I also thought the study was convincing in showing a significant correlation*
It’s been folk belief for a long time that pot makes you slow, unmotivated, and dumb.
Therefore, I can’t rule out that the study failed to control for giving a shit about one’s mental abilities, a factor that’s nearly certain to explain the outcome by a sum of all possible intermediaries, of which pot is just one.
[*] even though the number of people in the 8+ IQ point losing population seemed to be only about N=30. 1-2 IQ points difference is probably not significant, but I’m guessing N was larger, so maybe. Also, the same data set was mined for genetic correlates with heavy pot use, so they could have easily controlled for that (could turn out that e.g. the same factors cause persistent pot use and adulthood cognitive degeneration, though I judge that unlikely). Since there is so much demand from the DARE set for a finding like this, you also have to expect quite a lot of publication bias and population-cherry-picking, as well.
I also thought the study was convincing in showing a significant correlation*
It’s been folk belief for a long time that pot makes you slow, unmotivated, and dumb.
Therefore, I can’t rule out that the study failed to control for giving a shit about one’s mental abilities, a factor that’s nearly certain to explain the outcome by a sum of all possible intermediaries, of which pot is just one.
[*] even though the number of people in the 8+ IQ point losing population seemed to be only about N=30. 1-2 IQ points difference is probably not significant, but I’m guessing N was larger, so maybe. Also, the same data set was mined for genetic correlates with heavy pot use, so they could have easily controlled for that (could turn out that e.g. the same factors cause persistent pot use and adulthood cognitive degeneration, though I judge that unlikely). Since there is so much demand from the DARE set for a finding like this, you also have to expect quite a lot of publication bias and population-cherry-picking, as well.