DETERRENCE: Why the Studies Have Failed to Produce Reliable Results

Two researchers at the University of Pennsylvania’s Wharton School, Professors Justin Wolfers (pic­tured) and Betsey Stevenson, recent­ly explained why decades of stud­ies have failed to show a reli­able deter­rent effect from the death penal­ty. The authors cit­ed a 2012 report from the National Academy of Sciences, con­clud­ing that the deter­rence stud­ies of the past 30 years ​“should not influ­ence pol­i­cy judg­ments about cap­i­tal pun­ish­ment.” Wolfers and Stevenson explain why these stud­ies can­not be relied on regard­ing whether the death penal­ty deters mur­der:
–the death penal­ty is applied extreme­ly rarely (1 exe­cu­tion in 500 mur­ders), which makes empir­i­cal study of its impact dif­fi­cult to mea­sure;
–homi­cide rates fluc­tu­ate for rea­sons com­plete­ly unre­lat­ed to cap­i­tal pun­ish­ment (homi­cide rates tend to rise and fall rough­ly in uni­son across states, regard­less of whether they have the death penal­ty);
–a more vig­or­ous use of the death penal­ty like­ly occurs at the same time as oth­er crim­i­nal jus­tice changes, and it is impos­si­ble to sep­a­rate the effects of the death penal­ty from the effects of these changes; and
–most impor­tant­ly, there is no evi­dence on how poten­tial mur­der­ers per­ceive the risk of exe­cu­tion if they are caught, which is key to deter­min­ing whether cap­i­tal pun­ish­ment is a deterrent.

The authors also cit­ed the research of Wolfers and John Donohue of Standford, who con­clud­ed, ​“There’s ​‘not just ​“rea­son­able doubt” about whether there is any deter­rent effect of the death penal­ty, but pro­found uncer­tain­ty.’” They fur­ther con­clud­ed, ​“Overall, the [National Academy] panel’s con­clu­sions are a wel­come cor­rec­tive to a debate in which polit­i­cal­ly expe­di­ent, yet imper­fect, find­ings have attract­ed greater atten­tion than those rare moments of humil­i­ty when we social sci­en­tists admit what we don’t know.”

(B. Stevenson and J. Wolfers, ​“The Death-Penalty Represents a Market Failure,” Bloomberg News, June 11, 2012). See Deterrence and Studies. Listen to DPIC’s pod­cast on Deterrence.