Is the R number a flawed measure?

Boris Johnson’s address on Sunday was always going to be challenging. The effects of Covid-19 – in terms of its horrific death toll and the drastic measures we’ve taken to prevent more loss of life – meant it was one the biggest and most important political statements in living memory.

But what was also required was transparency and the explanation of very difficult scientific and medical concepts. In his statement, Boris Johnson drew attention to the R value, which he said was key to the changing lockdown measures over the coming weeks. If it crept above 1 this meant Covid-19 was spreading and the lockdown measures would remain in place, and if it fell below 1 it was an indication we were beating the virus. The problem is the R value is essentially guesswork.

As you would no doubt expect, science and its concepts are rarely straightforward or clear-cut. A classic example of this is social distancing.