Measuring Innocence: How to Think About the Rate of Wrongful Conviction

What is the rate of wrongful conviction? This question may be implicit in Blackstone’s ratio: “It is better that ten guilty persons escape than that one innocent suffer.” Scholarship designed to provide an empirical answer, however, emerged only with the rise of the “innocence movement” in the United States. This article does not provide another study estimating the rate of wrongful felony conviction either for a specified sample, such as death sentences within a specified time period, or for an entire jurisdiction. Instead, we evaluate the rate question itself and assess its importance to innocence scholarship and action. We first trace the question’s intellectual lineage, and its historical and ideological roots among innocence believers and innocence skeptics. We then describe and evaluate all or most of the published studies attempting to estimate the wrongful conviction rate. Next, we discuss a reoccurring limitation of this published work, namely, its failure to account for or its unsubstantiated assumptions about guilty pleas and misdemeanor convictions among innocent defendants. Finally, we question the continued importance of the rate question in light of the modern innocence movement and its growing accomplishments.