A Simple Chart That Shows We’ve Locked Up Too Many People

Facts matter: Sign up for the free Mother Jones Daily newsletter. Support our nonprofit reporting. Subscribe to our print magazine.


Correlation is not causation. This has recently become something of an all-purpose comeback from people who want to sound smart without really understanding anything about a particular research result. Still, whether it’s overused or not, it’s a true statement. When two things move up and down together, it’s a hint that one of them might be causing the other, but it’s just a hint. Sometimes correlation implies causation and sometimes it doesn’t.

The inverse statement, however, is different: If there’s no correlation, then there’s no causation. With the rarest of exceptions, this is almost always true. Dara Lind provides an example of this as it relates to crime and mass incarceration.

The chart on the right shows the trend in various states at reducing incarceration. If reducing incarceration produced more crime, you’d expect at least some level of correlation. The dots would line up to look something like the red arrow, with lots of dots in the upper left quadrant.

Obviously we see nothing like that. In fact, we don’t appear to see any significant correlation at all. As Lind says, the scatterplot is just a scatter.

It’s possible that a more sophisticated analysis would tease out a correlation of some kind. You can show almost anything if you really put your mind to it. But if a simple, crude scatterplot doesn’t show even a hint of a correlation, it’s almost a certainty that there’s nothing there. And in this case it demonstrates that we’ve locked up too many people. Mass incarceration hit the limit of its effectiveness in the late-80s and since then has been running dangerously on autopilot. It ruins lives, costs a lot of money, and has gone way beyond the point where it affects the crime rate. It’s well past time to reverse this trend and get to work seriously cutting the prison population.

THE TRUTH...

is the first thing despots go after. An unwavering commitment to it is probably what draws you to Mother Jones' journalism. And as we're seeing in the US and the world around, authoritarians seek to poison the discourse and the way we relate to each other because they can't stand people coming together around a shared sense of the truth—it's a huge threat to them.

Which is also a pretty great way to describe Mother Jones' mission: People coming together around the truth to hold power accountable.

And right now, we need to raise about $400,000 from our online readers over the next two months to hit our annual goal and make good on that mission. Read more about the information war we find ourselves in and how people-powered, independent reporting can and must rise to the challenge—and please support our team's truth-telling journalism with a donation if you can right now.

payment methods

THE TRUTH...

is the first thing despots go after. An unwavering commitment to it is probably what draws you to Mother Jones' journalism. And as we're seeing in the US and the world around, authoritarians seek to poison the discourse and the way we relate to each other because they can't stand people coming together around a shared sense of the truth—it's a huge threat to them.

Which is also a pretty great way to describe Mother Jones' mission: People coming together around the truth to hold power accountable.

And right now, we need to raise about $400,000 from our online readers over the next two months to hit our annual goal and make good on that mission. Read more about the information war we find ourselves in and how people-powered, independent reporting can and must rise to the challenge—and please support our team's truth-telling journalism with a donation if you can right now.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate