Estimating Missing Data

Johannes Ernst uses a neat trick to estimate the missing data:

To compare, Santa Clara County (about 1.8 million people) today reports on its website 79 Coronavirus cases, of which 36 are hospitalized. Accounting for the disaster that is testing in the US, other countries have about 10% of known cases hospitalized, so that would lead to about 360 known cases if testing had been done properly.