As we've written, research shows that the rise of mass incarceration in America deserves very little (if any) credit for the stunning drop in crime over the last 25 years. The FBI's Uniform Crime Report provides evidence that the reverse is also true. Reducing prison populations — as several states and the federal government have done over the last few years — doesn't have any effect on crime rates.

An analysis by the Pew Public Safety Performance Project found that the states that shrunk their incarceration rates the most over the last five years experienced a slightly bigger drop in crime as the states where incarceration rates grew: 12 percent versus 10 percent.

What about all fifty states? We made a scatterplot based on Pew's data, mapping how a state's imprisonment rate changed from 2008-2013 on the horizontal x axis, and how its crime rate changed on the vertical y axis. The result is, well, a scatter — there's no clear relationship at all between prison and crime. That makes it a lot harder to justify the US' current level of incarceration.