Can we estimate crisis death tolls by subtracting population estimates? A critical review and appraisal

In the absence of high-quality data, death tolls are often estimated using ad hoc methods. In this article, we review the use and validity of a set of ad hoc procedures that we term the growth rate discontinuity method, or GRDM. This method estimates the size of death tolls by projecting between pre- and post-crisis population estimates with crude growth rates and then subtracting the projected values. Despite its simplicity, this method is the source of prominent death toll estimates for the Black Death, the 1918 influenza pandemic, the Great Chinese Famine, and the Rwandan genocide, for example. Using statistical simulation and comparisons to the results of better-validated demographic methods, we assess the accuracy, precision, and biases of this method for estimating mortality in absolute and relative terms. We conclude that GRDM requires precision in its inputs to an extent rarely possible in contexts of interest. If one has sufficient data to specify the method well, one can also use a more reliable method; if one lacks that data, GRDM does not provide a valid means of demographic or econometric analysis. The literature that has drawn conclusions about the past and present from this deceptively simple method should be revisited.