"The report overflows with thunderous threats about the impending lung cancer epidemic from smoking cannabis. I guess pretty soon we will be seeing science on ‘passive smoke’ from cannabis causing everything from baldness to saggy breasts in innocent bystanders. Can we have a workplace ban on smoking cannabis, please? How about throwing some more money down the anti-cannabis rathole?"
We link at the bottom of this page to columnist Søren Højbjerg’s commentary on a recent study purporting a danger of lung cancer from marijuana use. A link to the original study itself ("Cannabis use and risk of lung cancer") is included within his column. Rhetoric about "secondhand pot smoke" may indeed ensue in the future although it’s worth noting incidentally that this study (see third paragraph of its Results section) finds no relationship whatever between lung cancer and environmental tobacco smoke. Of course no studies really do but Healthist "researchers" never let that dampen propaganda.
The methodological absurdity of this study will amuse readers. Its touted result is a 570% increased risk of lung cancer from smoking a joint a day for more than ten and one half years. However readers may also note (fourth paragraph of Results section) another buried observation: "While cannabis smoking was not associated with a significantly increased risk of lung cancer … those with the highest tertile of use … had a significantly increased risk." What, you ask, there is a 570% increase, but also, cannabis smoking has no risk?
For the answer look at study Table Two. The 5.7 relative risk (570% increase) was derived by segmenting just 14 cases and 4 controls. The confidence interval is anywhere from 1.5 to 21.6. This result is absolutely meaningless. Take into consideration the whole marijuana-smoking group, and the "risk" disappears (a statistically insignificant 1.2), while for those in the first two categories of marijuana smokers, the (likewise statistically insignificant) relative risk results are a reduction of risk, by at least half, or to less than a third, as for persons who never smoked pot.
The touted 570% is for generating a scare and more grant money for researchers. The study size, even including all as opposed to a focus on pretentious and ludicrous segmenting, does not and could never really suggest anything practically significant, even if that were the genuine aim. This "study" is pure silliness. Most such studies are.
The river of foolishness runs deep here. Did you also note the odd usage level standard of ten and one half years? They could have made it anything. Why not ten? Why not five or twenty? Well, then, also note (study Table One) the still odder cut-off for lighter use of marijuana: one and thirty-nine one hundredths of a year. This is an example of a common, intentionally obscured, element of "cherry-picking."
The segments were contrived to place interviewees into an array of categories for which the "relative risk" would at least appear to head in the right direction (higher relative risk number with higher pot use) and also to compute to a (barely) "statistically significant" result at the end. Yes odd, yes silly, more and more the closer you read. Very typical too. Søren Højbjerg dissects the ideological basis of such silliness in his latest column, for which, click the link below.