I find the whole thing confusing.
How do we know what R is unless you have full testing?
The official line is as followsIndividual modelling groups use a range of data to estimate R including:
- epidemiological data such as hospital admissions, ICU admissions and deaths – it generally takes 2 to 3 weeks for changes in R to be reflected in these data sources, due to the time between infection and needing hospital care
- contact pattern surveys that gather information on behaviour – these can be quicker (with a lag of around a week) but can be open to bias as they often rely on self-reported behaviour
- household infection surveys where blood samples and swabs are performed on individuals which can provide estimates of how many people are infected – longitudinal surveys (which sample the same people repeatedly) allow a direct estimate of the infection rates
Different modelling groups use different data sources to estimate R using complex mathematical models that simulate the spread of infections. Some may even use all these sources of information to adjust their models to better reflect the real-world situation. There is uncertainty in all these data sources, which is why R estimates can vary between different models, and why we do not rely on one model; evidence is considered, discussed and R is presented as a range.
Who estimates R?
R is estimated by a range of independent modelling groups based in universities and Public Health England (PHE). The modelling groups present their individual R estimates to the Science Pandemic Influenza Modelling group (SPI-M) - a subgroup of SAGE - for discussion. Attendees compare the different estimates of R and SPI- M collectively agrees a range which R is very likely to be within.
Now that's as clear as mud to me.
We are guessing ( estimating) based on data that 2/3 weeks old from various sources.