Innocents Convicted: An Empirically Justified Wrongful Conviction Rate

Abstract:     
That would make the error rate [in felony convictions] .027 percent - or to put it another way, a success rate of 99.973 percent.

- Justice Antonin Scalia, concurring in Kansas v. Marsh, June 29, 2006 (quoting Joshua Marquis)

The news about the astounding accuracy of felony convictions in the United States, delivered by Justice Scalia and Joshua Marquis in the passage set out epigrammatically above, would be cause for rejoicing if it were true. Imagine. Only 27 factually wrong felony convictions out of every 100,000! Unfortunately, it is not true, as the empirical data analyzed in this article demonstrates.

To a great extent, those who believe that our criminal justice system rarely convicts the factually innocent and those who believe such miscarriages are rife have generally talked past each other for want of any empirically-justified factual innocence wrongful conviction rate. This article remedies at least a part of this problem by establishing the first such empirically justified wrongful conviction rate ever for a significant universe of real world serious crimes: capital rape-murders in the 1980's.

Using DNA exonerations for capital rape-murders from 1982 through 1989 as a numerator, and a 406-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 67% 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%.

The article goes on to consider the likely ceiling accompanying this 3.3% floor, arriving at a slightly softer number for the maximum factual error rate of around 5%. The article then goes on to analyze the implications of a factual error rate of 3.3%-5% for both those who currently claim errors are extremely rare, and those who claim they are extremely common. Extension of the 3.3%-5% to other capital and non-capital categories of crime is discussed, and standards of moral duty to support system reform in the light of such error rates is considered at length.

Keywords: Criminal Law, Criminal Procedure, Wrongful Convictions, Evidence, Proof, Standard of Proof, Empirical Wrongful Conviction Rate, Actual Innocence, Unsafe Verdict

JEL Classifications: K14, K41

Working Paper Series