The U.S. incarcerated population is the lowest it's been in more than a decade, according to the most recent numbers.
Just under 2.2 million people were in local, state and federal prisons at the end of 2015.
That's about a 51,000-person drop from 2014 and the lowest it's been since 2004.
And it's no accident. Many states have started to change correction policies, including preventing repeat offenders.
And some states have seen a drop in crime rates. In the 10 states where imprisonment dropped the most, the crime rate fell by more than 14 percent.
But it's also important to point out that states with the highest crime rate increases also saw imprisonment rates go down. And several states that increased imprisonment saw crime rates go down.
Editor's note: This story has been updated to clarify that researchers believe there's no correlation between reductions in crime and reductions in imprisonment rates.
