Carl Heneghan

How is the Vallance Covid projection working out?

Picture by Pippa Fowles/No. 10 Downing Street

Prediction, projection, illustration — call it what you wish, but when you make a statement about what’s going to happen next, people are going to assess whether you’re correct or not. Sir Patrick Vallance, the Chief Scientific Adviser, said last week: 

At the moment we think that the epidemic is doubling roughly every seven days…If, and that’s quite a big if, but if that continues unabated, and this grows, doubling every seven days… if that continued, you would end up with something like 50,000 cases in the middle of October per day.

Making projections is fraught with danger, but there are ways to caveat such statements that allow better understanding. For instance, it is looking gloomy today and the weather forecast says there is a 50 per cent chance of rain. Providing a probability estimate gives us a much better understanding of the likelihood of an event occurring, and it allows us to prepare; we think we’ll take an umbrella.

Written by
Carl Heneghan
Carl Heneghan is professor of evidence-based medicine at the University of Oxford and director of the Centre for Evidence-Based Medicine

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