A reader writes:

With all the uncertainty about how many cases there are and limited testing, I think the best approach is the same one you use with crime statistics:

robberies can fluctuate depending on how many are reported, but you can’t ignore a body.

In other words, look at the deaths. Bodies can’t be ignored and are probably much much more likely to be tested.

Then you can extrapolate, roughly, using estimates of the fatality rate.

For example, Washington state (where I live), has 31 COVID-19 deaths to date. Taking a rough estimate of a 1% fatality rate, that gives you an estimate of 3000 cases in WA (much higher than the ~450 confirmed cases). Or look at Italy – they have over 1000 deaths. Their fatality rate is probably higher due to the health system breaking down, so say rough estimate of 2%. That gives 50,000 cases – again, much higher than the ~15,000 confirmed cases.

I think people are systematically underestimating the extent and I’m worried.

If Italy has 50,000 cases, then (with doubling time of 5 days) they will have 800K cases in 20 days. Their quarantine measures should slow the doubling time, though.