There is No Way to Know How Many Innocent People are in Prison

From NYTimes.com: A couple of years ago, Justice Antonin Scalia, concurring in a Supreme Court death penalty decision, took stock of the American criminal justice system and pronounced himself satisfied. The rate at which innocent people are convicted of felonies is, he said, less than three-hundredths of 1 percent — .027 percent, to be exact.

That rate, he said, is acceptable. “One cannot have a system of criminal punishment without accepting the possibility that someone will be punished mistakenly,” he wrote. “That is a truism, not a revelation.”

But there is reason to question Justice Scalia’s math. He had, citing the methodology of an Oregon prosecutor, divided an estimate of the number of exonerated prisoners, almost all of them in murder and rape cases, by the total of all felony convictions.

“By this logic,” Samuel R. Gross, a law professor at the University of Michigan, wrote in a response to be published in this year’s Annual Review of Law and Social Science, “we could estimate the proportion of baseball players who’ve used steroids by dividing the number of major league players who’ve been caught by the total of all baseball players at all levels: major league, minor league, semipro, college and Little League — and maybe throwing in football and basketball players as well.”

Joshua Marquis, the Oregon prosecutor cited by Justice Scalia, granted the logic of Professor Gross’s critique but not his conclusion.

“He correctly points out,” Mr. Marquis, the district attorney in Clatsop County, Ore., said of Professor Gross, “that rape and murders are only a small percentage of all crimes, but then has absolutely no real data to suggest there are epidemic false convictions in, say, burglary cases.”

What the debate demonstrates is that we know almost nothing about the number of innocent people in prison. That is because any effort to estimate it involves extrapolation from just two numbers, neither one satisfactory. Rest of Article. . . [Mark Godsey]