Denominators yet again
Tony Cooper, in a Stat of the Week nomination, point us to the Herald’s headline
“Men over 50 nation’s biggest drinkers”
When you look at the body of the text, though, the data only say that men over 50, in aggregate, drank more than the other subgroups of the population. That’s somewhat relevant if you are planning a sales campaign, in which case the Roy Morgan report might be useful. It doesn’t tell you which group are the biggest drinkers, because that depends on per-person alcohol consumption.
As two of the experts actually quoted in the story said, men over 50 accounted for the largest chunk of the booze because there are a lot of men over 50, not because they are the heaviest drinkers. A little simple arithmetic shows that, per person, men over 50 drank less than men 35-50, and less than men 25-34. Not doing the arithmetic is one thing, but it really doesn’t look good when the headline also directly contradicts what your sources are quoted as telling you.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. See all posts by Thomas Lumley »