Do you ever fall asleep with your shoes on and wake up with a headache? A lot of people do – in fact, there’s plenty of evidence that people who go to sleep in their shoes have headaches when they wake. Of course, most headaches aren’t caused by sleeping in shoes, so it must be the other way round, mustn’t it? Falling asleep in your shoes causes headaches.

Er, no. It’s just a hunch, but I suspect some other common factor may be involved in the correlation.

So how about this? Over the past 200 years, the number of pirates sailing the seas has fallen steadily. At the same time, average global temperatures have risen. In fact, if the assumed number of pirates and the observed global warming are considered together, the graphs show a clear relationship: as one goes down the other goes up.

So what we need to combat global warming is more pirates – right?

Well no, obviously. Correlation, as we keep saying (and people everywhere keep forgetting), is not causation.


It’s a bit more complicated than that


Nevertheless, it’s beyond tempting to see a meaningful pattern in the figures published recently by the polling firm Gallup showing that US adults (particularly the younger ones) are smoking less tobacco and using more cannabis. So does this mean the rise in cannabis is causing tobacco to fall in popularity, or is it the other way round? Or is it, in fact, more complicated than either of those suggestions?

Gallup’s senior editor Jeff Jones is, quite rightly, very careful not to draw any of those conclusions.

“From a purely statistical perspective, there is a correlation because cannabis usage is trending up and cigarette usage trending down among young adults,” he said. “But the correlation here only describes the relationship of the two trends. It doesn’t say anything about whether the wider availability of cannabis, or the appeal of it, is causing young adults to smoke cigarettes less.”

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    And indeed there is at least one other factor at work here. One which must certainly be taken into account, without leaping to simple conclusions.

    According to Gallup’s research, an average of 7% of US adults surveyed between 2019 and 2022 said they had vaped in the previous week, with higher rates – averaging 19% – among those aged between 18 and 29.


    If the shoe fits…


    “These data suggest that much of the decline in cigarette smoking among young adults may have been offset by vaping, indicating that young adults are still smoking products containing nicotine, but through different means,” Gallup said.

    Note that careful “may have”. In fact, the figures suggest quite clearly that the rise in vaping has indeed “offset” the drop in smoking. What can’t be said with such certainty is which effect is causing which – it could be either or neither. Or, perhaps most likely, a bit of both.

    Interestingly, the equity research firm Cowen is less circumspect than Gallup (you might say less careful) when it comes to drawing conclusions from its data.

    Noting a drop in alcohol sales in US states where cannabis is now legal, it reports: “Category interaction between cannabis and alcohol is becoming increasingly apparent. As the availability of legal cannabis expands, we continue to observe falling alcohol incidence, rising cannabis incidence and evolving risk perceptions as more consumers pick cannabis as their social lubricant of choice.”

    Which leaves the question of who falls asleep in their shoes (when socially lubricated), who wakes up with a sore head, and whether it was the booze or the weed that did it.

    – Aidan Semmens CannIntelligence staff

    Photo: Karen Arnold

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    Aidan Semmens