Dr Waqar Rashid Dr Waqar Rashid

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. The 2m social distancing rule in the UK is based on SAGE’s opinion, the WHO (not an organisation, admittedly, which has covered itself in glory during this pandemic) recommends 1m and most of the medical evidence suggests around 1m is effective to stop the spread of the disease. Yet I have even seen it recommended that people stay up to 6m apart. How society operates with a 6m figure is anyone’s guess.

This illustrates scientific uncertainty but also the pitfalls of trying to translate medical evidence into policy and real life. When governments communicate social distancing measures, there are no caveats: only a distance of 2m will save lives. But when you speak with such certainty, it becomes very hard to reverse policies when then may cause harm. This is also true of the R value.

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