Imprisonment Rate Down, But Why?

The U.S. Bureau of Justice Statistics has released its annual report on prisoners for 2019. The “imprisonment rate,” defined as number of sentenced prisoners per 100,000 population, continued to decline, as it has since peaking in 2007.

While many people obsess about the imprisonment rate, I consider it to be a statistic of little value, at least by itself. Why is it down? Is it down because crime is down? Because legislatures lowered statutory penalties? Because prosecutors use their discretion not to charge every crime a defendant has committed more often? Because judges use their discretion in sentencing more leniently?

If legislative, executive, and judicial policies were all constant, we would expect a relation between crime rates and incarceration rates, but we would not expect them to follow in lock step. There would be a lag between cause and effect. Defendants are not sentenced for serious crimes immediately. Trial and sentencing often do not happen in the same year as the crime. Once sentenced, the perpetrators will remain in the numerator of the “imprisonment rate” for some time.

In his 2017 book Locked In: The True Causes of Mass Incarceration and How to Achieve Real Reform, academic/advocate John Pfaff noted the curious fact that the incarceration rate for violent crime had dropped in 2013, even though all of the “reform” efforts to that date had focused on nonviolent offenders. He also noted a curious lack of interest in this fact among people studying incarceration rates. This is discussed in part III of my review of Pfaff’s book, Refreshing Candor, Useful Data, and a Dog’s Breakfast of Proposals: A Review of Locked In by John Pfaff, 20 Fed. Soc. Rev. 124, 134-136 (2019).

But to the extent that the drop in incarceration rate is the result of “reforms” that have gone too far in the direction of leniency, these “reforms” may be setting the stage for increased crime rates which will eventually result in a turnaround and increase in incarceration rates.

In physics we call this “harmonic motion.” If a pendulum is displaced from the center position, gravity pulls it down but also speeds it up. That momentum causes it to blow through the center position and move to the other side, rising as it does until gravity pulls it back down again. A cause produces an effect which becomes a cause in the other direction, and on it goes. We could be coming out of the low point of a cycle, to be followed by increased crime rates and eventually demands for tougher policies.