What we found
In establishing an RADIR value based on cases we were helped, during the period that we evaluated, by the UK National Health Service (NHS) in England operating on a testing strategy to confirm a diagnosis in symptomatic individuals. With a third of tests in symptomatic individuals being positive over the period studied, we made the assumption that positive tests reflected a small consistent more severe proportion of the total infected cohort.
We showed an independent relation over time between our calculated RADIR value and the number of cases identified as definitely positive in the population. We then inferred by extrapolation using a linear regression model that by late April, 26.8% of the total population were possibly infected (1). We did not seek to establish an absolute proportion of the total infected number for the population.