Obtaining data on specific migrant groups

Which data sources for international migration?

International migrant stock can be estimated from surveys and censuses by asking about the country of birth/country of citizenship and place of residence. Or even better, international migrant stock data can be accessed from the country’s registry of foreigners. Administrative records and border admissions data are a major source of information on the flows of international migrants. However, entries by the same individual would need to be linked by a unique PIN to avoid double-counting migrants. Furthermore, although work and residence permits are a much better source of international migrant flow data than household surveys or population censuses, such permits also cover migrants’ dependents. Temporary mobility or ‘movers’ might be identified a) by including questions on time of arrival in country in surveys and censuses; b) by including a question on intended duration of stay on entry cards; and c) from short-term work permits.

Which data sources for emigration?

Collecting data on emigrants is more challenging as most countries rely on emigrants to report their emigration to the respective consular offices abroad, or on the destination country’s authorities to collect that data. Practical ways of identifying emigrant stock, or citizens residing abroad include:

  • Using destination countries’ migrant stock data, but the key issue with data from other countries is that not all countries define place of residence in line with international standards (e.g., residence at least 12 months or six months and one day)
  • Including questions in household surveys about household members that are currently residing abroad, household members that migrated in the last 12-24 months but have returned and household members who intend to go abroad.
  • Including questions in the census about the place of residence of all children of mothers in the household. Censuses tend to capture only limited information on emigration. They can collect data on emigrated individuals by asking questions to the members of the household still in the country. This approach is used in the Republic of Moldova and Jamaica, two important emigration countries. 
  • Collecting the data from international departure cards, which can be useful for differentiating between international emigrants and residents temporarily abroad (by including a question on intended duration of stay) and for identifying for-work emigrant workers.
Which data sources for internal migration?

Questions from population censuses and household surveys on place of residence at birth or one or five years prior to enumeration can also be used to produce statistics of internal migration. Internal migrants can then be classified as rural-rural, rural-urban, urban-urban or urban-rural based on information about the current and previous type of residence (e.g., farm, village, town, suburbs of city, or city). The most attractive feature of census data is their coverage, which is intended to comprise the entire population. However, it is also possible to produce statistics of internal migration using data from household surveys with relatively modest sample sizes, ranging from 5,000 to 30,000 households. The disadvantages of using these data sources for studying internal migration is that the data are sometimes only available at the aggregate level (e.g., regions), the boundaries of geographic units or the classification of areas as rural or urban may change over time and the thresholds for defining urban areas vary considerably across countries. One way of circumventing these challenges is categorizing places of residence based on external population density data (Kirchberger, 2021).

Call detail records (CDR), which are typically used by mobile phone companies for billing purposes, are a powerful source of data on internal and temporary migration. Blumenstock and Eagle (2019) used CDR to study internal migration in Rwanda, by defining a person’s location as the district of the cell phone tower where the person’s device spends the majority of hours between 6pm and 8am and classifying those who spend x consecutive months in one district before spending the same amount of time in another district as migrants. The advantages of this data source are that a) it allows flexibility in the definition of a migration event (i.e., the period of residence in each location can be modified unlike in a census or survey); b) it measures actual movement as opposed to asking respondents retrospectively; c) it provides spatially disaggregated origin/destination locations, especially if locations are provided at the level of GPS coordinates instead of towers; and d) it provides continuous information about a large subset of the population at a relatively low cost. However, not everyone has access to a mobile phone, a mobile phone may be shared by multiple individuals, some countries may have multiple mobile operators and some users may have multiple SIM cards, network coverage may different across spaces and CDRs usually don’t provide information on the user’s socio-demographic characteristics (Kirchberger, 2021).

Which data sources for circular migration?

Data on circular migrants can be generated based on registrations and de-registrations from the population register or register of foreigners, provided that each person has a unique PIN for linking the data. This is done by selecting individuals with at least 3 (de)registrations. However, this is method may be prone to inaccuracies as immigrants may not have to register until after a defined period, de-registration may happen ex-officio which means the duration is not exact and there are usually no incentives for emigrants to de-register (UNECE, 2016a). Border data on the dates of when people arrive and exit can also be used to identify circular migrants or emigrants, also provided that each person has a unique PIN, but incomplete coverage, double counting, and little to no information about the reasons for travel are major concerns with border data. Embassies and consulates may be able to provide data on citizens granted (seasonal) work permits or residence permits, enabling the identification of circular emigrants. Circular migrants can be identified through household surveys by asking about the most recent entry in country and whether this was their first time entering, however circular and temporary migrants are likely to be under-sampled in household surveys (UNECE, 2016b).