Since talk about R0's are going viral, I'll mention why I think the R0 is an interesting philosophy of science topic.
While R0 is sometimes treated like a basic scientific constant (like Planck's constant or something), it's way different.
While R0 is sometimes treated like a basic scientific constant (like Planck's constant or something), it's way different.
R0 is an important number in epidemology that measures infectiousness. It's something like "how many new cases can one infected person cause."
It shows up in many epidemiological models, like the classic Susceptible-Infectious-Recovered (SIR) model.
It shows up in many epidemiological models, like the classic Susceptible-Infectious-Recovered (SIR) model.
At first glance, it seems like R0 is a theoretical concept which attaches to a virus. ("The current coronavirus in Wuhan has an R0 of....") Or perhaps more carefully, it attaches to a virus-host system. But R0 is actually way weirder than that.
R0 depends on all sorts of things. With many diseases it changes with the seasons, because features of the outside environment can affect how easily a disease is transmitted.
What's more, R0 depends on all sorts of social factors like hygiene practices, how much people interact, whether they wear face masks, and whether the government is actively intervening or not.
As we're seeing now, estimates of R0 numbers influence public reaction and governmental intervention. Early estimates of the Wuhan outbreak had high R0 estimates, and so the government intervened. That intervention may well lower the R0.
Scientific estimates of R0 actually CHANGE the R0, by changing how people behave and how governments react.
So, R0 is far from the classic objective fact about the world (like the gravitational constant). Instead, it's far more complicated. And, far more interesting.
