When assessing migration trends from register data, the definition of how a migrant is categorised becomes crucial in the understanding of which types of flows and migrants are actually measured. An overall distinction is made between international migrants and domestic migrants. Crudely speaking, this distinction is related to the type of border the migrants move across rather than a characteristic of the migrants themselves. In other words, if the movement happens across a national border, this is termed international migration, while migration across regional or municipal borders within the same country are domestic migrants.
This the term international migration is not necessarily as closely linked to nationality as the name may seem to imply. This depends on whether the international migrants are determined by last point of residence, by birthplace or perhaps by nationality (-ies). In practice, this means that the flow of people from for example the UK to Sweden, if measured by last point of residence, contains also the return migration of Swedish nationals. If the same UK to Sweden flow is measured by either place of birth or nationality, it will be possible to distinguish the share that Swedish nationals constitute of these UK-SE flows, as well as any other nationals. Whether to favour place of birth or nationality for this, relates both to a frequent question of data availability but also what is the most relevant characteristic to measure as people may change their citizenship during their lifetime while place of birth is a fixed variable.
If all types of variables are available for the migration flow, one would like to measure, the selection of data comes down to a question of what we want to measure: is it the sum of flows of people between two countries; the flow of certain nationalities between these two countries; or is it the composition of this flow with regard to nationality and/or birth place that is interesting? Another aspect of the birthplace versus nationality issue is that also countries change. One popular example is the breaking up of the Soviet Union whereby migrants that had left during the Soviet times, would have been registered with ‘Soviet Union’ as their place of birth, while they may actually have been born in, for example, present-day Estonia. Some national statistical offices have chosen to correct these Soviet migrants’ place of birth in retrospect but not all, so this is an important issue to be aware of. Yet another aspect is the situations where there is no distinction in nationality between two countries/regions. One Nordic example is the flows between Greenland and Denmark, where all have Danish nationality but place of birth registration makes it possible to distinguish between people born in Denmark and people born in Greenland. However, due to the special administrative division between Denmark and Greenland, the Nordic statistical offices registers are not in unison about how to publish data on the Greenlandic population.
Fow example, Statistics Norway separates Denmark, Greenland and the Faroe Islands, while Statistics Sweden does not. One desire that often arises for those concerned with measuring migration flows is even more detailed socio-economic information on the migrants as well as the motivations behind the migration decisions. Some attempts are made in the Nordic countries where immigrants by surveys are asked to characterise themselves (e.g. by education level) and/or their motivations for migration (e.g. asulym, work, study, family) but this is not systematic nor practised across time, countries and regions. Another weakness of this type of registration is that such characterisations are not fixed: education level may change shortly after the migrants’ arrival, just as it can be difficult to validate their selected motivation category. For example, while the initial motivation for immigration – and more importantly the permit for entry – may be study and/or work, the underlying motivation for applying to a specific country could rather be a desire to move to the country of a significant other. Thus, the primary reason for the individual may more appropriately be termed ‘family reasons’ and the study/work just the tool that made such a unification possible, and in general the motivations behind migration are often more blurred than a simple reply to such a survey question would imply.
Domestic migration is mainly assessed as flows across regional and/or municipal borders, in other words permanent moves between local administrations within the country. As the aim is often to assess the stock of population and the population development in these administrative regions, accounts of net-migration are often sufficient. However, this does not reveal anything about the composition of the people moving between regions/municipalities, and therefore inquiries into age or gender compositions can in most Nordic countries be assessed on rather detailed level while inquiries into these domestic migrant’s nationality and/or place of birth are not nearly as readily available.