As highlighted by recent political developments in several UNECE countries, migration continues to play a substantial role in shaping responses to economic and foreign policy challenges. Member countries of the United Nations recently emphasised the importance of addressing migrant movements in a comprehensive way in the New York Declaration for Refugees and Migrants. However, simply counting those who do not remain in one location is a challenge for statisticians.

One common way of collecting data is directly from migrants by asking migration-related questions through decennial censuses or targeted surveys. Censuses cover the entire population, but are infrequent, costly and collect only limited information due to concerns over burdening respondents with too many questions. Targeted surveys can be more frequent and more detailed, but add uncertainty because data are based on only a sample of the population. Both surveys and censuses also depend on the accurate recollection of respondents.

Administrative data can move past such recall problems. Population registers provide many gains to residents by simplifying administrative tasks and, if accurately maintained, creating a basis for many types of statistics including those for migration. The upfront costs of setting up such registers are high and require a high level political decision. Border control data can be more or less relevant for countries depending on geography and freedom of movement agreements. However, even in countries for which borders are strictly controlled, it remains difficult to distinguish in border crossing data those who come for a short-term from those who change their place of residence. Other administrative data such as work permit applications or education registration may be useful as an additional data source.

More detail on these methods can be found in the UNECE’s recently published Handbook on the Use of Administrative Sources and Sample Surveys to Measure International Migration.

With all methods of data collection, two areas remain significant challenges. The first is measuring undocumented migration. By definition, these migrants will not be counted through most administrative sources. In addition, such persons may be reluctant to respond to censuses or surveys for fear of legal consequences.

Second, accounting for persons no longer present in the country also poses a problem. Surveys can ask questions on former neighbours or family members who have left the country, but these data may not always be accurate and do not capture cases where entire families move. In theory, population registers or other administrative records could address this population, but given the benefits that can be maintained if one remains registered in a country, emigrants often fail to deregister. The UNECE’s Guidelines for Exchanging Data to Improve Emigration Statistics identifies data sharing as one way to help improve these data – that is, using immigration data from receiving countries. The UNECE’s Migration Clearing House contains data that can be used for such purpose, among others.

Beyond counting the number of migrants, there is a policy interest in their socio-economic characteristics. To better address this topic, the UNECE has worked to identify harmonized indicators that can be used to compare data between countries. The publication Measuring Change in the Socio-Economic Conditions of Migrants contains guidance for statisticians as well as a review and recommendation of possible indicators for the demographic, education, economic, and social and civic participation dimensions.

Interest is also growing in new and more specialized topics such as circular migration – repeated immigration and emigration of certain persons. This is a specific category of migration that could under certain circumstances provide a triple benefit of (1) helping countries in need of temporary labour, (2) enabling migrants to develop and gain new work experience, and (3) using new knowledge and skills in their countries of origin after returning. However, the influence of such migrants remains unknown until studies can be conducted on the basis of consistent, comparable data. In the publication Defining and Measuring Circular Migration, UNECE has set the stage for collection of data on this topic.

Much remains to be done for improving the measurement of international migration. UNECE continues to support national statistics offices in these efforts by developing methodologies, building national capacity and disseminating data.