THREAD:
Washington state is a good example of the importance of accounting for the number of tests when reporting COVID-19 case counts. Remember I mentioned a couple of days ago how their number of cases in WA had begun to stabilize? Well, guess what happened...
Washington state is a good example of the importance of accounting for the number of tests when reporting COVID-19 case counts. Remember I mentioned a couple of days ago how their number of cases in WA had begun to stabilize? Well, guess what happened...
Today, they reported 189 positives, along with 175 yesterday, as compared with an average of 106 positives per day in the 7 days before that. So, not great on the surface... new cases increased by 70%! But you also have to look at the number of tests.
covidtracking.com/data/state/was…
covidtracking.com/data/state/was…
Washington conducted 3,607 tests today and 2,976 yesterday. By comparison, they'd conducted an average of 1,670 tests in the 7 days before that. So they've increased testing capacity by 97% over their baseline. Meanwhile, detected cases have increased, but by "only" 70%.
Looked at another way: Today, 5.2% of Washington's tests came up with a positive result. Yesterday, 5.9% did. In the 7 days before that, 6.4% of them did. So, there *is* a bit of progress after all. Their number of new positives *as a share of new tests* is slightly declining.
For the time being, 1) the large (perhaps very large) majority of coronavirus positives are undetected and 2) test capacity is ramping up at extremely fast rates, far faster than coronavirus itself would spread even under worst-case assumptions.
So long as those two things hold, the rate of increase in the number of *detected* cases is primarily a function of the rate of increase in the number of *tests* and does not tell us that much about how fast the actual *infection* is spreading.
