Weed Makes A Bad Study Buddy

Last week, Christopher Ingraham covered a Lancet study connecting teen pot use to school graduation rates:

Teenagers who smoke marijuana daily are over 60 percent less likely to complete high school than those who never use. They’re also 60 percent less likely to graduate college and seven times more likely to attempt suicide.

But yesterday he qualified those findings:

From 2006 to 2012, monthly marijuana use among high school seniors increased by more than 4 percentage points*, from 18.3 percent to 22.9 percent. If indeed marijuana use were the educational catastrophe that opponents predict, you’d expect to see downward pressure on national graduation rates as more kids took up the habit. But in actuality, the opposite happened: over the same period, as kids were smoking more, graduation rates jumped 8 percentage points.

This should not be at all construed to imply that increasing rates of marijuana use are somehow causing higher graduation rates. Correlation doesn’t equal causation. And these numbers don’t even constitute an argument against the Lancet study findings – it’s perfectly plausible that any negative consequences of marijuana use are too small to show up in a simple national trendline like this.

But it’s a useful corrective against the facile notion that “more weed = less graduation.”

Jacob Sullum inserts further caveats:

It surely is plausible that teenagers who get stoned every day, like teenagers who get drunk every day, would have trouble doing well in school because they are intoxicated when they are supposed to be learning. But that observation leaves unanswered the question of why some teenagers, but not others, choose to get stoned every day. The propensity to engage in that sort of behavior may be a marker for characteristics that independently undermine academic performance.