The Blackstone Ratio at the Supreme Court

My colleague David Feige makes the following observation about the role of the Blackstone Ratio in our criminal justice system:

[In Kansas v. Marsh, Scalia] concluded that “The rate at which innocent people are convicted of felonies is less than three-hundredths of 1 percent – .027 percent, to be exact”. Scalia sleeps well knowing our system works so brilliantly. The problem, of course is that .027 percent is a hoax, and . . . I [am] struck once again that a justice generally considered to be so bright could get something this important so fundamentally wrong. But one need only look at the study Scalia cites (by Joshua Marquis, a stalwart of the prosecutorial lobby) to understand the error of his ways.

Marquis came up with the number that Scalia adopted much like a toddler solving a problem in a kindergarten math workbook: He took the total number of exonerations, (north of 200 now) picked a gratuitous multiplier (10 purely for rhetorical purposes), and then divided by 15 million—the total number of convictions during the period of years he considered. . . . As I’ve previously pointed out, here’s why that’s a ludicrous methodology.

So how should one “do the math?” Another colleague of mine, Michael Risinger, was recently cited in Justice Stevens’ concurrence in Baze v. Rees for his work on the issue.

Risinger explains his methodology (and applies it) in this piece. He states:

If one is at all serious about trying to determine the empirical truth about the magnitude of the wrongful conviction problem, one must make an attempt to associate the denominator with the same kind of cases represented in the numerator. . . . I have tried to do just that. Using only DNA exonerations for capital rape-murders from 1982 through 1989 as a numerator, and a 407-member sample of the 2235 capital sentences imposed during this period, this article shows that 21.45%, or around 479 of those, were cases of capital rape murder. Data supplied by the Innocence Project of Cardozo Law School and newly developed for this article show that only two-thirds of those cases would be expected to yield usable DNA for analysis. Combining these figures and dividing the numerator by the resulting denominator, a minimum factually wrongful conviction rate for capital rape-murder in the 1980’s emerges: 3.3%.

As Justice Stevens has stated, “Abundant evidence accumulated in recent years has resulted in the exoneration of an unacceptable number of defendants found guilty of capital offenses.”