The article says, regarding the opinions in Baze v. Rees, "Justice Antonin Scalia cited a suggestion by Sunstein (with co-author Adrian Vermeule) that 'a significant body of recent evidence' shows 'that capital punishment may well have a deterrent effect, possibly a quite powerful one.'" Here is the actual passage:

Justice Stevens' analysis barely acknowledges the “significant body of recent evidence that capital punishment may well have a deterrent effect, possibly a quite powerful one.” Sunstein & Vermeule, Is Capital Punishment Morally Required? Acts, Omissions, and Life-Life Tradeoffs, 58 Stan. L. Rev. 703, 706 (2006); see also id., at 706, n. 9 (listing the approximately half a dozen studies supporting this conclusion). According to a “leading national study,” “each execution prevents some eighteen murders, on average.” Id., at 706. “If the current evidence is even roughly correct . . . then a refusal to impose capital punishment will effectively condemn numerous innocent people to death.” Ibid.

The Sunstein and Vermeule article is a philosophical essay, not empirical research. It is cited as a convenient collection and summary of the research, just as one might cite a student note in a law review for its collection of authoritative cases on a subject. The authority is the underlying research, not the Sunstein and Vermeule article. The fact that those two authors hedged on whether deterrence has been shown therefore means very little. They are, after all, law professors and not empirical researchers.

The op-ed states, on the basis of no authority other than the non-peer-reviewed Donohue and Wolfers article, that " the best reading of the accumulated data is that they do not establish a deterrent effect of the death penalty." If by "establish" they mean conclusively prove, then that is true but misleading. Nearly every reputable scholar in this debate agrees that the case has not been conclusively proved either way, and it may never be. The evidence is very strong, however, that the death penalty does have a deterrent effect and does save innocent lives when it is actually enforced. As Professor Paul Rubin testified to Congress, "The literature [on deterrence] is easy to summarize: almost all modern studies and all the refereed studies find a significant deterrent effect of capital punishment."

That is what Justice Scalia cited the research for, and it is not a misreading at all. It is correct.