Case-fatality ratio

After omitting countries with <50 total observed cases, we computed a crude case-fatality ratio (CFR) for each country by dividing observed deaths by cases. For countries with available age-specific data, we computed: (i) an age-standardised CFR, derived as above by applying countries’ age-specific crude CFRs to the world's population structure; and (ii) an incidence-standardised CFR, derived by applying each country's age-specific CFRs to the observed age-specific caseload in South Korea, selected as a reference due to this country's reportedly high coverage of case detection (i.e., relatively low selection bias affecting the profile of observed cases) and standard of care (Report on the epidemiological features of coronavirus disease 2019 covid-19 outbreak in the republic of Korea from January 19 to March 2, 2020, 2020). The chosen standardisation method aims to (i) account for age differences in infection-fatality ratios while (ii) reducing bias due to incomplete testing; neither, however, accounts for the effect of age structure on incidence or entirely removes confounding.