Where do assumptions come from?: Investigating the substantive basis for population projections in Europe

Wolfgang Lutz, International Institute for Applied Systems Analysis (IIASA)
Samir K.C., International Institute for Applied Systems Analysis (IIASA)
Isolde Prommer, International Institute for Applied Systems Analysis (IIASA)
Christopher Wilson, International Institute for Applied Systems Analysis (IIASA)

Assumptions drive projections. The arithmetic of making cohort-component population projections has essentially been unchanged since Edwin Cannan proposed it in 1895. However, the way in which demographic forecasters make their assumptions concerning future trends in fertility, mortality and migration is always potentially changing. This paper addresses two main issues. The first part documents current practice in assumption-making in Europe, drawing on national and European publications, and on the results of a questionnaire sent by Eurostat to all national population forecasters in the EU-25. The second part considers new proposals for systematically collecting and integrating expert argument about future trends. These could lead to best-practice methods for making assumptions in the future.