Monitoring trends and differences in COVID-19 case fatality rates using decomposition methods: Contributions of age structure and age-specific fatality

Christian Dudel; Tim Riffe; Enrique Acosta; Alyson A. van Raalte; Mikko Myrskyla

where the -component captures the effect of the age structure, and the -component indicates the part of the difference attributable to age-specific case-fatality. The details of the method are described in Appendix A, which also provides a step-by-step walk-through of the decomposition. Table 2 shows results for cross-country comparisons using the data from South Korea (March 26) as a reference, with countries sorted by increasing CFR. We chose South Korea as the reference because its CFR is arguably the closest match to its actual infection rate due to extensive testing and an earlier onset of the epidemic; moreover, the CFR was comparably low, and decompositions will estimate what factor leads other countries to differ from this low CFR setting, making results easy to interpret. In appendix B, we provide additional results using Germany (lowest CFR) and Italy (highest CFR) as reference countries.