Last week brought lots of headlines about a new study claiming moderate drinking doesn’t really provide health benefits.
The new paper claims to better adjust for sick-quitter confounds by using lifetime never-drinkers as comparison group, but this is hardly a new technique: Rimm and Moats 2007 notably restricted their sample to healthy people who exercised and who had good diets – they found strong protective effects for moderate drinkers as compared to abstainers, even if the NZ MoH wants to pretend otherwise.
Statistician David Spiegelhalter walks through the latest evidence. Basically, there was no power to their test because they had too few never-drinkers in their sample, so nothing came up as statistically significant. He concludes:
So a more appropriate headline would have been “Study supports a moderate protective effect of alcohol“.In summary, the study is grossly underpowered to convincingly prove a plausible protection, and they have committed the cardinal sin of saying that non-significance is the same as ‘no effect’ in a study lacking sufficient events, in this case, deaths in non-drinkers. Maybe epidemiological studies should include power calculations, which make sure there is a reasonable chance of detecting a plausible effect, and which became standard in clinical trials after too-small studies were being used to claim that drugs did not work.This is a poor use of statistics, and I am surprised it got past the referees and into the journal. A recent analysis showed that exaggerated health stories in the media were not generally the fault of the journalists, but the press releases they had been fed. Rather ironically, the analysis appeared in the British Medical Journal.
And see Snowdon, here.
How long until New Zealand’s MoH starts citing this as further evidence against the health benefits of moderate drinking?
The NZ Cancer Society has been pushing a “no safe level” message around alcohol and cancer risk. As best I understand the literature, cancer risk is always increasing in alcohol consumption. But unless you have a strong family history of cancer as opposed to other things, it ought to be all-source mortality you look to for medical risks. The protective effects of moderate consumption are well established. But there does seem to be some determination to downplay those overall effects while emphasizing the disorders worsened by alcohol.