1. How we measure international migration

As we transform the way we produce international migration statistics to better meet user needs, we are developing new methods using a range of data sources.

The data sources we use show international migration (referred to as migration from now on) through two main measures: country of birth and nationality. However, country of birth and nationality can give different perspectives on the statistics.

A person's country of birth does not change. Therefore, it is often the preferred measure when looking at the long-term changes in migration. To look at more recent changes, we recommend combining country of birth with year of arrival (for example, non-UK-born arrived in the last five years).

A person's nationality can change. A person can gain new citizenship (a person's formal membership of a state) and hold multiple passports reflecting different nationalities. Nationality reflects an individual's choice to become a citizen, as well as their ability and eligibility to do so. As nationality can show a person's legal status of a country or countries, it can potentially provide a more recent reflection of migration.

Passports held is another measure that can be used to describe migration statistics. It is often a way of identifying dual or multiple nationality.

Statistics based on migration measures can provide insight into both population size (for example, stocks or levels) and movement of people (for example, flows).

For stocks, we consider the number of people normally resident in the UK at a point in time by country of birth and nationality. For long-term migration flows, estimates are based on the nationality of the number of people recently arriving or leaving the UK for a period of 12 months or more. Both migration stocks and flows are defined using the standard United Nations (UN) definition for usual residence. That is, the country in which a person has a place to live, where they normally spend the daily period of rest for the majority of the year.

See Section 6: Glossary for migration definitions.

Main challenges of measuring migration

Different data sources collect and use the measures country of birth, nationality, and passports held in different ways. This leads to inevitable differences in the statistics produced from each data source. However, all of these statistics are reported under the term "international migration," which can lead to confusion. 

The way these measures are described is also often confused. The term "foreign national" is used frequently, and sometimes this statement is mistakenly used when referring to country of birth instead of nationality data. Nationality is also regularly confused with national identity or ethnicity.

This guide addresses these misunderstandings and helps users to interpret the measures correctly.

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2. Recommendations for use

When describing migration statistics, it is important to ensure these statistics are clear for all users. The following are recommendations of how to use the current definitions and measures.

Intended use of migration measures

1. Users should decide whether country of birth or nationality is the most appropriate measure to report.

Typically, a person's country of birth does not change. Therefore, it is the preferred measure when looking at the longer-term impacts of migration and the population of people who have moved to the UK over the course of their lifetime. Whereas nationality of a country is a legal status and can change if new citizenship is gained, and multiple passports can be held. People who move to the UK only become eligible for citizenship after a number of years. However, some non-British nationals never acquire British citizenship even after long periods of residence.

2. Users should decide if they want to report on nationality or national identity, to avoid misusing the terms.

There can be confusion regarding the two terms unless there is clear clarification on the difference between them. Users need to be clear about the distinction between national identity, which is a self-identified indicator of cultural identity and nationality, which is a legal status of a country or countries.

3. Users should be aware that ethnicity is not a measure of migration.

There is no consensus on what constitutes an ethnic group, and membership is something that is self-defined and subjectively meaningful to the person concerned. Since ethnicity has many different aspects, various possible ways of measuring ethnic groups are available and have been used over time. These can include country of birth, nationality, language spoken at home, skin colour, national or geographical origin, and religion. What is generally accepted, however, is that ethnicity includes all these aspects, and others, in combination.

Consistency of language

4. Users should use the right terminology when reporting migration statistics.

Country of birth, nationality, citizenship, and passports held are sometimes used interchangeably when reporting on migration statistics. When this happens it makes interpretation unclear and can cause confusion. It affects the comparability, coherence and consistency of statistics and reporting. Therefore, there needs to be clear, concise, and comprehensive explanations of what each statistic is measuring. Using the definitions in Section 6: Glossary will help ensure that terms are used correctly and that users are clear on what each term means.

Accurate reporting

5. Users should clarify or check that the terms they are using in the data and statistics match how the user is interpreting and reporting them.

This will minimise the misreporting of statistics.

6. Users need to identify and report the associated caveats related to each data source.

There are caveats on the migration measures associated with every data source. These should be carefully considered when users are reporting on the data and statistics. The main caveats are described in the data descriptions of Section 3: Country of birth, Section 4: Nationality, and Section 5: Passports held.

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3. Country of birth

Definition

Country of birth is the country in which a person was born. This is different to nationality which is the country or countries where a person can have a legal status, although they may not reside in that country.

There are times when someone is not born in a country (for example, at sea). In this situation the country where the birth is registered is usually used.

Country of birth does not change, except as a result of an international boundary change. For example, Czechoslovakia, where people could be born in Czechoslovakia, the Czech Republic or Slovakia, but their nationality will be one of the last two as the first no longer exists. 

Data that contain country of birth

At present there is limited availability of country of birth collected on administrative data. Most of the data sources that collect a person's country of birth are survey based.

Census

The census takes place every ten years in the UK and asks the respondent to provide the country of birth for each member of the household.

International Passenger Survey (IPS)

The IPS gives information about travel in and out of England, Wales, and Scotland. It collects the country of birth as stated by the passenger in the interview.

Labour Force Survey (LFS) and Annual Population Survey (APS)

These are household surveys covering the whole of the UK. They ask the respondent for the country of birth of each member of the household.

When to use it

As a person's country of birth typically does not change, it is sometimes preferable to use when analysing the UK resident population. As it remains constant across time it is a consistent measure of long-term migration and is not affected by rates of successful British citizenship applications. Statistics by country of birth are useful in understanding the longer-term contribution of international migration to the UK, including people who have moved to the UK and since changed their nationality.

Main challenges

Self-reporting

For each of the data sources, the person's country of birth is self-reported, and no evidence is asked to validate their answer. In a small number of cases, there is a potential for bias, where a person may give an answer that they see as more socially acceptable or through fear of discrimination.

Limited insights into migration patterns

Country of birth alone does not give much of an indication of migration patterns. To look at more recent changes, we recommend combining country of birth with year of arrival (for example, non-UK-born arrived in the last five years).

British nationals born abroad

Some individuals may be born abroad but are British nationals, either through entitlement or naturalisation. This means they will appear in migration datasets as non-UK-born despite being a British national.

Example:

Lucy and both their parents are British nationals. Lucy was born while their parents were working in the armed forces based overseas in Cyprus. They are therefore recorded as non-UK-born, so will appear in the migration data and statistics when looking at country of birth.

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4. Nationality

Definition

Nationality of a country is a legal status that usually gives a person a particular set of rights relating to that country. It can be possible for someone to have two or more nationalities, often referred to as dual or multiple nationality.

The measures citizenship and passports held are often collected and used interchangeably with nationality. In general, this will be appropriate for most people, but it is not the case for everyone.

Difference between nationality and passports held

For a lot of people nationality and passports held will be the same. However, for others who hold multiple passports, or have more than one nationality, then these can differ.

In some data sources nationality is determined through what is stated on the person's passport. However, in other cases passports held is a separate question and the person is directly asked what passports they hold. Therefore, in these cases it is possible for a person to state that their nationality is different to what is on their passport.

Difference between nationality and citizenship

Citizenship is a status that identifies a person's formal membership of a state, entitling them to hold a country's passport.

The measures nationality and citizenship are often used interchangeably. The measures can differ across countries. To use British citizenship and nationality as an example: British citizenship is a type of British nationality. This means someone can have a British nationality without being a British citizen.

Difference between nationality and national identity

Nationality is often mistaken for national identity, which is a measure of self-identification. National identity is subjective, as it allows a person to express a preference as to which country or countries they feel most affiliated to, regardless of their actual nationality. For example, a person may sometimes respond Welsh and other times British.

Data that contain nationality

Data sources have different ways of defining and collecting information on a person's nationality.

Census

A proxy for nationality is derived using the passports held question. The census question does not allow for any indication of a "primary" passport or identification of nationality. Therefore, we prioritise in the following order to derive nationality:

  1. British 

  2. Irish 

  3. Other country

Exit Checks

Exit Checks data from the Home Office Initial Status Analysis (ISA) system combine visa and travel information to link a person's travel movements into and out of the country. The primary nationality variable is derived in the following priority order:

  1. most recent passport scan at a border

  2. nationality on visa application

  3. most frequent nationality appearing on Advance Passenger Information (API)

The API is data sent to the Home Office by carriers from aviation, maritime and rail sectors based on what passengers and crew provide in advance of travel.

International Passenger Survey (IPS)

The IPS gives information about travel in and out of England, Wales, and Scotland. It collects the nationality and citizenship of the person from the passport which is being used at the time of the interview.

Labour Force Survey (LFS) and Annual Population Survey (APS)

These are household surveys covering the whole of the UK. They ask the respondent to report the nationality of each member of the household.

Registration and Population Interaction Database (RAPID) and Migrant Worker Scan (MWS)

RAPID is created by the Department for Work and Pensions (DWP) to provide a single coherent view of citizens' interactions across the breadth of systems in the DWP, HM Revenue and Customs (HMRC) and local authorities via Housing Benefit.

Nationality on RAPID is collected through the MWS. The MWS collects nationality through two ways. It may be based on the person's passport used as the identity evidence at an interview for a National Insurance Number (NINo) application. Alternatively, if a NINo is allocated as part of a visa application process, then the nationality is recorded from the document provided as part of the visa application.

Higher Education Statistics Authority (HESA)

HESA record the legal nationality of the student. This is compulsory for all students at providers in England, Wales, and Scotland and optional for students at providers in Northern Ireland. HESA also records the postcode of the student's permanent or home address prior to entry to the course, this is referred to as the student's domicile.

When to use it

Nationality can change over time if new citizenship is gained, meaning it is a changeable measure.

Nationality reflects an individual's choice to become a citizen as well as their ability and eligibility to do so. As nationality can show a person's legal status of a country or countries, it can potentially provide a more recent reflection of migration.

When analysing nationality, it is important to note that this does not fully reflect the immigration status or the rights and entitlements of individuals to work and access services in the UK. 

Main challenges

Self-reporting

Some data sources, like IPS and Exit Checks, require evidence to be given when providing information on migration, such as a passport or travel card. However, other data sources such as the LFS or APS, ask the person what their nationality is. Therefore, it is self-reported, and no evidence is asked for to validate this. This means there is potential for bias in how someone responds.

If there is no definition given, the respondent may interpret their nationality as their self-identified national identity. Also, people with multiple nationalities may not declare all that they have, or the opportunity to provide this information may not be given. This could mean dual or multiple nationality is not identified.

Example:

Imran was born in Pakistan but attended school in the UK and continued to stay for employment. They never chose to apply for a British passport, as they received a permanent settlement visa alongside their family, so they continue to hold only a Pakistani passport. Having lived in the UK most of their life and culturally feeling British, when asked on a survey what their nationality is, Imran responds that they are British. 

Changes in nationality

Data sources collect information on a person's nationality through either the passport they hold or their self-reported nationality. Someone's nationality can change, yet this is not always reflected in the data. Both issues could lead to different results from different data sources.

Some data sources are rarely updated for changes in nationality. For example, in the MWS and RAPID, nationality is only recorded at the point of NINo registration, so is not updated for changes in nationality. Someone could register for a NINo early in their time in the UK when they are a non-British national, but subsequently acquire British citizenship. In the MWS, they would remain recorded under their non-British nationality.

Alternatively, in Exit Checks, generally nationality is recorded as the passport held at time of travelling or applying for a visa, so this might not be the passport best aligned to their nationality. The person may hold other nationalities which may not be recorded.

Example:

Jackson moved from Canada to the UK for a new job eight years ago. Before starting work in the UK, they applied for a NINo using their Canadian passport. Last year Jackson became a British citizen by naturalisation (the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country). On all surveys they now declare their nationality as British. However, as the MWS is not updated for changes in nationality, their nationality would still show as Canadian, for example in an analysis of employment using RAPID.

Dual or multiple nationality

Many data sources only collect one nationality so there is potential for undercounting people who are dual nationals and hold multiple passports. Increased global movement may have increased the number of dual nationals.

Exit Checks, IPS and MWS all define nationality as what is stated on the person's passport. However, if someone has dual nationality and holds more than one passport, they are more likely to travel on the passport most likely to ensure smooth entry to the country they are entering, rather than the one which they consider to be most aligned to their nationality.

There is also a chance that people may not declare dual nationality or other passports they hold. In particular, dual nationals travelling in the UK are more likely to use their British passport. Some data sources allow for collection of multiple passports, such as the LFS, APS and the census. However, overall, the inconsistency across sources can lead to different reporting for migration because of dual nationality. 

Example:

Lamai was born in Thailand but moved to the UK ten years ago to firstly study then work. They have since claimed British citizenship and a British passport. However, they retain their Thai passport as their family live there and they have cultural ties to the country. In most data their nationality is British. However, on some surveys they can declare that they also hold a Thai passport, including on census and LFS or APS under the passports held question. Also, occasionally when traveling back to Thailand, they travel on their Thai passport, and this could lead them to being recorded as having Thai nationality on some data sources.

Limited insights into migration patterns

Nationality alone does not give a full indication of migration patterns. Additional information such as where and when a person has recently migrated from (for example, previous country of residence or previous nationality) is useful in providing more insight.

Acquiring overseas citizenship and nationality

In some countries people can acquire nationality or passports without ever living there. For example, in some countries, such as the United States or Denmark, a child is likely to be eligible to acquire citizenship and therefore nationality at birth for that country if a parent is a national. Therefore, the child can also apply for a passport. Another scenario is in Malta where a person can buy a Maltese passport and therefore be considered a Maltese national, yet they did not need to have had resided there.

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5. Passports held

Definition

Passports held is the country or countries that a person has a passport for. This can include expired passports if a person is entitled to renew it.

Passports held is therefore a separate question to asking someone's nationality.

Data that contain passports held as a separate question

Census

The census allows a person to record multiple passports that they hold. It does not allow indication of a "primary" passport.

Labour Force Survey (LFS) and Annual Population Survey (APS)

These are household surveys covering the whole of the UK. These allow the respondent to state up to two passports they hold or are entitled to hold.

Main challenges

Multiple nationalities

Passports held data are often a way of identifying dual or multiple nationality.

The LFS allows a respondent to state whether they hold a UK, Ireland, other or no passport. There is space to report up to two other passports.

The passport(s) held question on the census was first asked in 2011 and allows people to enter the country for each passport they hold, enabling multiple passports to be recorded. This gives an indication of dual or multiple nationality.

Example:

Noah was born in Australia and claimed an Australian passport. Aged 18 years, Noah moved to New Zealand to study but then stayed on to work. They then went onto claim a New Zealand passport, while still retaining their Australian passport. Five years ago, they were redeployed with their job to the UK. Here they met their partner who they later married. Noah has now claimed a British passport, while still retaining their other passports. When nationality and passport data are collected, Noah will often only be able to declare one of their passports. However, in the LFS and census they can declare all three. 

Acquiring overseas passports

In some countries people can acquire passports without ever living there. For example, in some countries, such as the United States or Denmark, a child is likely to be eligible to acquire citizenship at birth for that country if a parent is a citizen and so the child can apply for a passport. Another scenario is in Malta where a person can buy a Maltese passport and therefore be considered a Maltese citizen, yet they did not need to have had resided there.

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6. Glossary

Country of birth

The country in which a person was born.

Nationality

Nationality of a country is a legal status that usually gives a person a particular set of rights relating to that country.

Dual or multiple nationality

Someone who holds two or more nationalities. Some countries do not allow dual nationality, for example China and Nepal. To gain British nationality in this situation, a person would need to renounce their current citizenship of the other country.

Citizenship

A status that identifies a person's formal membership of a state, entitling them to hold a country's passport.

Naturalisation

The process of becoming a citizen of another country.

Passports held

The country or countries that a person holds, or is entitled to hold, a passport for. This can include expired passports if a person is entitled to renew it.

National identity

National identity is a measure of self-identity. This is because each person will have a different idea about the meaning of "national identity". A question on national identity allows a person to express a preference about which country or nation they feel most connected to.

Ethnicity

Ethnicity is a multifaceted and changing phenomenon, and various ways of measuring ethnic groups are available and have been used over time. These include country of birth, nationality, language spoken at home, skin colour, national or geographical origin, and religion.

UK-born

A person born in the UK (England, Scotland, Wales, and Northern Ireland).

Non-UK-born

A person born outside of the UK. 

British national

A person who holds a type of British (English, Scottish, Welsh, and Northern Irish) nationality. There are six different types of British nationality

  • British citizenship 

  • British Overseas Territories citizen 

  • British overseas citizen 

  • British subject

  • British national (overseas) 

  • British protected person 

Non-British national

A person who does not hold British nationality.

British citizen

A person with British nationality usually through a connection with the UK: birth, adoption, descent, registration, or naturalisation. They can live and work in the UK free of any immigration controls.

Non-British citizen

A person who does not hold British citizenship.

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8. Cite this methodology

Office for National Statistics (ONS), released 25 August 2022, ONS website, methodology, Guidance on using country of birth, nationality and passports held data

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Manylion cyswllt ar gyfer y Methodoleg

Megan Bowers
pop.info@ons.gov.uk
Ffôn: +44 1329 444661