A few days ago, a New York Times op-ed by Alex Berenson, the author of the forthcoming book Tell Your Children: The Truth About Marijuana, Mental Illness, and Violence, made a startling claim about marijuana legalization, a policy that, as he notes, "seems to be on an unstoppable march [...] in the United States" in light of both national polling on the issue and the many recent, liberalizing changes to state pot laws:
"Because marijuana can cause paranoia and psychosis, and those conditions are closely linked to violence[,] it appears to lead to an increase in violent crime. Before recreational legalization began in 2014, advocates promised that it would reduce violent crime. But the first four states to legalize -- Alaska, Colorado, Oregon and Washington -- have seen sharp increases in murders and aggravated assaults since 2014, according to reports from the Federal Bureau of Investigation. Police reports and news articles show a clear link to cannabis in many cases."
Let's set aside the idea that legalizing marijuana will reduce violent crime: violent crime is unpredictable and this is probably too optimistic a claim to pin to any one change in the law not geared directly at crime reduction (though it's not crazy to imagine that obviating black markets might reduce crime in certain instances). Berenson isn't just expressing skepticism of that claim -- he's arguing, in strong language, that legalization has done the opposite. And if, in fact, there were a tight, clearly illustrated link between cannabis legalization and increases in violent crime, that would certainly be an important bit of evidence to consider as legalization continues. But Berenson doesn't come close to showing this. Rather, this paragraph is a case study in how to misleadingly use statistics to make oversimplified arguments about human behavior and public policy.
At root, Berenson's fishiest move is his choice of 2014 as a baseline year. "Nothing interesting happened with regard to pot in 2014," said Mark Kleiman, a drug expert and public-policy professor at NYU who has himself urged caution over marijuana-legalization Pollyannaish-ness, in an email, "but there was a national uptick in homicide in 2015?2016."
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Plenty of states, carried along by the nationwide trend, saw increases in violent crime, whatever their pot laws. And as Kleiman noted, there's no reason to pick 2014 as a year for examining the four states in question. While Alaska and Oregon did officially legalize marijuana then, Colorado and Washington did so in 2012. And state pot-law histories tend to be more complicated than the dates of full legalization, anyway -- in Alaska and Oregon (see the previous links), it's been decades since having small to moderate amounts of marijuana for personal use could lead to anything worse than a small fine. The idea that a state flipping over from a very liberal pot policy to a very liberal pot policy would lead to an immediate uptick in violent crime demands evidence that's absent from Berenson's column.
Otherwise we would have legalisation all around the globe...