Taking a chance on exposure to Covid-19
TIM HARFORD at the end of August in his Financial Times column measured the risks of going outside and the perils of the pandemic on the street. A friend of his asked: 'What I want is a survival guide for life in the age of Covid,' The man is in his sixties and has barely left home since March mostly because of the risks of travelling on the underground seem too great. Yet the man knows that his instincts may be wrong.
Tim Harford writes: 'The typical English resident, then, has a 44 in a million chance each day of being infected. In the US, the midpoint of epidemiological models suggests around 150,000 new infections a day, or 450 per million people per day, about 10 times the risk in England. In South Korea, despite the recent spike in confirmed case, the risk of infections is probably closer to 1 or 2 per million people per day.'
These averages include folk who take precautions, people who work in exposed professions and everyone inbetween. So Mr Harford says he can only guess how much his friend's risk increases if he should decide to venture outside. Yet he estimates that for his friend Covid-19 currently presents a background risk of a one in a million chance of death or lasting harm, every day. And he claims that the 'risk of death alone is one in 2m.'.
Finally Tim Harford FT article concludes: 'But simply existing in a country where the virus is uppressed but circulating is not so risky. It depends on age, gender, geography, behaviour and much else. But on average it is half a micro-mort a day-similar to taking a bath, a going skiing, or a short motorbike ride, and consideringly less risky than a scruba dive or a skydive.'
Later Tim Harford following much publicity about the risk of taking a bath, has had to admit that he was wrong and that in truth one would have take a bath for a year to run an equivalent risk, but the risk of sky diving, and scuba diving is considerably more dangerous. What really worries Mr. Harford, the host on the Radio Four program 'MORE OR LESS' dedicated to understaning statistics, is the danger of the virous surging back; and he writes: 'We cannot afford to relax just yet, because we will be walking a tightrope this autumn.'
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1 comment:
Calculations like this can be misleading unless both those making them and those attempting to make sense of them, understand clearly what question is being asked and answered, and the conditions under which the answer is valid. Using probabilities in this way to make any kind of prediction requires that cases are randomly distributed throughout the country, which we know is not the case. What matters to the individual is what is the probability that s/he will meet someone who is already infected and potentially could infect them. Whilst we can say that the probability is higher in places like Bolton at the moment, we cannot put a figure on it. The prudent thing to do would seem to be to meet as few people as possible, assume that the people that you do meet may be infectious and behave accordingly.
Incidentally on 27 August Northern Voices carried an article pointing out that the average number of cases had risen from 631 in early July to 1077 in mid-late August. The writing was on the wall then; nobody seems to have been reading it.
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