Q: How do you make your #COVID19 situation look less scary, without actually combating the disease?
A: Fiddle with the data.
That's what's just happened here in England. Test & Trace have quietly changed their data, suddenly changing our picture of the severity of the disease

The starting point is to note that perhaps the best measure (admittedly of a bad bunch) when it comes to overall case data, is to work out the number of positive cases as a percentage of tests taken. Here is how that chart looked for England as of last week. Scary, right?

Given cases are rising pretty quickly, it looked v much as if by this week England's positivity rate would have been above France/Spain. So here's what the statisticians have done: changed their definition for the total number of tests. Footnote here: https://www.gov.uk/government/publications/nhs-test-and-trace-statistics-england-methodology/nhs-test-and-trace-statistics-england-methodology

Now this might be a better way to count overall tests. Which is good. But first off, this is an obscure footnote, not even included in the Test & Trace report itself, but in a link. Why be so surreptitious? Second, it has major implications and completely changes the picture:

As a result of an obscure statistical switch no-one was supposed to notice, the #COVID19 positivity rate in England has gone from looking like it's worse than France and Spain to looking better. Look at the red lines here. Which are we supposed to believe?

As I say, this is plausibly a better way of measuring it. So why do it so surreptitiously and with precious little context/framing? Data is central to understanding #COVID19. Quietly messing with the data further undermines confidence in it - and the handling of the pandemic.