François Pelletier United Nations Population Division, New York

1. KNOMAD, Migration SeminarNew York, April 29 2014 World Population Prospects: an overview of the migration component François Pelletier United Nations Population Division, New York www.unpopulation.org

2. WPP: Population estimates and projections • Cohort component method (5*5) • Population, births, deaths and migrants (1950-2100) • Indicator: Net international migration (absolute numbers; policy; world balance, abc…xyz)

3. Data • Census information, stocks, data on migration workers, etc. • UNHCR refugee statistics

4. Procedures and assumptions • Estimation part: 1) Use the information that is made available. 2) Growth Balance methods: Consistency between population counts and the components of population change is achieved in several countries or periods by assigning to net international migration the residual population estimate obtained by comparing the actual intercensal population growth rate with independent estimates of natural increase based on fertility and mortality estimates. Within this exercise, adjustments in population counts are sometimes considered or assumed. • Projection part: • Constant levels till 2050 and then decline linearly to zero by 2100 (this last part was adopted when the projections were extended till 2100 in the 2010 Revision). • Some adjustments in the levels are often needed in the initial periods; converge rapidly to “zero” net migration in some countries 3) Return migration (e.g. refugees, labour migrants in GCC countries).

5. Migration patterns • The distribution of migrants by sex is established on the basis of what is known about the participation of men and women in different types of flows for any given country (i.e., labour migration, family reunification, etc.). Models are often used to distribute the male and female migrants by age group according to the dominant type of migration flow assumed (see Castro models). • When the age and sex distribution of international migrants is known, those distributions are used to determine which model is most suitable or, in some cases, those data were used directly as input. The distribution of net migrants by age and sex is often kept constant over the projection period. However, if a country is known to attract temporary labour migrants, an effort is made to model the return flow of those labour migrants. The same idea is applied to refugee flows.

6. Impact of migration assumptions on accuracy of population projections • High-fertility countries vs Low-fertility countries • Small countries (population wise, including small island States) are where “errors” in projected levels of international migration are likely to have the greatest impact on the accuracy of our population projections

7. Contribution of demographic components to population growth by 2050 as proportion of the total population in 2010

8. Moving forward • Revise past estimates • Re-evaluate some of our assumptions, including after 2050 • Establish more consistent procedures, including the development of return migration schedules • Consider using demographic criteria (growth rates, relative changes in working-age populations) to guide some of our assumptions. High-fertility countries (e.g. Nigeria, etc.) vs. countries with declining working-age population (e.g. China, etc.) • Matrix with top “x number” of countries of origin/destination! • Future levels and trends of international migration will also be driven by economic, political and policy changes that are not easy to predict over several decades • Considering that we are doing projections for 200 countries till 2100, there might be some value in keeping it simple!