International migrant stocks

Definition

An international migrant is defined as “any person who changes his or her country of usual residence” (UN DESA, 1998). Stocks are defined as “the total number of international migrants present in a given country at a particular point in time” (UN SD, 2017: 9).

Data sources & measurement

Various sources collect and disseminate migrant stock data at the national and international levels. National statistical offices collect data on migrant stocks through censuses, population registries or administrative sources. The UN Statistics Division (UNSD) is mandated to collect official migration statistics, including on migrant stocks, from countries through the Demographic Yearbook data collection system. The Statistical Office of the European Union (Eurostat) has a similar task for EU Member States. Some governments also report stock data to other international organizations such as the Organization for Economic Cooperation and Development (OECD). UN DESA provides global estimates of international migrant stocks based on national statistics on country of birth, and where data on the foreign-born were not collected in national censuses, based on country of citizenship (UN DESA, 2016: 4; UN SD, 2017). The global data are also disaggregated by sex and age.

To improve the statistics, the UN produced recommendations in 1998 to define an international migrant as "any person who changes his or her country of usual residence" (UN DESA, 1998), distinguishing between "short-term migrants" – those who change their country of usual residence for at least three months but less than a year – and "long-term migrants" – those who do so for at least one year. However, not all countries have adopted such a definition. Some countries may use different criteria to identify international migrants for statistical purposes, such as a different minimum duration of stay in the country. 

Data strengths & limitations

Estimates of migrant stock are available for 232 UN countries/areas and comprise the most geographically comprehensive information on international migration. There are significant regional variations in data availability – almost 20 per cent of African countries and 10 per cent of countries in Asia do not have recent data on international migrant stocks (UN DESA, 2017).

The comparison of national statistics on international migration is difficult at a global level. Countries use different concepts and definitions – some simply using country of birth or nationality to define a migrant. The timing of census data also varies from country to country. Many countries conduct new censuses only every 10 years or so, which means the data can be outdated. UN DESA use interpolation and extrapolation methodologies to estimate stocks for countries where no recent censuses have been conducted. For those countries with only one data point available since 1990 UN DESA use the increase in migrant stocks in the region, or area or country with a similar profile to impute/estimate stocks in a certain year (UN DESA, 2017). There are also several reasons why the number of migrants may be under reported in population censuses. For example, new residents with uncertain legal status are less likely to be included in the censuses (see UN SD, 2017; GMG, 2017).