Different data sources define migrants in different ways, and in some cases this will affect how the data should be interpreted. The sources in this guide include data that break the population down by: (1) country of birth; (2) nationality; (3) passports held; (4) domicile; (5) legal status, e.g. asylum seeker or refugee; (6) length of stay; and (7) main language spoken at home. Some data sources also distinguish between long-term and short-term migrants, where long-term migrants are those moving for at least 12 months. The Migration Observatory briefing, Who Counts as a Migrant?, provides a more detailed discussion of the implications of using different definitions.
Where a data source allows analysis by both country of birth and nationality, this briefing uses country of birth as the default option, because country of birth cannot change over time but nationality can. Migration data by country of birth cover those who were born abroad and then migrated to the UK, including UK citizens who acquired UK citizenship through either their parents or naturalisation. Migration data by nationality exclude migrants who have become UK citizens. Caution is therefore required when using these data to examine trends in the population of non-UK citizens living in the UK. Nationality may be a more useful metric in certain circumstances, however, such as when examining EU citizens in the context of Brexit or if there is a particular interest in people who have been unable or have chosen not to become citizens.
Some data sources measure movements into (immigration) or out of (emigration) the country. These are often referred to as ‘flows’. Net migration is equal to the difference between the inward and outward flows (immigration minus emigration).
Other data sources measure populations at a given point of time. These are often referred to as ‘stocks’.
The country groupings used in this guide do not include the UK and are as follows:
EU-14: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Italy, Luxembourg, Netherlands, Portugal, Republic of Ireland, Spain and Sweden
EU-8: Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia
EU-2: Bulgaria and Romania
EU-27: All EU countries listed above plus Cyprus, Croatia and Malta.