Iain Murray is upset that Reuters has misreported the RAND “gateway” study. (Much less upset, I can assure you, than the study’s authors.) As noted before in this space, the study used simulation techniques to show that the observed correlation between cannabis use and use of harder drugs could be explained without invoking any causal link between the two. It did not do what the Reuters story claimed it did: show that the “gateway effect” did not exist.
But I think that Iain Murray, who for other reasons is a strong advocate of maintaining cannabis prohibition, overstates his case when he says:
The researchers have only offered an alternative explanation, not disproved the gateway theory. The gateway question needs to be answered. It has not been yet.
To which I would respond: What question? The gateway effect was proposed as an explanation for a set of observed phenomena: the strong correlation between cannabis use and subsequent use of other drugs. Morral et al. have now managed to explain that correlation more parsimoniously, without invoking any gateway effect. That leaves us with no reason to believe that the gateway effect exists. Unless someone can point to phenomena for which the gateway effect is the most parsimonious explanation, it’s time to send the gateway theory to the compost heap.
After all, Einstein never proved that the luminiferous aether didn’t exist: he just managed to explain all of the observed electromagnetic phenomena without invoking it. It will be a fine day when policy advocates are as willing as scientists to shave with Occam’s Razor.