A new study estimates that at least one in 25 people sentenced to death in the United States are innocent.
Researcher Samuel Gross of University of Michigan Law School and colleagues published the analysis in April issue’s early online edition of the research journal Proceedings of the National Academy of Sciences.
Some researchers have held that the rate of false convictions is unknowable since, if there were some systematic way to determine conviction accuracy, errors wouldn’t occur in the first place. In the absence of hard data, some have claimed the false-conviction rate is almost zero.
Gross and colleagues focused on death sentences, which have a far higher exoneration rate than other sentences. “A high proportion of false convictions that do come to light and produce exonerations are concentrated among the tiny minority of cases in which defendants are sentenced to death,” they wrote. “This makes it possible to use data on death row exonerations to estimate the overall rate of false conviction among death sentences.”
Noting that most death-sentenced defendants are re-sentenced to life in prison and don’t stay on death row, the researchers analyzed exonerations from 1973, when the United States established the death penalty in its modern form, to 2004.
Their data came from the Department of Justice and the Death Penalty Information Center, a nonprofit that tracks exonerations among capital defendants.
In terms of actual exonerations, “2.3% of all death sentences imposed from 1973 through 1989 resulted in exoneration by the end of 2004,” the researchers wrote. But the exoneration rate becomes much lower for defendants re-sentenced to life in prison, they noted. Using “survival analysis,” a technique from epidemiology, they estimated that if all death-sentenced defendants had stayed under execution threat for 21 years, at least 4.1 percent would have been exonerated.
Of course, they added, the study must contain errors—such as by not accounting for the exonerations, unknown in number, that must also be erroneous. But Gross and colleagues claimed their work makes “conservative assumptions” overall.
Source : http://www.world-science.net/