Deliberately conservative figure lays bare extent of possible miscarriages of justice suggesting that the innocence of more than 200 prisoners still in the system may never be recognised 
 
 At least 4.1% of all defendants sentenced to death in the US in the modern era are innocent, according to the first major study to attempt to calculate how often states get it wrong in their wielding of the ultimate punishment. 
 
 
 
 A team of legal experts and statisticians from Michigan and Pennsylvania used the latest statistical techniques to produce a peer-reviewed estimate of the “dark figure” that lies behind the death penalty – how many of the more than 8,000 men and women who have been put on death row since the 1970s were falsely convicted. 
 
 The team arrived at a deliberately conservative figure that lays bare the extent of possible miscarriages of justice, suggesting that the innocence of more than 200 prisoners still in the system may never be recognised. 
 
 The study concludes that were all innocent people who were given death sentences to be cleared of their offences, the exoneration rate would rise from the actual rate of those released – 1.6% – to at least 4.1%. That is equivalent in the time frame of the study, 1973 to 2004, of about 340 prisoners – a much larger group than the 138 who were exonerated in the same period. 
 
 “This is a disturbing finding,” said Samuel Gross, a law professor at the University of Michigan law school who is the lead author of the research. “There are a large number of people who are sentenced to death, and despite our best efforts some of them have undoubtedly been executed.” 
 
 The research team deployed statistical devices to put a figure on the proportion of cases of hidden innocence. In particular, they deployed a technique known as “survival analysis”, to calculate the percentage of prisoners who have been taken off death row but who might still be innocent. 
 
 They also applied “sensitivity analysis”, to take into account possible cases of exonerations where the released prisoner is nonetheless guilty, and to ensure that the overall findings erred on the side of caution. 
 
 The study, published in a prestigious journal, the Proceedings of the National Academy of Sciences, does not solve perhaps the greatest single riddle of the death penalty: how many innocent people have actually been put to death in modern times. That remains a haunting unknown. 
 
 But Gross is clear that such final and irreparable injustices have occured. 
 
 “If you look at the numbers in our study, at how many errors are made, then you cannot believe that we haven’t executed any innocent person – that would be wishful thinking.” 
 
 Richard Dieter, executive director of the Death Penalty Information Center, which supplied some of the data on which the study depends, said “every time we have an execution, there is a risk of executing an innocent person. The risk may be small, but it’s unacceptable”. 
 
 The ballpark figure of at least 4.1% innocence is higher than previous studies looking at exoneration rates that had smaller sample sizes and were more restricted in their remit. It is also considerably higher than the estimate given in 2007 by the conservative US supreme court justice Antonin Scalia, who wrote that American criminal convictions generally had an “error rate of .027% – or, to put it another way, a success rate of 99.973%”. 
 
 The authors comment tartly with respect to Scalia’s skills as a statistician: “That would be comforting, if true. In fact, the claim is silly.” 
 
 The single largest group of innocent death row inmates are neither exonerated and released nor executed, the study suggests. Rather, they are left in limbo, somewhere in between those two extremes of fortune. 
 
 Gross and his co-authors estimate that 36% of all those sentenced to death between 1973 and 2004 – some 2,675 people – were taken off death row after doubts about their convictions were raised. But they were then put on new sentences, usually life without parole, that mean they will almost certainly die in prison. 
 
 The study concludes chillingly that “the great majority of innocent defendants who are convicted of capital murder in the United States are neither executed nor exonerated. They are sentenced, or resentenced to prison for life, and then forgotten”. 
 
 Gross said that this explains the 200 or so missing people highlighted by his study – men and women who are innocent and yet have not been exonerated. In most cases, they have probably been moved off death row. 
 
 Because they are no longer under the threat of execution, they are no longer treated as priorities within the criminal justice system. They can no longer draw upon the help of experienced legal teams, and they may not be entitled to appeals. As a result, their chances of clearing their names plummet. 
 
 “The best efforts of the judicial system are only devoted to prisoners when they face execution,” Gross said. “In many cases when people are released from death row, little or nothing is done to deal with the equally bad injustice they now face – that they will spend the rest of their lives in prison for a crime they didn’t commit.” ||||| Just how many individuals on death row are incorrectly convicted? The question has dogged attorneys and civil rights advocates for years, but a simple answer is almost impossible because few wrongful cases are ever overturned. A new analysis is adding a level of much-needed detail, and it concludes that more than twice as many inmates were wrongly convicted and sentenced to death than have been exonerated and freed. 
 
 
 
 Borrowing a statistical method often used to evaluate whether new medical therapies help patients survive, a team of researchers has concluded that about 4.1 percent of criminal defendants who are sentenced to death are falsely convicted. The approach allows researchers to “actually come up with a valid estimate of the rate of false convictions—knowing something that people say [in criminal justice] is not knowable,” says study author Samuel Gross, a law professor at the University of Michigan Law School and editor of the National Registry of Exonerations, a U.S.-focused exoneration database. What makes the analysis possible is that data on the potential need for exoneration from death penalty cases come to light more often than it does for other types of criminal proceedings. All death sentences in the U.S. are based on crimes that include homicide. 
 
 
 
 The study, led by a team of lawyers and statisticians, examined data on both 7,482 defendants who were given death sentences between 1973 and 2004 and death row exonerations during that time. By applying survival analysis—a statistical method often used to calculate how well new treatments help patients survive—they determined how often a prisoner under threat of execution was exonerated. The method usually tracks patients to see if a new therapy prolongs the period of time until a person dies from the illness in question but it can also be applied to policy questions that have clear end points. In this study the end point of tracking was exoneration (being found innocent and freed) or the actual execution. “Survival” was defined as remaining in prison. The “therapy” here would be removal of the threat of execution. 
 
 
 
 Here’s how their analysis works. It says that if all death-sentenced defendants remained under this sentence indefinitely, as opposed to being taken off death row due to being resentenced to life in prison or their fate being artificially cut off by the study ending, then 4.1 percent of those prisoners would have otherwise been exonerated. (And being exonerated and freed by legal action here is used as the best proxy for innocence.) The analysis also takes into account other occurrences such as suicide or death of a prisoner from natural causes. The number of false convictions among the death-sentenced has been particularly hard to estimate, Gross says, because many prisoners who are on death row are eventually moved off of it but remain in prison, which often reduces their chances of exoneration. 
 
 
 
 The issue affects a significant number of people. Since 1973 144 death-sentenced defendants have been exonerated in the U.S. But Gross says that the analysis indicates that at least 340 people would have been put to death unjustly in that same time period. “There are no other reliable estimates of the rate of false conviction in any context,” the researchers wrote in the study, published online on April 28 in Proceedings of the National Academy of Sciences. 
 
 
 
 The researchers also note that a 4.1 percent rate of false conviction is conservative, given that separate calculations gauging the accuracy of the assumptions that took an even more conservative stance—assuming that people who were executed had zero chance of false conviction and that the chances of exoneration after retrial would be twice that of people on death row—would still produce a larger figure than their 4.1 percent estimate. Although their analysis does not include data after 2004, the researchers note that they doubt that the use of DNA identification technology would have much impact on false conviction rates—because DNA evidence is primarily used in cases such as rape rather than homicide. Only about 13 percent of death row exonerations have resulted from DNA testing. 
 
 
 
 For more on death penalty considerations, see Scientific American’s editorial in the May edition of the magazine that details how the use of drugs to carry out capital punishment is inadvertently putting medical patients at risk.
– At least 4.1% of people sentenced to death in the US are innocent, a new report warns—and most of them end up neither executed nor exonerated, but serving life behind bars. Researchers say that at a conservative estimate, one in 25 of the thousands of people condemned to death between 1973 and 2004 is innocent and while 138 were exonerated and some were almost certainly executed, up to 200 were taken off death row and are serving life for murders they didn't commit, the Guardian reports. The researchers—who employed a statistical method often used to assess survival rates of patients treated with new medical therapies—say being moved off death row tends to reduce the chances of exoneration, as the inmates' cases are no longer treated as priorities and they have fewer options for appeals, Scientific American reports. "The great majority of innocent defendants who are convicted of capital murder in the United States are neither executed nor exonerated," the study concludes. "They are sentenced, or re-sentenced to prison for life, and then forgotten."