Over the past week, prominent political figures from both sides of the aisle have suggested that the prohibition of marijuana is to blame for mass incarceration.

Former House Speaker John Boehner, a Republican from Ohio, claimed, “When you look at the number of people in our state and federal penitentiaries, who are there for possession of small amounts of cannabis, you begin to really scratch your head. We have literally filled up our jails with people who are nonviolent and frankly do not belong there.” Sen. Brian Schatz, a Democrat from Hawaii, tweeted, “More than 2 million in jail, mostly black and brown, many for holding a small amount of marijuana.”

The suggestion, however, is wrong.

It is true that a lot of people are arrested each year for marijuana. In 2016, nearly 600,000 people were arrested for simple marijuana possession. These arrests on their own can create huge problems — leading to criminal records that can make it harder to get a job, housing, or financial aid for college.

But these arrests are only a small part of America’s mass incarceration problem.

First, most people in jail or prison are not in for drug charges at all. According to the Prison Policy Initiative, around 21 percent of people in jail or prison are in there for a drug crime, including marijuana possession. So the great majority of people are not incarcerated due to drugs. And, contrary to Boehner’s claim about nonviolent offenders, about 42 percent of people in jail or prison are in there for violent crimes — making violent offenses the single biggest driver of incarceration out of all offense categories.

How many of the 21 percent of drug offenders are in for marijuana possession?

Unfortunately, we don’t have good data for jails, where people are held before they’re convicted of a crime and for shorter sentences. But based on the Prison Policy Initiative’s data, a quarter of people held in local jails are in on drug charges — far from a majority. And as Fordham University criminal justice expert John Pfaff noted on Twitter, chances are only a fraction of those drug offenders were nabbed on marijuana charges instead of charges for all sorts of other drugs.

We also don’t have good data for state prisons — where more than 87 percent of US prison inmates are held, based on federal data. But we do know that a minority of state prisoners are in for drugs: In 2015, 3.4 percent of all state prisoners were in for drug possession and 11.7 percent were in for other drug-related crimes. So, again, only a fraction of prisoners are locked up due to drug prohibition in general, much less marijuana prohibition in particular.

We do have some good data for the federal system. According to the US Sentencing Commission, 92 of nearly 20,000 people — fewer than half a percent — sentenced for drug offenses during fiscal year 2017 were locked up due to simple possession of marijuana. And drug cases made up less than a third of cases reported by the Sentencing Commission that year. Not all of these people were sentenced to prison; some got probation instead.

Since the federal system is focused much more on drug trafficking than the state system, it’s not really possible to extrapolate the federal numbers to state prisons.

Based on the data we do have, though, it’s fair to say that marijuana prohibition — and even the war on drugs more broadly — is not the major driver of mass incarceration.

For more on these topics, read Vox’s explainers on mass incarceration and marijuana legalization.