This post ranks countries and regions by the ratio of deaths to confirmed cases. This is a good indicator of testing efficiency. Assuming that the ultimate death rates are similar across countries and regions then a higher ratio at this point in time indicates that the number of confirmed cases is too low compared to the actual number of infections in the community.
The Diamond Princess is used as a benchmark as it is a population that was 100% tested and hence the ultimate death rate on the cruise ship is a good indication of what will be the case in the broader community.
The ratio calculation uses the confirmed cases from 10 days prior given that there is a lag between a case being confirmed and deaths.
The ratios for all countries with 500 hundred current confirmed cases and over 100 confirmed cases 10 days ago are included.
The OECD rankings are presented below to compare countries with broadly similar health systems.
The testing performance of different US states is compared below.