Economical with the truth


We read today that ‘Britons are increasingly under-reporting their daily calorie consumption’ (The Guardian, Monday 8th August 2016), a news item carried widely by the national media. It is based on a report called ‘Counting Calories – How under-reporting can explain the apparent fall in calorie intake’, which is available here:

This report was produced by a unit called The Behavioural Insights Team (BIT), a quango hived off from 10 Downing Street, the origins of which stem from the adoption by our Government of ‘nudge’ policies a few years ago.

It is only necessary to read the contents page to realise that this report is a pretty thorough piece of work, and one on which I will probably have more to say when I have absorbed it in detail.

Flicking to the end has already produced a gem of a tailpiece written by the Government Statistical Service (GSS) – of which BIT is not part – and which has clearly been embarrassed by the report, producing as it does much of the data dogged by under-reporting. The GSS admits that ‘it has long been recognised that under-reporting in dietary surveys means that official estimates of calorie consumption are likely to be underestimates.’  ‘New technologies … have the potential to deliver significant improvements. These are being considered but are not ready to be introduced in the near future.’

But carping at the Civil Service is not the aim of this blog. As a career survey statistician I am well aware that it is easier to identify such issues than to fix them. Britons (like every other people) are indeed economical with the truth about we swallow, and for a great many reasons, not all involving subterfuge.

Rather, today’s subject is about the faint praise above for the BIT report, when I said that it is ‘a pretty thorough piece of work’. Not actually thorough, because one particular word is not used at all in the report; that word is alcohol. Its only mention is in the title of one of the references, and no discussion is made of this.

There is a reason that I think this is a noteworthy omission. Although BIT doesn’t mention it, under-reporting of alcohol intake is also a major issue, and one which has been known about and studied for decades. It is believed that most published data under-estimate intake by about 30%-50% – about the same shortfall as BIT says applies to total calories.

You might think that under-reporting of alcohol intake is a significant factor in the overall under-reporting of calorie intake, but that isn’t really so. Anyone drinking the 14 ‘allowed’ units of alcohol per week is taking in about 900 calories this way. Since BIT now says that we are absorbing about 3,000 calories per day in total, then alcohol represents on average just 4% of this. So its influence on BITs estimates of bias must be modest. Maybe this is the reason that BIT doesn’t think alcohol is worth mentioning.

But I think they should have done, and my reason is that the Government has social policies directed specifically as alcohol – such as the drinking guidelines. Moreover, the bias in data on alcohol intake seems to have been ignored in setting these guidelines and thus jeopardises their basis in fact. I will go into this more fully at another time, but it is easy to illustrate. If the risk of certain illnesses begins to rise worryingly at an intake of 14 units per week, remember that this is a claimed 14 units. Given the under-reporting, the true level is probably around 20-28 units per week (20 less 30% underclaim gives a reported 14; 28 less a 50% underclaim also gives 14). So the rise in risk is actually occurring at much higher intake levels; ergo, alcohol is not as dangerous as it’s made out to be!

This is a simplistic calculation but it is not wrong. I made a similar point in a different forum soon after the new guidelines were announced, which you can read here:

See the reply by Trevor.

Returning to the BIT report, maybe we should be grateful to the authors not to have drawn attention to alcohol intake yet again. If you know anyone in government, don’t recommend this blog to them!

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