Approximately 1 in every 25 death row inmates in America are likely to be innocent, according to a new study published in The Proceedings of the National Academy of Sciences.

The study draws its information from data that has been acquired over the course of years. The authors state that 1.6 percent of people put on death row since 1973 were exonerated, reports The Week. Since many death row defendants get taken off death row and instead given a life sentence, the exoneration rate drops.

Using a statistical technique called survival analysis, the authors estimated that if all death row inmates were to stay indefinitely on death row, at least 4.1% would be exonerated. They believe this is the number of false convictions in the US.

“The great majority of innocent people who are sentenced to death are never identified and freed,” said the lead author of the study, Professor Samuel R. Gross of the University of Michigan Law School, according to The Kansas City Star. “The purpose of our study is to account for the innocent defendants who are not exonerated.”