Radley Balko attempts to calculate how often we send an innocent person to prison:
The Innocence Project cites a study by Seton Hall's D. Michael Risinger that puts the percentage of innocents in prison at 3 to 5 percent. But that study looked only at capital crimes, and there's yet more debate over whether data gleaned from those accused of crimes that are eligible for the death penalty would translate into higher or lower wrongful conviction rates for those accused of lesser crimes. (Those who argue that it would be higher note that there's more pressure on prosecutors and jurors to hold someone accountable in murder cases. On the other hand, defendants tend to have better representation in capital cases.) But even dropping below the study's floor, using the 2008 prison population, a 2 percent wrongful conviction rate would mean about 46,000 people incarcerated for crimes they didn't commit.