence

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Deterrence is the idea that threatened legal punishment reduces offending: would-be offenders weigh the expected cost of punishment against the crime’s reward, and a higher expected cost means less crime. The expected cost has two components — the certainty of being caught and punished, and the severity of the punishment if caught — and the central empirical finding of the last two decades of criminology is that the two are not interchangeable. Daniel Nagin’s 2013 review for Crime and Justice, the standard modern synthesis, concludes that the evidence “that certainty of apprehension, not the severity of the ensuing legal consequence, is the more effective deterrent” is now strong enough that lengthy prison sentences and mandatory minimums “cannot be justified on deterrence.”1

Certainty beats severity

The certainty-side evidence comes from several independent designs: police-presence variation, sanction-certainty experiments, and perceptual studies of offenders. What they share is a consistent sign: raising the probability of apprehension measurably reduces crime, while raising the statutory penalty for those already apprehended does little or nothing. Nagin attributes the divergence partly to how punishment is perceived: severity enters a potential offender’s calculation only through an imagined future consequence, discounted and uncertain, while the visible presence of enforcement changes the immediate environment in which the decision is made. A policy implication follows directly: homicide clearance rates — the objective side of certainty for the most serious crime — matter more for deterrence than sentence length, which makes the long US clearance decline a deterrence problem in itself.

The severity-side null

Severity research keeps returning null or fragile results. The National Research Council’s 2012 review of capital-punishment deterrence studies found the entire literature “not informative”: studies did not account for the deterrent effect of the non-capital sanctions that accompany capital regimes, used models sensitive to arbitrary specification choices, and could not credibly separate the death penalty’s marginal effect from the life sentences that would otherwise be imposed.2 Donohue and Wolfers reached a similar conclusion about the econometric death-penalty studies that had reported large deterrent effects: the estimates collapse under small changes to the sample or specification.3 The strongest comparative design is Zimring, Fagan, and Johnson’s natural experiment comparing Singapore and Hong Kong — culturally and economically similar cities with opposite execution policies — which found no visible effect of Singapore’s much higher execution rate on homicide trends.4 Durlauf and Nagin’s review of the imprisonment-crime relationship found that the crime-reducing effect of incarceration comes overwhelmingly through incapacitation, not deterrence: locking people up prevents crimes by physically removing offenders, not by discouraging others.5

Levitt’s influential decomposition of the 1990s US crime drop identified four factors that mattered — more police, rising imprisonment, the waning of the crack epidemic, and legalized abortion — and explicitly placed the death penalty among six factors that did not.6 Farrell and colleagues’ cross-national study of the crime drop found declines across countries with wildly different penal policies, which is hard to reconcile with any sentencing regime having driven them.7

The effective margin is enforcement, not sentencing

The positive deterrence findings concentrate in two enforcement-side interventions. Police numbers: Chalfin and McCrary’s review concludes US cities are underpoliced — the marginal dollar spent on policing returns more in reduced victimization than it costs, with the effect concentrated on serious violent crime.8 Mello’s study of COPS hiring grants found the funded officers reduced violent and property crime at low fiscal cost.9 And Chalfin, Hansen, Weisburst, and Williams’s quasi-experimental estimates show each additional officer prevents roughly 0.1 homicides, with the benefit roughly twice as large for Black victims, while also generating more low-level, racially disparate arrests — the benefit and the cost of the same margin.10 Focused deterrence strategies are the second: Braga, Weisburd, and Turchan’s meta-analysis of pulling-levers programs, which concentrate enforcement attention and social services on the small number of groups driving violence, found moderate, statistically significant crime reductions across twenty-four evaluations.11

The policy-relevant contrast is therefore not “tough versus lenient” but where the marginal deterrent is purchased: more severity is cheap to legislate and nearly worthless, while more certainty is expensive — officers, investigators, clearance capacity — and is where the returns lie. Mass incarceration sits on the wrong side of that trade: it buys incapacitation at scale while the certainty margin, which the evidence says matters more, is left underfunded.

  1. Daniel S. Nagin, “Deterrence in the Twenty-First Century,” Crime and Justice 42 (2013): 199-263, doi:10.1086/670398; saved copy. The quoted conclusions are from the abstract and pp. 254-256. ↩

  2. National Research Council, Deterrence and the Death Penalty (Washington, DC: National Academies Press, 2012), doi:10.17226/13363. The “not informative” finding is at p. 2. The publisher’s full text blocked automated download; the report’s conclusions are stated in its own summary. ↩

  3. John J. Donohue III and Justin Wolfers, “Uses and Abuses of Empirical Evidence in the Death Penalty Debate,” Stanford Law Review 58 (2005): 791-846. ↩

  4. Franklin E. Zimring, Jeffrey Fagan, and David T. Johnson, “Executions, Deterrence, and Homicide: A Tale of Two Cities,” Journal of Empirical Legal Studies 7, no. 1 (2010): 1-29, doi:10.1111/j.1745-9133.2010.00653.x. ↩

  5. Steven N. Durlauf and Daniel S. Nagin, “Imprisonment and Crime: Can Both Be Reduced?” Criminology & Public Policy 10, no. 1 (2011): 13-54, doi:10.1111/j.1745-9133.2011.00680.x. ↩

  6. Steven D. Levitt, “Understanding Why Crime Fell in the 1990s: Four Factors That Explain the Decline and Six That Do Not,” Journal of Economic Perspectives 18, no. 1 (2004): 163-190, doi:10.1257/089533004773493485. ↩

  7. Graham Farrell, Nick Tilley, and Andromachi Tseloni, “Why the Crime Drop?” Crime and Justice 43 (2014): 421-490, doi:10.1086/678081. ↩

  8. Aaron Chalfin and Justin McCrary, “Are U.S. Cities Underpoliced? Theory and Evidence,” Review of Economics and Statistics 100, no. 1 (2018): 167-186, doi:10.1162/REST_a_00694. ↩

  9. Steven Mello, “More COPS, Less Crime,” Journal of Public Economics 172 (2019): 174-200, doi:10.1016/j.jpubeco.2019.05.002. ↩

  10. Aaron Chalfin, Benjamin Hansen, Emily K. Weisburst, and Morgan C. Williams Jr., “Police Force Size and Civilian Race,” American Economic Review: Insights 4, no. 2 (2022): 139-155, doi:10.1257/aeri.20200292; saved copy. ↩

  11. Anthony A. Braga, David Weisburd, and Brandon Turchan, “Focused Deterrence Strategies and Crime Control: An Updated Systematic Review and Meta-Analysis of the Empirical Evidence,” Criminology & Public Policy 17, no. 1 (2018): 205-250, doi:10.1111/1745-9133.12353. ↩

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