Case Fatality Ratio, Under-Reporting of Case Burden and Estimation of Excess Mortality: A Review of Challenges and Methods with Insights from COVID-19

Case fatality ratio (CFR) is a useful metric for determining severity of an epidemic in terms of mortality. This metric however needs to be used with caution. For the CFR to give an accurate estimate of the true impact of a pandemic, it must be based on the actual number of confirmed deaths and cases. However, significant under-reporting of the number of deaths and infected cases, especially during the early stages of the epidemic, makes it difficult to obtain a reliable estimate of CFR.Model based predictions based on such data can be subject to biases and could result in underestimation of the risk.It is thus imperative to ensure that the estimate of CFR accurately reflects the true nature of the epidemic.This paper discusses the problems linked with the estimation of CFR in the presence of under-reporting, and reviews some popular statistical methods which were used in the literature to estimate excess deaths due to COVID-19.