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11 May 2020updated 03 Sep 2021 1:08pm

Boris Johnson’s Covid-19 threat alert system is a parody of mathematical precision

The government uses “number theatre” to distract from the lack of clear guidance.

By Anjana Ahuja

Though we have become used to graphs, nobody expected a prime-time equation. But there it was, smuggled into the Prime Minister’s address to the nation on the evening of Sunday 10 May. 

The newly unveiled Covid-19 threat level alert system, Boris Johnson explained, would operate on a rising scale from one to five and be calculated in a very specific way. This number, according to a graphic that filled the screens of about 27 million bemused viewers, would be derived by adding R, the rate of infection, to the “number of infections”. R, which is the average number of people to whom an infected person transmits the disease (more properly called the reproduction number), has plunged during lockdown from around 3 to between 0.5 and 0.9. The number of infections is very roughly around the 220,000 mark. Clearly, adding the two together does not make a number between one and five. 

The parody of an equation evoked mathematical precision, but I suspect it was meant to convey something more modest: simply that both the reproduction number and the number of infections would be taken into account when deciding on the alert level. A threat level, whether from a virus or  terrorism, is a matter of political judgement informed by expert analysis, rather than an absolute value that can be derived from  fundamental mathematical principles. 

For me, though, it was also confirmation of the “number theatre” that is offered up regularly by the government for public consumption. That elegant phrase was coined last week by David Spiegelhalter, Winton professor of the public understanding of risk at Cambridge University,  to describe the oddly precise numbers  being thrown out daily. 

He said on the BBC’s Andrew Marr Show: “We get told lots of big numbers, precise numbers of tests being done – 96,878. Well, that’s not how many were done yesterday; it includes tests that were posted out. We’re told 31,587 people have died; no, they haven’t, it’s far more than that.” Spiegelhalter said he did not believe it was a “trustworthy communication of statistics”.

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It is almost as if the faux precision of the numbers, graphs and equations is intended to dazzle and distract from the lack of  clarity elsewhere. Number theatre is  primarily about showmanship, not science or public health. 

And yet it is the public-health guidance that really matters. We must reasonably assume that Sunday’s broadcast, accompanied by a new slogan, was a signal that the government wants us to alter our behaviour. The problem is that there is confusion about the behaviour change desired. This befuddlement was evident in the following days, with cabinet ministers being asked to clarify under what circumstances people could meet up with parents living in a different household. 

On Monday morning, Dominic Raab said that meeting both parents outside the home would be acceptable if social distancing could be maintained; by lunchtime it had been corrected to one parent only (I shall be setting a quiz for my parents; the winner is granted an awkward public stroll with the grandchildren in triangular formation).  

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Let us examine how the messaging has changed. The original Covid-19 slogan was admirably clear, if repetitive: “Stay Home, Protect the NHS, Save Lives”, in yellow and red. This has been swapped for “Stay Alert, Control the Virus, Save Lives”, in yellow and green. Is the switch from red to green a subliminal call to action? Do I no longer have to stay home or protect the NHS?

Make of it what you will, because Johnson is “actively encouraging” people to return to work. Caveats, though, litter his exhortations: go back to work if you cannot work from home, but avoid public transport. Social distancing should be maintained where possible. 

For millions of commuters, public transport is the only route to work. So, if I can only get to work via the Tube or train, can I reasonably refuse to turn up? Can I also deny my labour if I am not a key worker and therefore not entitled to send my children to school? If I do use public transport and need a face covering as now recommended, should my employer provide a mask? What if social distancing is not maintained in  the workplace? 

Professor Susan Michie, director of the Centre for Behaviour Change at University College London, tweeted on 10 May that her “understanding is that returning to work is predicated on a guaranteed safe working environment – and presumably not having children to look after or vulnerable family members”. That a behavioural expert on the government’s scientific advisory group should need to “presume” what Johnson’s address meant was telling. Meanwhile, Scotland, Wales and Northern Ireland are sticking with the “stay at home” message, for fear of causing a spike in infections. 

This is where we truly need the detail: how do we restart the economy without restarting chains of transmission? How do I adhere to the new slogan? How can I personally “control” the virus? Isn’t that, in any case, the function of government, through testing, tracing and isolating? Ministers, dismissive of the accusation that the new rules are vague, despite struggling to articulate them, have appealed to people to use their own judgement. It looks suspiciously like setting us all up to take the blame when the second wave of infections comes, as it almost certainly will.

Although rough numbers can be handy for gauging progress, evidence-informed guidance is more useful than knowing whether 96,878 or 96,879 tests have been carried out. It is time to bring the curtain down on number theatre. 

Anjana Ahuja is a contributing writer on science for the Financial Times

This article appears in the 13 May 2020 issue of the New Statesman, Land of confusion