American Evidence law expert D. Michael Risinger defined “wrongful conviction” in three ways: “The term “wrongful conviction” simply cannot be comfortably avoided, but it must always be approached with caution, because it can easily lead to the conflation of three importantly different problems of justice. The first is the problem of convicting those who are factually innocent either bcause no crime was committed or, more commonly, because a crime was in fact committed, but by someone else (wrongful conviction in the factual sense).
The second is the problem of convicting a person who has undoubtedly performed the actus reus of a crime for which they are not culpable, either because of insanity or the absence of some other required indicium of culpability, usually a particular required mental state (wrongful conviction in the culpability sense).
The third is the conviction of persons who may very well be both factually guilty and culpable, but who were convicted in trials containing procedural errors not easily dismissed..”
Crime scholars doubt that governments will ever collect wrongful convictions statistics because (1) the operational definition of a wrongful conviction is highly problematic and contestable in many cases; (2) data gathering, storage, and usage is expensive; (3) institutions gather statistics for practical reasons based on perceived institutional needs; and (4) like gathering crimes-known-to-the-police data in America, criminal justice data collection is unusually tedious because of the hyper-fragmentation of criminal justice agencies in the United States. At present, the idea of wrongful convictions is too challenging to the legitimacy of criminal justice, and the practical problems are too daunting, for general data collection by the federal or state governments to be minimally plausible.
Gross and O’Brien add, more fundamentally, that miscarriages of justice are invisible when they occur, so it is not possible to relate the “accident” to a contemporary context of similar cases. When the wrong is discovered, years later, it is often by chance. Even today, with innocence projects reviewing prisoners’ petitions, there are so many petitions for assistance and the selection standards are so high, that some actually innocent prisoners will be lost in the triage.
The possibility of getting a valid numerator for more run-of-the-mill felonies than death sentence cases is close to impossible at present. When an exoneration does occur years later, the records of other similar or matched cases are impossible to retrieve. Given the highly decentralized American justice system and the lack of retrievable case data in all but a tiny fraction of cases, the denominator is also impossible to construct.
As a result, analysts like Robert Schehr, who have assumed that wrongful conviction estimates should be precise figures based on “counted” miscarriages of justice, are correct in concluding that such a “Uniform Miscarriage Reports,” if you will, are not possible. Were such data available they could be used to compare the relative accuracy of different agencies, but such a vision is utopian as the data for making precise quantitative estimates of wrongful conviction are not available.
This does not mean that a qualitative estimate is without use. The purpose of a qualitative and plausible Estimate is to confirm the reality that wrongful convictions occur with regularity across the nation (but perhaps not in specific agencies or locales) and to provide a meaningful figure (even without the “precision” of a crime rate) that would justify innocence reforms. A plausible Estimate, grounded in available and accurate information, is also a useful counter to unfounded arguments of conservative critics. The conventional, layperson’s view focuses on wrongful convictions only in the factual sense, and perhaps the culpability sense as well. It is worth considering, however, that the adversary process has developed theories and practices over centuries with the sophisticated understanding that ascertaining the truth of an event can be a devilishly difficult business. Adversary system dogma holds that reliance on procedures such as public adversary trials and standards like proof beyond a reasonable doubt will generate fewer errors than other modes of trial.
Source : Criminal Law Bulletin, Volume 48, Number 2, Qualitatively Estimating the Incidence of Wrongful Convictions by Marvin Zalman.