Over 4 percent of people sentenced to death are innocent, according to what authors of a report published Monday say was a “conservative,” statistics-based estimate.

Advocates against the death penalty told Al Jazeera that number is astoundingly high. But for one exonerated death row inmate, the figure seems incredibly low — and he believes he’s more qualified to estimate the number of innocents on death row than professors and analysts.

“I feel like the number is much higher, being that I’ve been there,” Reggie Griffin, who was sentenced to death for allegedly killing another inmate in 1988, told Al Jazeera. For four years, he thought he would die at the hands of the state, but his sentence was eventually reduced.

A Missouri judge ruled on Oct. 25, 2013, that the two inmates who had testified against Griffin had not provided sufficient evidence against him. One of the inmates had recanted his testimony, saying that he had testified against Griffin because prison guards said they would protect him from systematic sexual abuse at Missouri’s Moberly prison.

Monday's report, published by the National Academy of Sciences, determined that 4.1 percent of inmates sentenced to death row are innocent. It reaches this conclusion by calculating how many former death row inmates whose sentences were reduced would be exonerated if they were deemed innocent at the same rate as inmates still on death row.

Findings show it is exponentially less likely for former death row inmates like Griffin, who waited for over a decade to be released, to be exonerated in cases where they are innocent.

Most death row defendants’ sentences — likely close to two-thirds — are either commuted to life imprisonment or somehow overturned. But once inmates are taken off death row, they are less than one-tenth as likely to be exonerated, according to the report.

That’s because media, civil society and legal groups tend to spend more resources on death row inmates than people whose sentences have been reduced to life in prison, lead author on the report and University of Michigan law professor Samuel R. Gross told Al Jazeera.

“If we were to invest the effort by judges, prosecutors, journalists — if the entire system were as worried and upset to prevent people from being executed as they were to prevent people from being in prison for their entire lives, we’d find many more who are innocent,” Gross said.

Richard Dieter, director of the Death Penalty Information Center, said American society must pay more attention to death row inmates whose sentences are reduced.

“The much larger class of cases are people who were on death row and spend the rest of their lives in prison, but they were innocent,” Dieter said. He said the death penalty “distorts” what is otherwise a rational legal process.

“It’s more theater and symbol than a rational process that attempts to arrive at the truth and the best resolution of the case,” he said. “The death penalty means it’s high stakes for both sides” — for the prosecution to win or at least avoid an “embarrassing” exoneration and for the defense to save a life. Death penalty cases therefore garner much more public attention.

Those whose sentences are reduced to life in prison are often considered “lucky,” Dieter added.