Shawn Vestal: Rechecking the stats on pot and violence

January 11, 2019

Has legal pot ushered in a more violent era in Washington?

This is the possibility put forth in a new book and New Yorker article that used our state’s recent rise in the rate of murder and aggravated assault to hint at potential links between violent behavior and marijuana use.

The New Yorker piece was written by Malcolm Gladwell – the popular science writer and lightning rod who frequently draws criticism for elevating the hints and possibilities of scientific research into absolute natural laws. It was based in part on a new book by former New York Times reporter Alex Berenson, “Tell Your Children.”

“Between 2013 and 2017, the state’s murder and aggravated assault rates rose forty per cent – twice the national homicide increase and four times the national aggravated assault increase,” Gladwell writes.

“We don’t know that an increase in cannabis use was responsible for that surge in violence. Berenson, though, finds it strange that, at a time when Washington may have exposed its population to higher levels of what is widely assumed to be a calming substance, its citizens began turning on one another with increased aggression.”

Talk about your drive-by caveat. That “we don’t know” deserves a whole lot more weight. Maybe all the weight. Because, while there have been increases in violent crime here in recent years, there is not yet any reason to draw a connection to legal weed.

Further, the statistics on violent crime in Washington – as reported by local law enforcement agencies to the FBI’s Uniform Crime Reporting program – simply do not align with Gladwell’s assertions.

Washington’s murder rate has long been well below the national average. If you look at a chart over the past 20 years, what you see is a wave bumping up and down between 2.3 and 3.3 murders per 100,000 people.

In the years Gladwell cites, our murder rate increased by a margin of 0.8 murders per 100,000 residents, to an overall rate of 3.1, according to UCR-based Crime Data Explorer online.

That’s a 35 percent increase.

The national murder rate rose in those years by a margin of 0.8 murders per 100,000 residents, to an overall rate of 5.3.

That’s an 18 percent increase.

Must be the marijuana.

Meanwhile, aggravated assaults have followed the same pattern here that they have nationally – rising slightly in recent years after long, steady decline. The national rate rose by a margin of 19.3 per 100,000 between 2013 and 2017; Washington’s rose by 17.9 per 100,000.

Again, because Washington has long had a significantly lower crime rate to begin with, the percentage change is higher here – 11 percent in Washington, compared to 8 percent nationally.

That’s a pretty sharp discrepancy with Gladwell’s characterization of 40 percent increases that are four times larger than the national rise. In an email, Berenson said that he used the same figures and percentage increases in his book that I’m using here; he said he wasn’t sure why Gladwell reported larger increases. I tried to contact Gladwell via social media Thursday without immediate success.

Berenson’s book argues, as does Gladwell’s article, that we need to know more about potential links between mental illness, violence and marijuana use, and lays out some of the suggestive case that such links are plausible. They also argue that we have – in our widespread cultural acceptance of marijuana as essentially harmless – failed to take potential problems seriously.

All of which may well be true. But dragooning Washington’s murder rate into the argument is pulling a Stretch Armstrong on the facts, twisting correlation into causation. Changes in crime rates are complex and difficult to explain simply, and this particular explanation is, at this point at least, far too simple.

One might just as easily select another set of statistics to prove the opposite point: The overall rate of violent crime in Washington state – including all crimes against people, and not just murder and aggravated assault – increased 5 percent between 2013 and 2017, compared to 7 percent nationwide.

In other words, since marijuana was legalized, violent crime across the nation has risen 40 percent more than violent crime in Washington state.

Should we credit marijuana?