A study authored by Samuel Gross, a professor from University of Michigan Law School, and others suggests that several of the 1,320 people executed in the United States since 1977 were likely innocent. The following is from a Washington Post article on the subject:
“Gross and three other researchers, including a biostatistics expert, looked at the issue using a technique often used in medical studies called survival analysis. Yale University biostatistics expert Theodore Holford, who wasn’t part of the study, said the work done by Gross ‘seems to be a reasonable way to look at these data.’
“Because of various assumptions, it might be best to use the margin of error in the study and say the innocence rate is probably between 2.8 percent and 5.2 percent, said University of South Carolina statistics professor John Grego, who wasn’t part of the study.
“The study is the first to use solid and appropriate statistical methods to address questions of exoneration or false convictions, an important subject, said Columbia Law School professor Jeffrey Fagan, who also is a professor of epidemiology at the Mailman School of Public Health. The research combines data from three independent sources, a rigorous approach used by few studies on capital punishment, he said.”
While the authors conclude that this percentage is relatively low, their findings provide additional support for the concept that innocent people have been and will continue to be put to death in the United States as long as the death penalty is an option.