Dr. Jeffrey Fagan, a pro­fes­sor at Columbia University Law School and a lead­ing nation­al expert on deter­rence, tes­tifed that recent stud­ies claim­ing to show a deter­rent effect to cap­i­tal pun­ish­ment are fraught with tech­ni­cal and con­cep­tu­al errors. Fagan not­ed that a string of recent stud­ies pur­port­ing to show that the death penal­ty can pre­vent mur­ders use inap­pro­pri­ate meth­ods of sta­tis­ti­cal analy­sis, fail to con­sid­er all the rel­e­vant fac­tors that dri­ve mur­der rates, and do not con­sid­er impor­tant vari­ables in key states. During his tes­ti­mo­ny before com­mit­tees of the New York Assembly gath­er­ing infor­ma­tion regard­ing the future of the state’s statute, Dr. Fagan stat­ed:

These stud­ies fail to reach the demand­ing stan­dards of social sci­ence to make such strong claims, stan­dards such as repli­ca­tion and basic com­par­isons with oth­er sce­nar­ios. Some sim­ple exam­ples and con­trasts, includ­ing a care­ful analy­sis of the expe­ri­ence in New York State com­pared to oth­ers, lead to a rejec­tion of the idea that either death sen­tences or exe­cu­tions deter mur­der.… A close read­ing of the new deter­rence stud­ies shows quite clear­ly that they fail to touch this sci­en­tif­ic bar, let alone cross it.

For a full dis­cus­sion of the prob­lems iden­ti­fied by Dr. Fagan, read the text of his tes­ti­mo­ny in PDF for­mat. (“Deterrence and the Death Penalty: A Critical Review of New Evidence,” Dr. Jeffrey Fagan, January 21, 2005). See also, Deterrence.

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