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

The total difference between two CFRs as well as both and can be negative. The formulas for the relative contributions take this into account by using absolute values. If the total difference is positive and either or are negative, it means that the corresponding part of the difference actually reduces the difference between CFRs. For instance, when comparing the CFR for one country at two points in time, the total difference could be 0.03; i.e., the CFR increased by three percentage points. If in this case would be negative, say −0.01, it would mean that the age distribution of cases over time became more favorable. would be 0.04 in this scenario, and without changes in the age distribution of infections as captured through , the difference between CFRs would even have increased by four percentage points.