from The Atlantic:

Wuhan’s coronavirus outbreak sounds scary. But information about its contagiousness requires context.

One oft-cited number in particular helps experts understand how quickly an outbreak could spread. It’s also easily misread.

R0 (pronounced R-nought) describes the average number of people a single affected individual will infect. Researchers estimate that this coronavirus has an R0 of about 2 to 3.

But plenty of external factors—such as how quickly cases are treated—can affect transmission rates. “A bigger R0 doesn’t necessarily mean a worse disease,” our staff writer Ed Yong writes.

One example: the R0 of measles? A whopping 12 to 16.