COVID-19 and the difficulty of inferring epidemiological parameters from clinical data

[...]seeing how to usefully incorporate the six positive cases from this sample is difficult. Case mortality data from China provide an upper bound for the IFR, and with extra assumptions these data also supply information on how the IFR varies with age. Because prevalence is unknown, the data contain no information for estimating the absolute IFR magnitude. Because of extensive testing, the outbreak on the Diamond Princess, the quarantined cruise liner (used only for validation by Verity and colleagues) supplies data on infections and symptomatic cases, with fewer ascertainment problems.