5 ms·

I don’t understand why you couldn’t use the average rate of infection to compute this.

• makomk 6y ago
  Suppose that cases are going down almost everywhere and you compute the average and calculate R from that, getting a nice reassuring number below 1 - but there's some part of society, somewhere, where cases are still increasing exponentially. Just a small fraction of cases initially. Over time, the number of cases in the parts of society where Covid is under control decrease whilst the cases in the parts where it isn't increase, until inevitably the rate at which cases grow is completely dominated by the bits where Covid is out of control, even when those started off so small as to have almost no effect on the overall average. That's why you can't just rely on the average. (In fact, I'm pretty sure the fraction of cases which are caused by the parts where Covid is still under control should decrease exponentially.) Also, remember that the effective rate of reproduction can easily vary by huge amounts between different parts of society, for example if some age groups are almost completely vaccinated and others are almost completely unvaccinated.