International migration flows

Definition

Migration flows “refer to the number of migrants entering or leaving a given country during a given period of time, usually one calendar year” (UN SD, 2017). However, countries use different concepts, definitions and data collection methodologies to compile statistics on migration flows. Definitions of who counts as an international migrant vary over time in the same country and across countries.

Data sources and measurement

Statistics on migration flows are based on a variety of data sources depending on the country. Countries may calculate migration flows based on information from administrative sources, such as data derived from issuance of temporary or permanent residence permits and population registries, or they may use sample survey data. Some countries report data on annual flows to the UN Statistics Division (UN SD), who has a mandate to collect migration statistics, including on migration flows, from countries through the Demographic Yearbook data collection system. Some countries report data to OECD or the Statistical Office of the European Union (Eurostat) as well. OECD data on permanent migration inflows allow to distinguish between different types of migration flows including work, family and humanitarian migration (OECD, 2019). However, the number of countries reporting flow data is limited and the data are often not harmonized.

The UN Department of Economic and Social Affairs (UN DESA) has compiled data on the flows of international migrants to and from selected countries since 2005. The latest Revision, in 2015, contained data from 45 countries that collected this information (only 43 on emigration flows) – a steady increase compared to 15 countries in 2005, and 29 countries in 2008. Eurostat provides flows data disaggregated by age and sex, covering the EU-28, Iceland, Liechtenstein, Norway and Switzerland. In addition, UN SD provides statistics on international travel and migration through their Demographic Yearbook. These migration flows are disaggregated by reason for admission, purpose of staying or going abroad, age and sex. Raymer et al. (2013) also provide bilateral migration flows estimates by sex and age for European countries. Nawrotzki and Jiang (2015) estimated age and sex-specific bilateral net migration flows (the difference between migration inflows and outflows) around the year 2000; the information is contained in the publicly available Community Demographic Model International Migration (CDM-IM) dataset.

Given the lack of flow data at the global level, researchers have developed their own estimates of (bilateral) global migration flows based on 5-year intervals (see Abel and Sander, 2014; Raymer et al., 2013). These estimates are based on UN statistics on changes in migrant stocks over time. Statistics on bilateral migration flows are also available from the DEMIG Country-to-Country database (C2C) of the University of Oxford, which contains bilateral migration flows data for 34 countries, and from up to 236 countries for the period 1946-2011. The database also provides gender breakdowns where available and more historical depth.

The International Organization for Migration’s Displacement Tracking Matrix (DTM), a system to track and monitoring population displacement and mobility, collects migration flows data through flow monitoring component in more than 30 countries. DTM flow monitoring assesses areas of high mobility, often at key entry, exit and transit locations. Flow monitoring activities aim to derive quantitative estimates of the flow of individuals through specific locations and to collect information about the profiles, intentions and needs of the people moving. Tools used under this component include baseline assessments at national and local levels, flow monitoring registries and in-depth surveys. 

Data strengths and limitations

The quantification of migration flows is fundamental for the analysis of contemporary migration patterns, particularly the impacts of different factors and policies in countries of origin and destination. Inflow statistics compiled by OECD are available by category of entry, such as whether people moved for reasons of work (including seasonal workers), family reunification, humanitarian protection or others. Numbers of people moving within areas of free circulation such as the European Union or the Southern Common Market (Mercosur) are also indicated separately in the OECD’s International Migration Database.

However, the availability of international migration flows data are limited:

• Flow data are only compiled for 45 countries worldwide (UN DESA, 2015) or estimated by region.
• Those countries that do report flows often use different concepts, definitions and data collection methodologies which can make the comparison of flows across countries difficult.
• Flow monitoring tracks movement of people in and out of a country, but is limited in recording international migration, distinguishing one-way and circular migration, and using a systematic sampling frame.  
• There are challenges associated with the use of administrative sources to derive statistics on international migration flows: such sources usually record events (e.g. issuance/renewal/withdrawal of a residence permit) and may not necessarily reflect actual migration movements (e.g. a residence permit is not renewed but the person stays in the country, or the permit is renewed but the person leaves the country).