Measuring Wrongful Convictions Research Paper

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Measuring wrongful convictions includes counting exonerations, estimating the incidence of wrongful convictions, and measuring the correlates of wrongful convictions in known exoneration cases. Measuring wrongful convictions is an important task because it can be used to evaluate the inaccuracy and unfairness of the criminal justice system.

A wrongful conviction is a conviction that is factually inaccurate, that is, the wrong person was convicted or a person was convicted for a crime that did not occur. An actual innocence exoneration is an official act that erases the legal status of guilt based on a judgment of factual innocence.

Wrongful convictions are inherently difficult to establish because they are “invisible” when they occur, the process of reconstructing equivocal evidence that led to a conviction in the first place is difficult, and prosecutors and courts are resistant to opening old convictions.

Lists of exonerations are not kept by government agencies but by private organizations like the Innocence Project and the National Registry of Exonerations.

Quantitative studies of wrongful death penalty convictions estimate that about three in 100 defendants sentenced to die are factually innocent. Qualitative estimates of wrongful convictions among all felonies, based on descriptions of the quality of criminal justice and other factors, plausibly conclude that at least 1 % of all felony convictions are factually inaccurate.

Studies of exoneration cases show that such factors as eyewitness misidentification, police tunnel vision, false confessions, informants’ deception, erroneous forensic evidence, and misconduct and incompetence by prosecutors and defense attorneys occur in wrongful conviction cases in significant quantities.


This research paper discusses the measurement of wrongful convictions occurring in the United States. Two types of measurement are discussed: (1) the number and rates of factually wrongful convictions and (2) measures of the factors (correlates) discovered in such cases. Measuring the number of wrongful convictions is divided into counting wrongful convictions and estimating their rates.

Inaccurate convictions are indicative of an improperly functioning criminal justice system. Convicting factually innocent people means that the process is not effective or efficient. More important, convicting the innocent is an injustice that every legal system wishes to avoid. Knowing something about such cases, including their overall numbers and correlates, is necessary to decide whether the problem requires a policy response and, if so, how to respond.

It should be noted that “false acquittals,” when juries acquit defendants who in fact committed criminal acts with the requisite criminal intent, are also injustices. As both kinds of errors of justice may stem from operational flaws and informational deficiencies in the criminal justice process, research on measuring and correcting wrongful convictions should help reduce wrongful acquittals. Although a large number of factually guilty people are never convicted of crimes, such “errors of impunity” mostly result from crimes never being discovered or reported in the first place and other deficiencies of police agencies (Forst 2004). Such injustice is not usually related to the kinds of justice system processing errors that lead to wrongful convictions or acquittals.

The terms prevalence and incidence, used in medicine and epidemiology, which are sometimes confused, have been used to describe rates of wrongful convictions. Prevalence is an epidemiological measure of the existence of a disease or condition in a population and is calculated by dividing the number of persons with a disease or condition at a particular time by the number of individuals examined. Incidence measures the rate of occurrence of new cases and is calculated as the number of new cases of a disease or condition in a specified time period (usually a year) divided by the size of the population under consideration who are initially disease free. Both measures can be expressed as rates (Crichton 2000). It makes some sense to measure the prevalence of wrongfully convicted prisoners, but the more useful measure of wrongful conviction rates for the purpose of assessing the criminal justice process is the incidence that occurs in a year.

Defining And Measuring Wrongful Convictions

To measure a social category, it must be defined. Wrongful conviction can mean different things. A conviction can be wrong and reversed on appeal because it was obtained on the basis of a serious violation of the defendant’s procedural or constitutional rights. Such a conviction is wrongful in the procedural or legal sense. A conviction can also be wrong because a jury was mistaken about a defendant’s culpability, as, for example, regarding a self-defense claim. In this research paper, a wrongful conviction means actual or factual innocence. This occurs when a crime was committed and the person convicted had nothing to do with it (i.e., the “wrong person” scenario, where a jury erroneously discounted an alibi), or no crime was committed, but a court imputed criminal liability (Risinger 2007). The latter situation has occurred in cases involving fire-related deaths and the deaths of infants, where guilt was wrongfully based, respectively, on erroneous technical or medical evidence about arson or shaken baby syndrome. The term false conviction is a synonym for convictions that are wrongful in the factual sense. Scholars agree that false convictions should be included in measurements of factual innocence. There is some uncertainty about whether cases that are wrongful in the culpability sense should be included in the measurement of wrongful convictions.

A measurable entity “must be identifiable by some means and identified by us. And we must know something about its properties and behavior, so that we can relate these to our measures of it” (Gorard 2010:390). This insight raises the question of what exactly is meant by a “conviction,” as a wrongful conviction presupposes a conviction. A conviction is an official decision that is formally entered in the record of a politically legitimate entity following a process of investigation, prosecution, and adjudication. The process leading to a conviction involves many actors and subprocesses and can be brief and routinized or very complex. A conviction, therefore, is a socially constructed artifact. As a result, a wrongful conviction simply does not “exist” but is itself a socially constructed artifact that comes at the end of a process of deconstructing a prior conviction. The process of deconstruction can be done by a private entity (e.g., journalist, legal scholar, social scientist, or research group), resulting in an unofficial judgment of a false conviction. The process can also be accomplished by an official body, resulting in an official exoneration. Understanding the process by which a conviction (and therefore a wrongful conviction) is produced allows researchers to not only count them but also to measure the factors present that may logically have led to the erroneous verdict.

The definition of a false conviction raises several difficulties. The inherent limitations of proof in the absence of incontrovertible evidence have led to the standard of conviction “beyond a reasonable doubt.” This means that a conviction might be false and that, concomitantly, an acquittal might also be false. Lingering uncertainty about the relationship between legal and factual guilt or innocence provides an initial basis for exploring whether some convictions are false, especially when nonDNA exonerations are compared to DNA exonerations. To avoid this difficulty, some enumerations of wrongful convictions or exonerations either apply or claim to apply “objective” standards. However, in some cases (e.g., an acquittal in a retrial of a case after a successful appeal), the “objective” legal acquittal can raise the same lingering uncertainty as an initial acquittal regarding factual innocence. This suggests that some level of judgment about case facts (similar to the judgment leading to a conviction, but not similar to the process of jury deliberation) is necessary to generate a conclusion that a conviction was false and that the exoneree is factually innocent.

Another issue is that some person or institution must define whether a conviction was wrongful. The standard applied by the particular writer or research group, or by a governmental body, must be examined to determine how it defines a wrongful conviction; the goals and organizational imperatives of the decision-making person or body should also be considered. This will be considered below in the section on “Counting Wrongful Convictions.”

A clear distinction must be drawn between exonerations and wrongful convictions. In common usage, the terms are sometimes employed interchangeably. An exoneration is an official act by a judge or governmental officer that erases the legal status of guilt previously imposed on a person. Researchers listed four kinds of exonerations: pardons issued by governors or other executive officers based on evidence of innocence; cases dismissed by courts after new evidence of innocence, like DNA, is presented; acquittals in retrials, but only if the basis is evidence that the defendant had no role in the crime; and a few cases where states posthumously acknowledged the innocence of defendants who had died in prison (Gross et al. 2005). This definition of exonerations includes both objective and subjective or judgmental elements. Exonerations may also be issued by official bodies with jurisdiction to determine the amounts of compensation for wrongful convictions or to declare a status of innocence (discussed below).

Official exonerations are a subset of a larger number of cases identified as wrongful convictions by authors, research scholars, and private organizations, often as a result of exhaustive research. Unless an official body declares that a conviction was wrongful, and as a matter of law erases the conviction, the wrongful conviction cannot properly or legally be called an exoneration. This is so even if the judgment that a false conviction occurred is based on ample and powerful supporting evidence. Indeed, prosecutors in some cases in which a prisoner won an appeal and is facing retrial will offer to dismiss the case if the prisoner, facing the risk of reconviction, pleads guilty to a lesser crime and is released for time served. This allows prosecutors to claim that the prisoner was actually guilty in the face of contrary evidence, thereby saving face and avoiding a lawsuit against police and prosecutors. Such action depresses and distorts the number of justifiable exonerations.

A more controversial point, addressed in the section on “Estimating Wrongful Convictions,” is that known exonerations and wrongful convictions are a minor subset of all wrongful convictions. This is plausible, considering that social measurements, including the United States census and official crime data, tend to undercount the phenomenon being measured (Loftin and McDowall 2010).

The Inherent Difficulty Of Measuring Wrongful Conviction

Whether data about wrongful convictions are collected by researchers or potentially by government agencies, the task is inherently difficult. In most jurisdictions, there is no routine legal mechanism to review prior convictions for the possibility that they were factually erroneous, although this is beginning to change (discussed below). Moreover, a wrongful conviction is invisible when it occurs. Miscarriages of justice are typically uncovered years after they occur and only after arduous investigations on behalf of prisoners by friends and relatives or by innocence projects. They are often discovered by chance, as when a forensic analyst happens to save biological evidence samples (when to do so is not standard procedure), which later provide exonerating DNA profiles. As a result, although lists of wrongful convictions have been collected by several organizations, it is not possible to relate them to the context of similar cases that occurred at the same time. This makes it close to impossible to directly measure the incidence of wrongful convictions (Gross and O’Brien 2008).

Another difficulty in establishing that a conviction was false is that many cases have equivocal evidence, and determining whether the conviction was accurate in the first place requires an element of judgment. As a result, convictions that are deemed false by many will be disputed by others. Additionally, the limited resources of innocence projects and their high standards in accepting cases, other attendant costs of seeking exonerations, and the general reluctance or opposition of government agencies to open closed cases inevitably mean that many wrongful convictions will never be uncovered.

Innocence scholars and critics generally agree that it is impossible to precisely measure the incidence of false convictions (Schehr 2005). This understanding has led some to opine that the number of such miscarriages of justice is minuscule (Marquis 2006; Hoffman 2007). No writer now suggests that wrongful convictions never occur, acknowledging at least the accuracy of the Innocence Project’s list of DNA exonerations (Innocence Project n.d.). Analysts who closely study wrongful convictions, however, assert with confidence that the small number of known DNA and non-DNA exonerations are indicative of much larger numbers of false convictions (Gross et al. 2005; Garrett 2011).

Government Institutions That Establish Actual Innocence

The traditional methods of establishing official exonerations – pardon, judicial dismissal, and acquittal after a reversal – are ambiguous. These methods may exonerate former and current prisoners for legal or humanitarian reasons, rather than on account of factual innocence. Even if raw counts of such decisions were kept, the records that underlie the decisions would have to be inspected to determine if the ground was actual innocence. In addition to these modalities, courts and agencies given the authority to grant state compensation for wrongful convictions have the potential to keep and publish records of false convictions. The federal government has had a compensation law since 1938, and awards are made by the United States Court of Federal Claims. In recent years, the number of states that authorize compensation for wrongful conviction has grown to twenty-seven (Norris 2011).

Nevertheless, some recent compensation statutes set very high standards of proof and include numerous disqualifications that may deny compensation and, by implication, a finding of innocence to claimants with justifiable wrongful conviction cases (Norris 2011). For example, James Richardson had been exonerated by Florida for murder in 1989 in a special proceeding in which Janet Reno, later Attorney General of the United States, was appointed a special prosecutor. She moved to dismiss his prosecution on a nolle prosse in a memorandum which concluded that he was “probably wrongfully accused.” When Florida enacted the Victims of Wrongful Incarceration Compensation Act in 2009, Richardson petitioned for compensation, but was denied because the nolle prosse did not establish by clear and convincing evidence that he was actually innocent. The anomalous situation of one state institution exonerating a person and another institution of the same state not exonerating the person for the same crime can play havoc with clarity in determining the existence of exonerations and wrongful convictions (Zalman 2012).

Several states have, by statute, authorized courts or other agents to declare convicted persons actually innocent. In 2001, Virginia authorized its Supreme Court to issue writs of actual innocence based on biological evidence and in 2004 authorized the issuance of such writs on the basis of nonbiological evidence. North Carolina established an Innocence Inquiry Commission in 2006 to investigate petitions by prisoners and where it finds sufficient evidence of actual innocence to refer such cases to a superior court for a three-judge trial to determine actual innocence. In 2008, Illinois authorized circuit courts to issue certificates of innocence to petitioners who can prove their innocence on a preponderance of the evidence. In that year, Utah also established a procedure allowing district courts to find a person factually innocent. Several states, including Illinois and Texas, now have provisions for governors or pardon boards to issue pardons based on innocence.

Courts typically do not keep accessible records that are useful to the public or the research community, and records of findings of actual innocence will be no different. Innocence issues, however, are now visible to such organizations as the National Registry of Exonerations (n.d.) and Justice Denied (n.d.), making it more likely that exonerations announced under new state compensation laws and declaration-of-innocence procedures by court and pardon boards will be tracked and listed.

Counting Wrongful Convictions

No government agency or court maintains an accessible list of exonerations, although several have the authority to issue exonerations. Most information on wrongful convictions, including counts, has been produced by journalists, writers, researchers, and organizations.

Big Picture Books. Beginning with Borchard’s 1932 book, Convicting the Innocent, a number of “big picture books” (Leo 2005) detailed cases of exonerations, describing the factors that appeared to be sources of the miscarriages of justice. Borchard listed 65 cases, most of which had occurred within a decade or two of the book’s publication. Although he was a law professor, Borchard wrote a journalistic book designed to arouse popular concern. His goal was to firmly establish that wrongful convictions can and do occur. He used the book to successfully lobby for the passage of a federal compensation law for exonerees. His list of 65 exonerations (most were American, a few were English) was the first such compilation. The number grew as other similar books have been published since the 1950s (Frank and Frank 1957; Yant 1991). In addition, scores of books, typically written for a popular audience, have been written about single wrongful conviction cases. They provide a wealth of detailed information about wrongful convictions but typically do not relate the information to a growing body of wrongful conviction scholarship (Leo 2005).

Scheck et al. (2000), a popular and influential book describing DNA exonerations obtained by the Innocence Project in the 1990s, focused on factors related to wrongful convictions. An appendix provides data on 74 false convictions, including jurisdiction, twelve causal factors, length of maximum sentence, time served before exoneration, the number of mistaken witnesses per case, and the race of the crime victims and the exonerated defendants.

Scholarly Lists and Evaluations. Rattner (1988) analyzed 205 “old and new legal cases” of wrongful conviction occurring in the United States after 1900 “derived from books, documents, and newspaper clippings.” Most of the cases had been previously described in big picture books, supplemented with more recent news reports. Most resulted in legal exonerations (three were paroled, and data was missing for 15). In 40.5 % of the cases, the real culprit was apprehended. The violent crimes of murder, robbery, and rape accounted for 87 % of the convictions. Rattner described the distribution of sentences (45.8 % of the known sentences were death or life in prison) and the types of error associated with the wrongful convictions (52 % of the cases with known or listed errors included eyewitness identification error).

Gross (1987) assembled 136 cases of misidentification that led to criminal prosecution in the twentieth century. The cases were divided between those occurring before and after the Supreme Court’s lineup decision (U.S. v. Wade 1967). The pre-Wade cases were accounts of convictions derived from the big picture books, while the post-Wade cases were derived from news accounts. Thirty-nine cases, mostly from the post-Wade set, did not result in convictions. Gross used the cases to describe the processes of misidentification and exoneration and to describe historical trends in case processing.

Bedau and Radelet (1987) enumerated 350 capital or potentially capital murder or rape convictions imposed in the twentieth century believed to have been factually erroneous. The list was based on evaluations of the case facts in which the scholars exercised their judgment to conclude that either no crime occurred or the defendant was legally and physically uninvolved in the crime. The article listed the jurisdiction, date, crime of conviction and type of sentence, the primary evidence for the judgment that the conviction was false, and the factors associated with the erroneous convictions.

Gross et al. (2005) scoured many sources to identify 340 official exonerations occurring in the DNA era – for the years 1989–2003. More than half, 57.6 %, were non-DNA exonerations. The vast majority were convicted by trial rather than by plea, and all but 14 cases were convictions for murder or rape. The authors suggested that the fortuitous nature of exoneration must have excluded many robbery cases based on faulty eyewitness identification. They excluded two and possibly three “mass exoneration” cases in which corrupt police planted evidence on innocent people, followed, after discovery, by the exoneration of masses of such people. They also excluded from the exoneration count pending cases, pleas of guilty or no contest where evidence of innocence was strong, inexplicable failures to exonerate people who were patently innocent, and people falsely convicted in the child care sex abuse and satanic ritual cases that swept through America in the 1980s and 1990s.

Organizational Lists. The Death Penalty Information Center (n.d.) (DPIC) maintains an on-line list of exonerated death row inmates since the reinstatement of capital punishment in 1976. The number was 142 as of March 2013. The list includes name, state of conviction, race, year convicted and exonerated, number of years served, the reason for exoneration, and whether it was a DNA exoneration. The DPIC applies an objective standard of legal innocence, which means that a few of the exonerees may have been factually guilty, although wrongful conviction scholarship has established the actual innocence of many.

The Innocence Project (n.d.), affiliated with the Benjamin Cardozo Law School of Yeshiva University, is a self-described “national litigation and public policy organization dedicated to exonerating wrongfully convicted individuals through DNA testing and reforming the criminal justice system to prevent future injustice.” It lists the number of DNA exonerations that have been obtained in the United States since 1989 on its website home page. As of March 2013, the number stood at 303. An accessible list includes each exoneree, the state and years of conviction and release, and a link to a page of more detailed information, including whether the real perpetrator was found, contributing causes, and whether compensation was awarded. This list is frequently cited and is so prominent that some conflate the number of DNA exonerations with the total number of exonerations. This may result from the fact that until recently there has been no other prominent and easily referenced source of total exonerations. Furthermore, DNA exonerations are viewed as virtually incontrovertible, while non-DNA exonerations can be subject to some levels of doubt.

The National Registry of Exonerations (n.d.) (NRE), launched in the spring of 2012, is a joint product of the University of Michigan Law School and the Center on Wrongful Convictions (CWC) at the Bluhm Legal Clinic of Northwestern University School of Law. Its exoneration list, numbering more than 1,060 in early 2013, was drawn from raw lists kept by CWC, the data collected by Gross et al. (2005), the Innocence Project (n.d.), and other sources. It relies on the methodology pioneered by Gross et al. (2005). Each case is reviewed by staff to meet the criteria for exonerations based on actual innocence. For each exoneree, data include county and state of conviction; federal jurisdictions; most serious crime; additional conviction; year of crime; conviction and exoneration; exoneree’s sentence, race, sex, and age at conviction; whether DNA exoneration or not; and contributing factors: mistaken eyewitness identification, false confession, perjury or false accusation, false or misleading forensic evidence, official misconduct, and inadequate legal defense. Clicking on the exoneree’s name displays a few pages listing relevant data items and providing a narrative account of the case. Some narratives are by named authors. (n.d.) maintains a searchable database of the wrongly convicted that as of early 2012 included 3,310 exonerated people from 98 countries. The list can be searched by last name of the party or by location. Searching by location allows a search by American state and federal cases. Each name links to a page that lists years imprisoned, the charge, sentence, year convicted and cleared, location of trial, result, and case summary. Each page provides such sources of information as news articles and legal cases with citations and/or links and books. The listed cases are legal exonerations that include miscarriages of justice that cannot always be classified as cases of factual innocence. is closely related to Justice Denied (n.d.), a volunteer group that publishes Justice Denied magazine in paper and on-line, which “publicizes cases of wrongful conviction, and exposes how and why they occur.”

These lists provide a wealth of raw information about miscarriages of justice. The Innocence Project list is widely cited because it provides a “gold standard” of DNA cases that establish wrongful convictions with little doubt of error. The DPIC list focuses exclusively on death sentence exonerations and is often consulted given the prominence of the death penalty issue. The NRE has the potential of becoming the authoritative source for known DNA and non-DNA exonerations in the United States. The Justice Denied list is accessible and useful for gaining a quick overview of the scope of the numbers of wrongful convictions in the United States and other countries. None of the on-line lists are in formats that allow for quantitative analysis by researchers, although they are useful starting points for scholars wishing to explore the cases more systematically.

Estimating Wrongful Convictions

The fortuitous nature of obtaining exonerations means that counting and cataloging them can never amount to a “census” of all exoneration, let alone of all wrongful convictions that occur in a year. As a result, the incidence of wrongful convictions can only be estimated. In the alternative to estimating, many writers simply assume that the number of wrongful convictions is large enough to constitute a policy issue. Two kinds of estimates have been generated: precise quantitative estimates and qualitative estimates.

Precise Estimates. Poveda (2001) estimated a wrongful conviction rate of 1.4 % for released New York inmates convicted of murder based on (1) an official 1989 New York state study establishing that 21.2 % of inmates committed for murder were granted new trials, (2) the fact that 21.2 % of murder inmates whose cases were discharged by new trials in 1995 were discharged for substantial error, and (3) the assumption that these discharges, constituting 1.4 % of all murder commitments to New York prisons in 1992, were actually innocent.

Risinger (2007) established a wrongful conviction rate for rape-murder death sentences based on eleven DNA exonerations for rapemurder convictions occurring between 1982 and 1989. The numerator was set at 10.5 to produce a conservative estimate. The denominator of 319 was determined by finding (and listing) those individuals sentenced to death for rape-murders in the same time frame when the exonerees were convicted, discounted by the rate of similar cases where no usable DNA was available. This resulted in a wrongful conviction rate of 3.3 % (or 2 % before discounting the denominator for cases in the same period for which no usable DNA was available). Risinger also speculated that in some rape-murder cases the facts of guilt were so clear that DNA testing was not requested, which would further deflate the denominator of rape-murder death sentences consistent with the 11 (or 10½) exonerees, possibly yielding a maximum exoneration rate for this crime of 5 %. Risinger asserted the highly plausible conjecture that rates of wrongful convictions are unevenly distributed.

Gross and O’Brien (2008) examined 2,394 death sentences pronounced in US courts from 1973 to 1984. By 2004, the process of identifying exonerations for these cases had run their course. Fifty-four had been exonerated – a rate of 2.3 %. They then calculated the exoneration rate as of 2004 for those sentenced to death through 1989, again finding a rate of 2.3 % (86/3792). They then assessed the relation between capital exoneration and wrongful conviction rates among those sentences to death. Some capital defendants who were innocent may not have been exonerated because they did not participate in the arduous exoneration process or because they were executed, died from other causes, or had their sentences commuted to life terms (which reduces the pressure on innocence projects or others to seek their exoneration). It is possible that some among the exonerated participated in the murders for which they were convicted. Nevertheless, Gross and O’Brien estimate that the probability of innocence is very high for capital exonerees and the number of misclassifications low enough for the capital exoneration figure (2.3 %) to stand as a proxy for false death sentences of the actually innocent.

Roman et al. (2012) examined an unbiased cohort of 634 Virginia post-conviction sexual assault and/or homicide cases with DNA evidence resulting in 715 convictions, dating from 1973 to 1987. In 5.3 % of the cases, the offender was eliminated as a source of DNA, and the DNA exclusion was accompanied with probative evidence that appeared to support exoneration. In another 2.5 % of the cases, the offender was eliminated as a source of DNA, but the exclusion was not accompanied with probative exoneration evidence. This is the strongest empirical evidence to date that establishes the existence of a substantial proportion of wrongful convictions in a sample of general cases, rather than in group of cases that were targeted because they appeared to be miscarriages of justice.

General Estimates. Death sentence data tracked by the government and private groups are unusual in providing precise numbers of capital sentences, exonerations, and other case disposition information. This allows precise estimates of exonerations and wrongful convictions for this tiny fraction of the approximately one million felony convictions handed down by courts annually. The lack of precise or easily accessible data from court records makes it impossible to estimate wrongful felony conviction levels in the way that has been accomplished with capital sentences. In the absence of any general estimate, many wrongful conviction writings, especially by legal scholars, simply assume that the number is sufficiently large to constitute a problem needing to be addressed.

Huff et al. (1986) surveyed the opinions of state attorneys general and Ohio justice officials and defense lawyers about the annual incidence of wrongful conviction. Their estimates in the mid-1980s ranged from never (5.6 % of respondents) to less than 1 % (71.8 %), to 1–5 % (20.3 %), and to 6–10 % (2.3 %). The authors suggested that if an overall estimate of 0.5 % was accurate, it would mean more than 5,000 wrongful convictions occur each year. Observers have noted that these estimates are essentially guesses. Huff et al., however, did not assert that these estimates are a precise measure of wrongful convictions, but rather that the broader sampling of expert opinion provided some boundaries for the authors’ own estimate of wrongful conviction incidence.

Ramsey and Frank (2007) updated and replicated Huff et al. (1986) with a sample of Ohio justice officials and defense lawyers reporting their beliefs about the frequency of wrongful convictions. Their modal response, taken as a whole, was that such error occurred in less than 0.5 % of cases in their own jurisdiction and in 1–3 % of cases in the United States. Defense attorneys reported higher estimates and police and prosecutors lower estimates, with the estimates of judges lying between. Zalman et al. (2008) replicated Ramsey and Frank’s study and reported very similar opinions for Michigan officials. Neither survey claimed that officials’ estimates were precise measures of wrongful convictions. Zalman et al. (2011) conducted a general residents’ survey in Michigan at the time of their survey of experts and found that among the general population in 2005, the modal category of believed wrongful conviction incidence was 4–5 % and that 61 % of respondents believed that wrongful convictions occurred in between 4 % and 10 % of all felony convictions.

Zalman (2012) provided his own qualitative estimate of wrongful convictions for all felony convictions generally in the United States at a minimum of 0.5–1 %. The qualitative estimate was based primarily on a review of descriptive literature showing widespread defects in the quality of criminal case processing throughout the United States, supplemented by information provided by the precise death penalty wrongful conviction estimates (about 3 %), the validity of qualitative estimation techniques, and the approximations of officials, which are lower than estimates provided by residents in a statewide opinion survey (Zalman et al. 2011). Zalman (2012) concluded that a lower estimate than 0.5 % was highly implausible and that a higher general wrongful conviction rate of 2–3 % was possible, but less plausible than the lower rate. A 1 % wrongful conviction incidence rate would mean that about 10,000 wrongful convictions occur each year in the United States and that about 4,000 of those cases would result in prison sentences.

Estimates of the incidence of wrongful conviction have been contested by critical scholars and criminal justice system personnel who argue that in the absence of firm quantitative data, it can be assumed that decisions made by criminal justice system actors are virtually flawless. Controversy about wrongful conviction rates is not unique to criminal justice. As soon as a social problem becomes a political issue, legislatorsbegin asking for numbers. It then becomes important to distinguish between scientific numbers and political numbers (Jencks 1994). Scholars who study child sexual abuse, for instance, report that there are probably more incentives to hide facts than to reveal them (Tucker and Cheit 2010). Some critical scholars and officials may compare qualitative wrongful conviction estimates to the seeming precision of crime statistics, without being aware of the many difficulties that accompany the development and interpretation of official crime data (Loftin and McDowall 2010). The nature of wrongful convictions and the inherent difficulty of finding them, however, make any attempt to generate a precise quantitative national estimate impossible.

Measuring The Correlates Of Wrongful Convictions

What is known about wrongful convictions is derived from the cases that were discovered by various authors, researchers, and organizations, which then analyzed and catalogued them. Virtually every author or organization identified in the section on “Counting Wrongful Convictions,” and many others, has described the factors associated with false convictions and typically has tallied the frequency with which the correlates of wrongful conviction have occurred.

It is as or more important to measure the correlates of false convictions by deconstructing the original conviction than simply to tally up a case and place it on a wrongful conviction or exoneration list. Examining the facts of a case to determine whether it led to the conviction of an innocent person proceeds simultaneously with determining what factors – errors in an investigation, prosecution, or adjudication – might have been responsible for the miscarriage of justice. Most wrongful conviction studies focus on these correlates. The most prominent sources of wrongful conviction, according to many sources, include eyewitness misidentification combined with suggestive lineup procedures, police tunnel vision that leads investigators to overlook exculpatory evidence, false confessions, reliance on informants and other witnesses who lie, erroneous forensic evidence (as a result of substandard laboratories, use of highly unreliable techniques or judgment errors, and deliberate falsehoods by forensic examiners), prosecutorial error and misconduct (especially the failure to divulge exculpatory evidence to the defense), ineffective assistance of defendant counsel, and such trial errors as misleading forensic science testimony and erroneous or biased judicial evidentiary rulings.

Although the correlates are often called causes of wrongful convictions, they cannot be deemed causal factors in a scientific sense (Gould and Leo 2010). Many errors such as misidentifications or false confessions occur in cases that do not result in convictions (Gross 1987; Drizin and Leo 2004). A handful of studies have compared samples of wrongful convictions to other convictions and have found some of the usual factors to be statistically associated with wrongful convictions but not others (Harmon 2001; Harmon and Lofquist 2005; Garrett 2008; Gross and O’Brien 2008).

Because of the difficulty of matching wrongful conviction cases, which are discovered episodically and often by chance, with a cohort of similar, purportedly accurate convictions, this kind of research is arduous. Nevertheless, such measurements of wrongful convictions are research paths that ought to be pursued by criminologists (Leo 2005).

Another serious limit of false conviction-correlate accounts is that they overgeneralize their findings. For example, many writings claim that eyewitness identification error is the most common wrongful conviction correlated factor. The factors that are discerned in false conviction cases are dependent on the fortuitous discovery of exonerations and wrongful convictions and their unsystematic inclusion in a database. Studies identifying the frequency of correlates should be limited to the particular source of cases and not be extended to wrongful convictions generally. This is recognized by researchers who are aware of the unusual circumstances by which particular groups of cases come into being. Both Garrett (2011), analyzing the first 250 DNA exonerations listed by the Innocence Project, and Gross et al. (2005), analyzing 340 exonerations they discovered, have noted that the cases were an extremely unrepresentative sample of convictions. Almost all resulted from jury trials, whereas more than 95 % of convictions are obtained by guilty pleas. Their samples were almost entirely murder and rape cases, which constitute less than 1 % of all convictions. Thus, Garrett (2011) reports that flawed eyewitness evidence is found in 88 % of his sample, while the 2005 sample of Gross et al. reports such error in 50 % the murder cases and 88 % of the rape cases. Gross (2011) compared the correlates of his expanded exoneration list to the smaller percentage of murder and rape cases found in Gross et al. (2005) or Garrett (2011) and indicated that the proportionate list of correlates has changed. Covey (2011) studied the correlates in two sets of “mass exoneration cases” (which were acknowledged by Gross et al. (2005) and Gross (2011) but were not included in those exoneration lists). Covey discovered that the correlates of error in the wrongful conviction cases among the mass exonerations, virtually all of which were drug or gun possession convictions, were perjury and false confessions, with misidentification playing no role in those wrongful convictions.


The measurement of wrongful convictions is a question asked by all who study the subject (Gross 2008). Providing an answer to a general “how many” question is not easy. The inherent difficulties in discovering wrongful convictions, and governmental resistance and/or inability to identify and list them, hobble a more complete understanding. Nevertheless, precise estimates of wrongful death sentences, combined with a sound overview of the problems within the criminal justice process, lead to a conclusion that the numbers are more than minuscule.

Studies of individual wrongful convictions and lists of miscarriages of justice provide a wealth of information about how they occur, how they are discovered and exonerated, and what factors are correlated with them. A large number of studies by psychologists, legal scholars, and forensic experts are exploring ways to correct criminal justice processing errors, whether or not they directly cause wrongful convictions. Viewing the correlates of wrongful convictions as likely sources of these miscarriages of justice, however, is a sound conjecture. Criminologists can contribute to this research by applying the tools of social science to advance the study of the correlates and causes of wrongful convictions and the relationships among correlates and to more systematically study wrongful convictions in order to clarify our understanding of why errors of justice occur and how to correct them.


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