Wrongful convictions, a staple of Hollywood movies, crime shows, and books alike, aren’t quite as common in the real world. Until very recently, the number of wrongful convictions was assumed to be 0.027%. It was such a widely noted statistic that the late U.S. Supreme Court Justice Antonin Scalia included it in a concurring opinion in 2006.
That number comes from a NY Times op-ed piece, written by Clatsop County, Oregon District Attorney Joshua Marquis. In it, he cites a study led by University of Michigan law professor Samuel Gross that found 340 inmates, almost all of whom were convicted in rape and murder cases, who were exonerated between 1989 and 2003. Marquis compared those 340 cases to the approximately 15 million felony convictions over that 15 year stretch. “That would make the error rate .027 percent - or, to put it another way, a success rate of 99.973 percent,” he said.
In 2014, Gross published a new study, this time refining his search parameters just to death row inmates. He stated that the lack of a method to determine the accuracy of criminal convictions results in very few discoveries of false convictions, and those discoveries that lead to exonerations are disproportionately concentrated among inmates on death row.
“We use survival analysis to model this effect, and estimate that if all death-sentenced defendants remained under sentence of death indefinitely, at least 4.1% would be exonerated. We conclude that this is a conservative estimate of the proportion of false conviction among death sentences in the United States.”
Gross and his research team argued that, while their study only focused on less than 0.1% of prison sentences, these cases received an increased level of scrutiny due to the severity of the punishment. Given the amount of resources spent on cases of capital punishment, the researchers reason that it’s likely that a falsely convicted inmate on death row will be exonerated. They believe that their calculations, when applied to all felony convictions - the vast majority of which receive minimal scrutiny – gives a realistic estimate of false conviction rates.
Compounding this issue is the fact that less than half of the people who are found guilty of murder end up on death row; rather, they end up serving life in prison. Given the results from Gross’ study, it’s reasonable to assume that there are at least several hundred innocent people serving life in prison. When you factor in a report released by the American Civil Liberties Union that found black people were 3.7 times more likely to be arrested than white people for marijuana possession despite comparable usage rates, that 4.1% found in the study begins to look like it might be a low estimate