A second controversy involves social, not medical, science. Justice Breyer, joined by Justice Ginsburg), wanted the Court to ask for "full briefing on ... whether the death penalty violates the Constitution." He maintained that "the death penalty, in and of itself, now likely constitutes a legally prohibited 'cruel and unusual punishmen[t].'" One aspect of this tentative conclusion involved "the death penalty's deterrent effect" -- the subject of innumerable studies and two skeptical reports from the National Academy of Sciences.
Justice Scalia, joined by Justice Thomas, was upset at what he called the "speculat[ion] that it does not 'seem likely' that the death penalty has a 'significant' deterrent effect." His approach to this empirical question was quintessentially legal, not scientific -- pick the answer you want (or think you know) and look only for confirming evidence. Justice Scalia's argument that the existence of the death penalty (even if rarely used and long delayed) deters significantly more than life imprisonment does consists of a single sentence: "It seems very likely to me, and there are statistical studies that say so." What studies?
Justice Scalia would have done better to have followed the example of Andrew Lang, the novelist who tried "not to use statistics as a drunken man uses lamp-posts, for support rather than for illumination." 1/ Carelessly or cavalierly, Justice "Scalia cites a paper by Cass Sunstein for a second time, even though after the first such Scalia citation in an earlier lethal injection case, Cass Sunstein (writing with Justin Wolfers) affirmed his view that there is no credible evidence that the death penalty is a deterrent." 2/ As Professor John Donahue, who penned these words, added, "[o]ne would hope for more from a Supreme Court justice than citations to junk science and to a paper withdrawn based on more informed consideration – especially on a matter of life and death." 3/
- On the origin of this aphorism, see Quote Investigator, Jan. 14, 2015, http://quoteinvestigator.com/2014/01/15/stats-drunk/.
- John J. Donohue, Glossip v. Gross: Examining Death Penalty Data for Clarity, Stanford Lawyer, June 29, 2015, https://stanfordlawyer.law.stanford.edu/2015/06/glossip-v-gross-examining-death-penalty-data-for-clarity/. Justice Breyer is both less dogmatic and more complete in his description of the body of social science research:
Many studies have examined the death penalty's deterrent effect; some have found such an effect, whereas others have found a lack of evidence that it deters crime. [Citations omitted.] Recently, the National Research Council ... reviewed 30 years of empirical evidence and concluded that it was insufficient to establish a deterrent effect and thus should "not be used to inform" discussion about the deterrent value of the death penalty. National Research Council, Deterrence and the Death Penalty 2 (D. Nagin & J. Pepper eds. 2012).
I recognize that a 'lack of evidence' for a proposition does not prove the contrary. [Citation omitted.] But suppose that we add to these studies the fact that, today, very few of those sentenced to death are actually executed, and that even those executions occur, on average, after nearly two decades on death row. ... Then, does it still seem likely that the death penalty has a significant deterrent effect?