Examining the role of international migration in global population projections

Guy J. Abel, Wittgenstein Centre (IIASA, VID/ÖAW, WU)
Samir K.C., Wittgenstein Centre (IIASA, VID/ÖAW, WU)
Nikola D. Sander, Wittgenstein Centre (IIASA, VID/ÖAW, WU)

Advances in projecting international migration have been hindered by a lack of adequate data. Consequently, international projection-making agencies commonly use simplistic assumptions of net-migration measures derived as residuals from demographic accounting. However, past net migration can be often volatile and are known to introduce inaccuracies when projecting populations (Rogers, 1990). This paper presents sets of global population projections to 2060, focusing on two alternative assumptions of international migration. Assumptions on rates of other demographic factors, namely fertility and mortality, are held constant allowing an examination of the role of international migration in global population projections models. In the first projection, we set up the future migration in each country to mirror that of the United Nations Population Division (UNPD). In the second projection, we use a first-of-a-kind set of estimated 5-year bilateral migration flows by sex developed from the flows from stock methodology of Abel (2013). The net migration of the estimates within these flow tables matches those of the UNPD. Estimated bilateral flow tables are further disaggregated using a parametric assumption for emigration age schedules, and then summed over rows and columns to obtain immigration and emigration rates by age and sex. These estimates are used as base data in a bi-regional projection model, where immigration and emigration rates are assumed to remain constant up to 2060. Our results highlight differences in the future level of populations around the globe and numbers of migrant flows between the net migration projection model and the bi-regional projection model.