Next up: the snack tax

With crushing inevitability, the first UK modelling study promoting a tax on food has been published in the BMJ. And guess what? The researchers reckon that it will work. In fact, they think it will work even better than taxes on sugary drinks - which have never worked anywhere. An accompanying editorial in the journal gives the policy its blessing.

The BMJ's modelling study promoting sugary drink taxes has now been largely forgotten, despite being highly influential at the time, but it promised a fall in obesity of 1.3 per percentage points. Today's study predicts a decline of 2.7 percentage points.

One of the authors told the Guardian:

Dr Pauline Scheelbeek from the London School of Hygiene and Tropical Medicine, the lead author of the study, said a snack tax could cut obesity in the UK population from about 28% to about 25%. “That is, on a population level, a huge impact,” she said.

'Public health' has a wretched record of health-economic modelling. It repeatedly promises outcomes that are not delivered and then uses retrospective modelling to make it look as if they were (eg. Mexican sugar tax, English smoking ban).

Models are only as good as the assumptions fed into them by the researchers. If the researchers tell the model that the policy will work, all the model can do is estimate how well it will work to the nearest decimal point.

The modellers of this new study don't look at how much their tax on confectionery, biscuits, and cake will cost consumers, but it would clearly run into many millions of pounds and hit people on low incomes the hardest. The researchers brush this off with the usual rhetoric about the health of the poor benefiting the most, despite there being no evidence that this is how sin taxes operate in practice.

I would bet a pound to a pork scratching that if the tax proposed has any effect on obesity it will be far, far smaller than is reported in this model. But let's imagine that it is correct. Let's imagine that it really does reduce the adult obesity rate from 28% to 25%. Do you think the nanny statists will congratulate themselves on a job well done and leave the public alone? Or do you think they will devise new ways to tax and control us?

You don't need a wonky predictive model to work that one out.