Uncertain Population Futures: Critical Reflections on the IHME Scenarios of Future Fertility, Mortality, Migration and Population Trends from 2017 to 2100
Stuart Gietel-Basten1, Tomas Sobotka2
1Hong Kong University of Science and Technology, 2Vienna Institute of Demography / Wittgenstein Centre
In July 2020 The Lancet published global scenarios of fertility, mortality, migration and population trends from 2017 to 2100 produced by the research team from the Institute for Health Metrics and Evaluation (IHME) (Vollset et al. 2020). These projections, based on a vast amount of data, complex estimates and models, have gained high visibility, also in subsequent media coverage and interviews. Yet, IHME highly publicised population data and scenarios suffer from numerous issues with the underlying data, models and scenarios as well as over-simplistic interpretations of their results. This study aims to substantiate our concerns, spelled out earlier in a letter to the Lancet (Basten, Sobotka et al. 2020), and review major issues and weaknesses with IHME projections and their interpretation.  In conclusion, we highlight internal inconsistencies in the IHME modelling approach, which lead to questionable projections for many countries and scenarios.