A guide to R — the pandemic’s misunderstood metric - Nature

What the reproduction number can and can’t tell us about managing COVID-19.

R, the average number of people each person with a disease goes on to infect.

In this pandemic, R has leapt from the pages of academic journals into regular discussions by politicians and newspapers, framed as a number that will shape everyone’s lives. As Germany’s chancellor, Angela Merkel, explained in a widely viewed video this April, an R above one means an outbreak is growing, and below one means that it is shrinking. In many countries, it is publicly reported every week...