I've copied this for NewJudge as it gives a summary of how R0 is being calculated (estimated). It was written last week and I think more use is being made of the sampling exercise.
R0- How do we measure it?
There are lots of different ways of calculating R. Scientists have been looking at the genome of the virus to see how it changes as it infects new people. They can also look to death and hospitalisation figures to get a sense of how many people have contracted the disease. The problem is that most of these methods involve looking into the past to some degree. People who unfortunately die from coronavirus will have been infected weeks before, so using that data to calculate R can only tell you how widely the disease was infecting people several weeks ago.
To get a more up-to-date sense of the coronavirus R number, the UK is starting to test random samples of the population to see how many of them have the disease. This test, which will be carried out monthly, will involve at least 25,000 people who will be tested to see if they’re currently ill with the virus. This should help the government track the changes in R over time and see if the infection rate is rising or falling.
What is R right now?
At the April 30 press conference, the UK’s chief scientific officer Patrick Vallence said that the UK’s R0 was between 0.6 and 0.9 while the figure in London was between 0.5 and 0.7. It’s worth noting that the precise R will vary from location to location, but these numbers suggest that the enforced lockdown is having the desired effect of forcing the transmission of the virus down.
What isn’t clear, however, is how the R will change if and when the government chooses to relax its social distancing measures and it’s this change that advisors will be keeping a very close eye on to see if the UK is keeping a second peak at bay. It’s worth noting that the R won’t be the only number worth keeping an eye on. Also critical is that the UK doesn’t exceed its critical care bed capacity, and that the NHS has enough spare capacity to resume normal treatments as this too will have a big impact on the overall mortality of the coronavirus pandemic.