November 12, 2016

Fizzy headlines

Herald (Daily Mail) headline: How just one can of fizzy drink a day raises the risk of developing type 2 diabetes by 50pc. Here’s the research abstract

  1. The research was about pre-diabetes, or ‘elevated fasting glucose/impaired glucose tolerance’ as it used to be called, not diabetes.  They aren’t remotely the same thing. According to this other research, so-called pre-diabetes has about a 5-10% chance per year of turning into diabetes and about the same chance of just going away.  About half the people in the study  developed pre-diabetes over a seven-year period, even among those who didn’t drink any soft drinks.
  2. The researchers distinguished sugar-sweetened and diet drinks (they saw no suggestion of a risk increase for diet drinks) but did not distinguish fizzy from non-fizzy sugar-sweetened drinks. So the headline divides drinks up in a completely different way from the research. This wasn’t ‘fizzy drink’ research.
  3. The research paper reports multiple estimates of the risk increase. Some models said nearly 50%, but some said about 25%.
  4. There’s a lot of uncertainty even in the purely mathematical sense: the model that says nearly 50% increase came with an uncertainty interval that goes down to 16%, and the one that says 25% has an uncertainty interval going all the way down to zero.

The research itself is perfectly reasonable, providing a bit more evidence on the risks of high-sugar diet (disclaimer: I know a few of the researchers). Even the story isn’t too bad, but the headline is basically completely wrong.

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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. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »