Uses and Abuses of Empirical Evidence in the Death Penalty Debate

53 Pages Posted: 30 Jan 2006

See all articles by Justin Wolfers

Justin Wolfers

University of Michigan at Ann Arbor - Department of Economics; University of Michigan at Ann Arbor - Gerald R. Ford School of Public Policy; The University of Sydney - Discipline of Economics; Brookings Institution - Economic Studies Program; Peterson Institute for International Economics; National Bureau of Economic Research (NBER); IZA Institute of Labor Economics; Centre for Economic Policy Research (CEPR); CESifo (Center for Economic Studies and Ifo Institute); Kiel Institute for the World Economy

John J. Donohue

Stanford Law School; National Bureau of Economic Research (NBER)

Multiple version iconThere are 4 versions of this paper

Date Written: January 2006

Abstract

Does the death penalty save lives? A surge of recent interest in this question has yielded a series of papers purporting to show robust and precise estimates of a substantial deterrent effect of capital punishment. We assess the various approaches that have been used in this literature, testing the robustness of these inferences. Specifically, we start by assessing the time series evidence, comparing the history of executions and homicides in the United States and Canada, and within the United States, between executing and non-executing states. We analyze the effects of the judicial experiments provided by the Furman and Gregg decisions and assess the relationship between execution and homicide rates in state panel data since 1934. We then revisit the existing instrumental variables approaches and assess two recent state-specific execution moratoria. In each case we find that previous inferences of large deterrent effects based upon specific samples, functional forms, control variables, comparison groups, or IV strategies are extremely fragile and even small changes in specifications yield dramatically different results. The fundamental difficulty is that the death penalty - at least as it has been implemented in the United States - is applied so rarely that the number of homicides that it can plausibly have caused or deterred cannot be reliably disentangled from the large year-to-year changes in the homicide rate caused by other factors. As such, short samples and particular specifications may yield large but spurious correlations. We conclude that existing estimates appear to reflect a small and unrepresentative sample of the estimates that arise from alternative approaches. Sampling from the broader universe of plausible approaches suggests not just reasonable doubt about whether there is any deterrent effect of the death penalty, but profound uncertainty - even about its sign.

Keywords: execution, capital punishment, homicide, crime, death penalty

JEL Classification: K14, K42

Suggested Citation

Wolfers, Justin and Donohue, John J., Uses and Abuses of Empirical Evidence in the Death Penalty Debate (January 2006). IZA Discussion Paper No. 1949, Available at SSRN: https://ssrn.com/abstract=879765 or http://dx.doi.org/10.2139/ssrn.879765

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