Studies on Deterrence, Debunked

The Criminal Justice Legal Foundation has col­lect­ed many of the recent, con­tro­ver­sial deter­rence stud­ies, includ­ing ones by Hashem Dezhbakhsh, Paul H. Rubin, Joanna M. Shepherd, H. Naci Mocan & R. Kaj Gittings and oth­ers claim­ing a deter­rent effect to the death penal­ty. These stud­ies may be found here.

National Research Council, Deterrence and the Death Penalty

On April 18, 2012, the pres­ti­gious National Research Council of the National Academies released ​“Deterrence and the Death Penalty,” a report based on a review of more than three decades of research con­clud­ed that stud­ies claim­ing a deter­rent effect on mur­der rates from the death penal­ty are fun­da­men­tal­ly flawed. The report concluded:

The com­mit­tee con­cludes that research to date on the effect of cap­i­tal pun­ish­ment on homi­cide is not infor­ma­tive about whether cap­i­tal pun­ish­ment decreas­es, increas­es, or has no effect on homi­cide rates. Therefore, the com­mit­tee rec­om­mends that these stud­ies not be used to inform delib­er­a­tions requir­ing judg­ments about the effect of the death penal­ty on homi­cide. Consequently, claims that research demon­strates that cap­i­tal pun­ish­ment decreas­es or increas­es the homi­cide rate by a spec­i­fied amount or has no effect on the homi­cide rate should not influ­ence pol­i­cy judg­ments about cap­i­tal pun­ish­ment. (empha­sis added). 

Criminologist Daniel Nagin of Carnegie Mellon, who chaired the pan­el of experts, said, ​“We rec­og­nize this con­clu­sion will be con­tro­ver­sial to some, but nobody is well served by unfound­ed claims about the death penal­ty. Nothing is known about how poten­tial mur­der­ers actu­al­ly per­ceive their risk of punishment.”

The report found three fun­da­men­tal flaws with exist­ing stud­ies on deterrence:

• The stud­ies do not fac­tor in the effects of non­cap­i­tal pun­ish­ments that may also be imposed.
• The stud­ies use incom­plete or implau­si­ble mod­els of poten­tial mur­der­ers’ per­cep­tions of and response to the use of capital punishment.
• Estimates of the effect of cap­i­tal pun­ish­ment are based on sta­tis­ti­cal mod­els that make assump­tions that are not credible.

The National Resource Council’s con­clu­sions are sup­port­ed by a num­ber of earlier studies.

Death and Deterrence Redux: Science, Law and Causal Reasoning on Capital Punishment 

In an arti­cle in the Ohio State Journal of Criminal Law, Dr. Jeffrey Fagan of Columbia University describes numer­ous seri­ous errors in recent deter­rence stud­ies, includ­ing improp­er sta­tis­ti­cal analy­ses and miss­ing data and vari­ables that are nec­es­sary to give a full pic­ture of the crim­i­nal jus­tice sys­tem. Fagan writes, ​“There is no reli­able, sci­en­tif­i­cal­ly sound evi­dence that [shows that exe­cu­tions] can exert a deter­rent effect…. These flaws and omis­sions in a body of sci­en­tif­ic evi­dence ren­der it unre­li­able as a basis for law or pol­i­cy that gen­er­ate life-and-death deci­sions. To accept it uncrit­i­cal­ly invites errors that have the most severe human costs.” Since the land­mark Supreme Court deci­sion in Furman v. Georgia in 1972, dozens of stud­ies have been per­formed to deter­mine whether future mur­der­ers are deterred by the death penal­ty. In the past five years, Fagan writes, a ​“new wave” of stud­ies has emerged, claim­ing that each exe­cu­tion pre­vents 3 – 32 mur­ders, depend­ing on the study. Some of these stud­ies tie par­dons, com­mu­ta­tions, exon­er­a­tions, and even irra­tional mur­ders of pas­sion to increas­es in mur­der rates. While many of these stud­ies have appeared in aca­d­e­m­ic jour­nals, they have been giv­en an uncrit­i­cal and favor­able recep­tion in lead­ing news­pa­pers. Fagan takes issue with this lack of seri­ous and ade­quate peer review by fel­low researchers. He ana­lyzed this research and found that ​“this work fails the tests of rig­or­ous repli­ca­tion and robust­ness analy­sis that are the hall­marks of good sci­ence.”(4 Ohio State Journal of Criminal Law 255 (2006))

The Death Penalty: No Evidence for Deterrence

In an arti­cle enti­tled The Death Penalty: No Evidence for Deterrence, John Donnohue and Justin Wolfers exam­ined sta­tis­ti­cal stud­ies that claimed to show a deter­rent effect from the death penal­ty. The authors con­clude that the esti­mates claim­ing that the death penal­ty saves numer­ous lives ​“are sim­ply not cred­i­ble.” In fact, the authors state that using the same data and prop­er method­ol­o­gy could lead to the exact oppo­site con­clu­sion: that is, that the death penal­ty actu­al­ly increas­es the num­ber of mur­ders. The authors state: ​“We show that with the most minor tweak­ing of the [research] instru­ments, one can get esti­mates rang­ing from 429 lives saved per exe­cu­tion to 86 lives lost. These num­bers are out­side the bounds of cred­i­bil­i­ty.” (The Economists’ Voice, April 2006).

The Uses and Abuses of Empirical Evidence in the Death Penalty Debate

In 2005, the Stanford Law Review pub­lished an arti­cle enti­tled Uses and Abuses of Empirical Evidence in the Death Penalty Debate. The arti­cle exam­ines and per­forms com­par­i­son tests on stud­ies that have claimed a deter­rent effect to the death penal­ty. Authors John J. Donohue of Yale Law School and Justin Wolfers of the University of Pennsylvania state their goal and con­clu­sions: ​“Aggregating over all of our esti­mates, it is entire­ly unclear even whether the pre­pon­der­ance of evi­dence sug­gests that the death penal­ty caus­es more or less mur­der.” (58 Stanford Law Review 791 (2005)).

The Death Penalty Meets Social Science: Deterrence and Jury Behavior Under New Scrutiny 

Robert Weisberg, a pro­fes­sor at Stanford University’s School of Law, exam­ined stud­ies on deter­rence and the death penal­ty, as well as oth­er social sci­ence research regard­ing cap­i­tal pun­ish­ment in the U.S. In The Death Penalty Meets Social Science: Deterrence and Jury Behavior Under New Scrutiny, Weisberg notes that many of the new stud­ies claim­ing to find that the death penal­ty deters mur­der have been legit­i­mate­ly crit­i­cized for omit­ting key vari­ables and for not address­ing the poten­tial dis­tort­ing effect of one high-exe­cut­ing state, Texas. Later in the arti­cle, Weisberg exam­ines stud­ies on race-of-vic­tim dis­crim­i­na­tion and on cap­i­tal jurors. This arti­cle will appear in the forth­com­ing edi­tion of the Annual Review of Law and Social Science. (1 Annual Review of Law and Social Science 151 (2005)).

Public Policy Choices on Deterrence and the Death Penalty: A Critical Review of New Evidence

In tes­ti­mo­ny before the Massachusetts Joint Committee on the Judiciary regard­ing pro­posed leg­is­la­tion to ini­ti­ate a ​“fool­proof” death penal­ty, Columbia Law School Professor Jeffrey Fagan ana­lyzed stud­ies that claimed that cap­i­tal pun­ish­ment deters mur­ders. He stat­ed that the stud­ies ​“fall apart under close scruti­ny.” Fagan not­ed that the stud­ies are fraught with tech­ni­cal and con­cep­tu­al errors, includ­ing inap­pro­pri­ate meth­ods of sta­tis­ti­cal analy­sis, fail­ures to con­sid­er all rel­e­vant fac­tors that dri­ve mur­der rates, miss­ing data on key vari­ables in key states, weak to non-exis­tent tests of con­cur­rent effects of incar­cer­a­tion, and oth­er defi­cien­cies. ​“A close read­ing of the new deter­rence stud­ies shows quite clear­ly that they fail to touch this sci­en­tif­ic bar, let alone cross it,” Fagan said as he told mem­bers of the com­mit­tee that the recent deter­rence stud­ies fell well short of the demand­ing stan­dards of social sci­ence research. (J. Fagan, Public Policy Choices on Deterrence and the Death Penalty: A Critical Review of New Evidence, tes­ti­mo­ny before the Joint Committee on the Judiciary of the Massachusetts Legislature on House Bill 3934, July 14, 2005).

New Claims about Executions and General Deterrence: Deja Vu All Over Again?

A study con­duct­ed by Professor Richard Berk of the UCLA Department of Statistics iden­ti­fied sig­nif­i­cant sta­tis­ti­cal prob­lems with the data analy­sis used to sup­port stud­ies claim­ing to show that exe­cu­tions deter crime in the United States. In ​“New Claims about Executions and General Deterrence: Deja Vu All Over Again?,” Professor Berk address­es the prob­lem of ​“influ­ence,” which occurs when a very small and atyp­i­cal frac­tion of the avail­able data dom­i­nates the sta­tis­ti­cal results of a study. He found that this sta­tis­ti­cal prob­lem is found in a num­ber of recent stud­ies claim­ing to show that cap­i­tal pun­ish­ment deters vio­lent crime. The UCLA study con­duct­ed by Berk found that in many instances the num­ber of exe­cu­tions by state and year is the key explana­to­ry vari­able used by researchers, despite the fact that many states in most years exe­cute no one and few states in par­tic­u­lar years exe­cute more than five indi­vid­u­als. These val­ues rep­re­sent about 1% of the avail­able obser­va­tions that could have been used by researchers to draw con­clu­sions for ear­li­er stud­ies claim­ing to find that cap­i­tal pun­ish­ment is a deter­rent. In Professor Berk’s study, a re-analy­sis of the exist­ing data shows that claims of deter­rence are a sta­tis­ti­cal arti­fact of this anom­alous 1%. (Published on UCLA’s Web site, July 19, 2004).