Was the two-metre rule one big lie? By covering up complexity with nice round numbers, public health officials treat us like children

Of course, the virus doesn’t follow rules. If somebody is infectious, there is no hard limit beyond which you are safe. And, since people can be infectious before showing any symptoms, anyone represents at least a theoretical risk of infection. We are looking at degrees of risk, and what measures we’re willing to take to reduce them. Outdoors is safer than indoors. Wearing a mask is safer than not. Facing the same way and talking like spies meeting on a park bench is safer than face to face. And all this is provisional, as we’re not putting patients in labs and letting them breathe on volunteers to find out.

It could just be that the British Government wanted to wait until the disease was less prevalent before letting us get a little closer. Or it could be the latest in a long history of telling us, not what the science says, but what the public health officials think we need to be told.

Take “5 a Day”, the guideline that tells us all to eat five portions of fruit and vegetables every day (potatoes don’t count, despite being so rich in Vitamin C that their introduction to Britain ended endemic scurvy). That has a number in, so surely it must be based on scientific research? Indeed, the NHS “Why  5 A Day?” page says the campaign is based on WHO advice to eat 400g of fruit and vegetables to lower the risk of heart disease, stroke and cancer.

There is research linking more fruit and vegetables to lower risks of some diseases, but that’s not the origin of the campaign. In 1980s California, the state’s Department of Health Services found a happy harmony between the desire to improve public health through diet, and the economic benefit to the region’s farmers from increased sales. In the American Journal of Preventive Medicine, the Department’s then Director, Ken Kizer, summarised its success:

“The 5 a Day-for Better Health! Campaign had several distinctive features, including its simple, positive, behavior-specific message to eat 5 servings of fruits and vegetables every day as part of a low-fat, high fiber diet; its use of mass media; its partnership between the state health department and the produce and supermarket industries; and its extensive use of point-of-purchase messages.”

Professor Tim Lang was advising the UK government in the late 1990s when he was told of the US campaign and felt “we needed something”. Tony Blair’s Labour government was looking for specific policy targets, and five was “a nice round number”. The scientific precision of 400g was retrofitted later to give the “simple, positive, behaviour-specific message” more scientific authority.

Or take government guidelines for how much alcohol we should drink, revised in 2016 to “You are safest not to drink regularly more than 14 units per week.” This was cut down from the old guidelines, which were 14 units for women and 21 for men, recognising the differences in average physiology. They in turn were revised downwards in 1984 from 56 units per week, almost a bottle of wine per day. Our parents were made of sterner stuff.

But the new guidelines are based on better science, right?

Well, it depends what you mean by science. Like most public health questions, it would be unethical to apply randomised controlled trial methods to habits that you suspect are unhealthy. Nobody assigned human adults randomly to drink nearly a bottle of wine a day or no alcohol at all, and recorded their time and cause of death. Health advice is based on a mixture of ‘ecological’ observation (real humans drinking in the wild and then reporting their intake) and mathematical modelling.

The new guidelines took an extreme position on the protective effects of small amounts of alcohol (around a unit a day) against cardiovascular diseases, for which there is robust evidence. Light drinkers are around 20% less likely to die of anything in a given period than teetotallers, even excluding people who have stopped drinking because they’re ill.

Arguing that deaths from cardiovascular disease have fallen significantly, the Chief Medical Officers argued that this made the protective effect less important, and that it was only significant in women over 55. They may have based this on a paper published in the BMJ claiming that such benefits were limited to women over 65, a claim that the statistician Professor David Spiegelhalter described as misleading, commenting that “a more appropriate headline would have been ‘Study supports a moderate protective effect of alcohol’ … This is a poor use of statistics, and I am surprised it got past the referees and into the journal.”

The new, lower drinking guidelines are not a change in public message that reflects a change in scientific research. The research has been selected, or even commissioned, to justify new, lower guidelines. A more honest public health message would be: “Depending on who you are, a drink a day is probably good for you, and every subsequent drink increases your risk of illness and death”. But that would muddy the “simple, positive, behavior-specific message”.

Public health campaigns are, by nature, broad brush and aimed at mass populations. Most of us want rules of thumb, not scientific papers, when we’re weighing up what to eat, drink or smoke, whether to go for a run, how close to stand in the supermarket queue. We understand that advice is to be taken in context, not as a protective spell that will guard us from all harm.

In a pandemic, as new understanding emerges by the day, clarity is even more important. As early as February, scientific advice to the government about how to handle the Covid-19 pandemic included the importance of being clear and definitive, coherent and consistent, not only to improve compliance with helpful actions, but to discourage pointless or counterproductive ones.

But this is no excuse for dishonesty about the basis for official advice or rules. Where the scientific basis for policies was uncertain, it would have been far better to say that the science was uncertain, but the government had made a decision for these reasons: erring on the side of caution until more was known, or recognising that human life is about more than medical health.

When the WHO switched its advice to one metre, what was the rationale for sticking with two? Fear of looking indecisive? Lack of faith in British people to know what a metre looks like? In mid-March, the UK’s scientific advisory group, SAGE, was invoking behavioural science to argue that the public is mostly rational and altruistic in a crisis:

“The behavioural science points to openly explaining to the public where the greatest risks lie and what individuals can do to reduce their own risk … Greater transparency will help people understand personal risk and enable personal agency, send useful signals about risk in general and build public trust. Citizens should be treated as rational actors, capable of taking decisions for themselves and managing personal risk.”

Of all the expert advice given to the government, it’s a pity this paragraph has been so often ignored.

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Timandra Harkness presents the BBC Radio 4 series, FutureProofing and How To Disagree. Her book, Big Data: Does Size Matter? is published by Bloomsbury Sigma.

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