TY - JOUR AU - Donohue,John J.,III AU - Wolfers,Justin TI - Uses and Abuses of Empirical Evidence in the Death Penalty Debate JF - National Bureau of Economic Research Working Paper Series VL - No. 11982 PY - 2006 Y2 - January 2006 UR - http://www.nber.org/papers/w11982 L1 - http://www.nber.org/papers/w11982.pdf N1 - Author contact info: John J. Donohue Stanford Law School Crown Quadrangle 559 Nathan Abbott Way Stanford, CA 94305 Tel: 650/721-6339 E-Mail: donohue@law.stanford.edu Justin Wolfers Business and Public Policy Department Wharton School, University of Pennsylvania 3620 Locust Walk Room 1456 Steinberg-Deitrich Hall Philadelphia, PA 19104-6372 Tel: (215) 898-3013 Fax: (215) 898-7635 E-Mail: jwolfers@wharton.upenn.edu AB - 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 morartoria. In each case we find that previous inferences of large deterrent effects based upon specific examples, functional forms, control variables, comparison groups, or IV strategies are extremely fragile and even small changes in the 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. ER -