In the face of the pandemic, are all equal? On the suitability of the Gini index to monitor time and geographic trends in incidence and death during the SARS-CoV-2 pandemic

Manz, K.; Mansmann, U.

Health inequalities across nations reinforce social and economic differences. The European Commission has outlined its commitment to reducing health inequalities. The SARS-CoV-2 pandemic is a disruptive event with global, national, and local effects on every aspect of a society's life. Therefore, it is of interest to quantify and display health (in)equality induced by COVID-19 over time and on different geographic scales (global, continental, national, regional). We aimed to perform a study of (in)equality regarding COVID-19 related incidences and deaths using the Gini index (GI) that was developed to explore inequality in wealth within or between nations. The GI is a relative measure which quantifies the ratio of the mean absolute difference between observations and their mean: GI=0 describes a situation where everybody owns the same, GI=1 corresponds to one person owning the entire wealth of a society. A specific focus of our analysis is the (in)equality of case-fatality rates. We use global, nation- and statewide data to evaluate the heterogeneity at different levels. We also reflect on the suitability of the Gini index to monitor equality aspects of the pandemic. Data from the SARS-CoV-2 pandemic show a considerable amount of heterogeneity in the global distribution of incidences and deaths. Only few countries contribute largely to the total incidence and death toll. Inequality may result from heterogeneous reporting systems, heterogeneous policy making to fight the pandemic, heterogeneous health systems, and demographic structures. Inequality decreases when going from continental to national or regional levels. Time trends on national level reflect local outbreaks. There is heterogeneity in case fatality rates, too. There is also a specific numeric artefact of the GI: Even if many smaller regions have no COVID-19 related deaths at all, and one region has low (but still non-negligible) number of deaths the corresponding GI is near to 1. We used the Gini index to reflect inequality between incidence and death rates of nations or geographic regions. The interpretation of the differences between reported GIs is not straightforward. However, combined with the information presented by maps, the GI is a useful tool.