International migrant stock is the total number of international migrants in a country at a particular point in time (usually mid-year or end-year) while international migrant flow is the number of international migrants entering or leaving a country over the course of a specific period, usually one calendar year. Migration flows are crucial for understanding migration patterns and trends or how different factors and policies are affecting international migration (IOM, 2020). However, in 2015 only 45 countries were reporting flow data to the United Nations, while data on migrant stock are available for 232 country/areas (UNSD, 2015). Stock and flow data reported by countries are being published by:
- UNDESA
- OECD
- Eurostat
- The World Bank
- The International Migration Institute
- IOM’s Displacement Tracking Matrix
Statistics of migrant stocks and flows must take into consideration not only the departures and arrivals of foreigners/foreign-born but also potential births and deaths as well acquisition of citizenship at birth/through naturalization and loss of citizenship through revocation/renunciation. The 2021 revision to the 1998 recommendations highlights the current misalignment between international migration flows which often capture all persons immigrating (emigrating) to (from) a country in a given year and international migrant stock which refer to all residents with a different country of citizenship or country of birth. The production of population projections and estimates is undermined when stock and flows are based on a different measurement of international migration (UNSD, 2021)
Measuring international migration flows can be complex and challenging, particularly in the context of population censuses which are only conducted every five or ten years. Using the place of previous residence question to determine migration patterns may not capture multiple moves within a one- or five-year period. Furthermore, counting migrants in a census can become even more challenging if they emigrated with their entire household. Given the limitations posed by censuses in providing accurate data on migration flows, it is crucial to acknowledge the importance of alternative data sources. Due to the substantial lag between censuses, they are typically more effective in yielding comprehensive data on migrant stocks, whereas administrative records are more suitable for continuously tracking migration flows (more on the strengths and limitations of different data sources for measuring stocks and flows in Part II, Chapter 2).
What are the key international mobility indicators for reporting?
The UN Expert Group on Migration Statistics distinguishes between different “indicators”, or measurable quantities that can be used to quantify, compare, monitor, or asses particular policy areas and their prioritization. For example, core indicators are those that all countries should strive to collect while additional indicators are those that countries may consider collecting based on national priorities. These indicators are key to improving the measurement of international migration and temporary mobility stocks and flows. Furthermore, the Expert Group suggests several primary topics or disaggregating variables upon which the tabulations of indicators are based. See Table 1 for the core migration indicators for measuring international mobility and how they should be disaggregated (UNSD, 2022b).