Friday, 23 October 2020

Garbage in, garbage out - food advertising edition

After the year we've had, I suspect a lot of people have had a bellyful of models from 'public health' which reflect nothing more than the assumptions of their authors (see yesterday's post, for example). But let's go once more in the breach.

Ban on junk food ads before the 9pm watershed could stop 160,000 children becoming overweight or obese, study claims

The UK government's ban on junk food ads before the 9pm watershed will stop 160,000 children becoming overweight or obese, according to experts. 

Children would avoid eating about nine calories a day on average, which would reduce childhood obesity figures by nearly 5 per cent, they claim.

Who is claiming this? Step forward Oliver Mytton, who modelled the sugar tax, Emma Boyland, a long time campaigner for food advertising bans, and various colleagues. Not least among them is Russell Viner who has also been campaigning for an ad ban for years and who, in 2018, got £5 million of taxpayers money for an 'obesity policy research unit'

The new model is based on results from a study by none other than Russell Viner which claimed that watching 'junk food' advertising for 4.4 minutes makes kids eat 60 more calories than they otherwise would. The government's impact assessment for the ad ban is also based on this factoid.

Is it a reliable figure? Reader, it is not. It was arrived at by mixing together a bunch of sketchy and contradictory studies from unrealistic experiments in which (mostly young) children were given unlimited free food and no parental control, as I explained last year. 

If one looks at the studies themselves, rather than rely on Viner et al's interpretation, it becomes clear that the 60 calorie claim is based on some very mixed evidence, dominated by a series of studies from one research group whose members have strong feelings about the subject

The whole thing is a fantasy. As with so much in the modern 'public health' racket, it is a model within a model. The sunshine of reality is never allowed to creep through the curtains.

Viner and colleagues were not in any way deterred from their conclusion by the observable fact that children's 'exposure' to 'junk food' on TV has fallen by 70 per cent in the last 15 years without any apparent impact on calorie consumption or obesity. 

Nor do Viner and his new colleagues let real world evidence distract them in their new study. They begin by admitting that "little is known about the impact of advertising on childhood obesity and overweight". So much for evidence-based policy. Alas, the reader won't know any more by the end of it, because it's all fantasy modelling. They take the fictitious 60 calorie figure and extrapolate that kids will consume 9.1 fewer calories a day if they see one and a half fewer 'junk food' adverts per day under a watershed ban.

Further extrapolations lead them to believe that consuming 9.1 fewer calories a day will lead to childhood obesity falling by 4.6% which sounds implausible but I can't be bothered to look at their methodology because, frankly, what's the point? Interestingly, they use the international definition of childhood obesity rather than the totally unscientific UK definition, meaning that a 4.6% decline in child obesity will mean the rate falling from 8.8% to 8.4%. Add in the number of kids who are 'overweight' (none of whom are fat, in reality) and you get the 160,000 children mentioned in the headline above. 
As if that were not enough guesswork, they then make wild extrapolations about the intangible monetary benefits that will be accrued over the course of these children's entire lifetime based on the assumption that none of them will ever become obese (£7.4 billion apparently). 

They admit that these 'benefits' will be reduced by as much as two-thirds if the ads are shown after 9pm instead (which they will), but that only gives them an opportunity to lobby for the inevitable next step of a round-the-clock ban which seems to be the authors' intention.
Or rather it is their intention now that the government has already capitulated on the 9pm ban. The journal received their manuscript last December when the ban was far from a done deal. Like many models in 'public health', it seems designed to act as a political spur rather than provide scientific illumination. They say that "the modelled scenarios are best understood as explorations of what the policy could achieve rather than predictions of what will happen". Where have I heard that before?   
Nevertheless, they conclude by asserting that...

Our study demonstrates that less-healthy food advertising on television in the UK is making a meaningful contribution to childhood overweight and obesity

No, it really doesn't.

No comments: