1. What is international migration?

International migration is the movement of people from one country to another and is often defined by the period of time they live in each country.

International migration flows are measured by estimating immigration, emigration and net migration.

Immigration is the number of people coming to live in the UK (inflow) and emigration is the number of people leaving the UK to live elsewhere (outflow).

Net migration is the difference between immigration and emigration (the balance). When immigration is higher than emigration net migration is above zero. This means that more people are coming to live in the UK than are leaving so migration is adding to the UK population.

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2. Who is an international migrant?

There are a number of ways to define an international migrant. We publish statistics on both long-term and short-term international migration.

A long-term international migrant is “a person who moves from their country of usual residence for a period of at least 12 months” (UN definition).

A short-term international migrant is “a person who moves to a country other than that of his or her usual residence for a period of at least 3 months but less than a year except in cases where the movement to that country is for purposes of recreation, holiday, visits to friends and relatives, business, medical treatment or religious pilgrimage” (UN definition).

The UN definition of a short-term international migrant therefore focuses on those migrating for work or study. We also publish short-term international migration statistics for those migrating for 3 to 12 months for all reasons for migration and for 1 to 12 months for all reasons for migration.

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3. How has long-term international migration changed over time?

Levels of both long-term immigration and emigration are higher now than they were 50 years ago. In the 1960s and 1970s, more people left the UK than arrived here each year. In the 1980s, immigration began to exceed emigration each year and since 1994 net migration has been positive with migration adding to the total UK population. Since the late 1990s, the number of migrants has increased further, notably in 2004 when the EU expanded to include 10 new countries.

The international migration timeline shows immigration, emigration and net migration as well as some important events, from 1964 to the latest final estimates.

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4. What is the difference between a migration flow and a migrant stock?

Flows – the number of people moving into and out of the UK provide information on the flow of the population. The International Passenger Survey (IPS) and the Long-Term International Migration (LTIM) estimates are used to measure migration flows.

Stocks – the number of non-UK born or non-British citizens resident in the UK at a given point in time, provide a stock measure of the non-UK population. Population by country of birth and nationality estimates are an example of stocks and are measured by the Annual Population Survey (APS).

Data on flows and stocks cannot be directly compared and may appear to display different trends. For example, despite a decrease in immigration or net migration, the non-UK population resident or working in the UK could still be increasing. This is because as long as net migration is positive and migrants’ deaths do not exceed net migration, there are still more people arriving in the UK than leaving so migration will still add to the non-UK population. To understand the comparability of flows and stocks data see “Why do flows and stocks data not match?

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5. How is long-term international migration measured?

There is no single source that can provide a measure of all movements of people into and out of the UK. We use a combination of data from different sources to calculate our official Long-Term International Migration (LTIM) estimates, which are published every quarter in the Migration Statistics Quarterly Report.

Estimates of LTIM are about 90% based on data from the International Passenger Survey (IPS), a sample survey carried out at all main ports. The IPS captures migration intentions and is used to identify international migrants entering and leaving the UK.

To estimate LTIM, the IPS data are supplemented by Home Office and Northern Ireland Statistics and Research Agency (NISRA) data and several adjustments are made to provide a more complete estimate of migration (Figure 1).

Further information is provided in Long-Term International Migration estimates methodology.

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6. How is short-term international migration measured?

National estimates of short-term international migration are produced directly from data from the International Passenger Survey (IPS) and published annually in the Short-Term International Migration (STIM) for England and Wales bulletin. Estimates of STIM are produced for England and Wales and for local authorities.

Estimates of short-term migration are available as flows (the total number of moves made over a set period) and stocks (the number of short-term international migrants present or absent at a given point in time). It should be noted that a person could migrate more than once in the same period so the data are a count of migrant moves not individuals.

There are no estimates of short-term net migration flows as short-term migrants do not stay for more than 12 months and so do not become "usually resident". In addition, short-term migrants coming to England and Wales are counted in as short-term migrants but not out as short-term migrants, because to be counted out as a short-term migrant, a person needs to have been resident in England and Wales for 12 months or more. This means they are not included in population estimates.

Estimates of STIM are based on interviews on the IPS at the end of their stay capturing actual behaviour. Local authority estimates for STIM are produced for migrants who arrive in England and Wales for 3 to 12 months for work and study (which is the UN definition) by distributing IPS estimates to local authorities using administrative data.

Further information is available in the Short-Term International Migration estimates methodology.

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7. Other data sources that measure international migration

As well as the official statistics on long- and short-term international migration described in sections 5 and 6, which are largely based on the International Passenger Survey (IPS), there are also administrative datasets, which can provide information and often more detail on specific sub-groups of the population.

The Home Office Immigration statistics quarterly release provides data on visas, asylum seekers, voluntary and enforced removals, resettlement schemes and grants of citizenship.

Department for Work and Pensions provides data on the number of National Insurance number (NINo) allocations to adult overseas nationals entering the UK.

We also publish data on UK residents by country of birth and nationality as reported in the Annual Population Survey (APS). Residents may have recently arrived or been resident in the UK for a number of years and are a count of the stock of the non-UK population.

An overview of these data sources and how they can be compared is provided in Comparing sources of international migration statistics.

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8. When and where are migration data published?

Table 1: Summary of main international migration statistics

Publication When Measure Source
Migration Statistics Quarterly Report (MSQR) February, May, August and November Long-term international migration IPS, LTIM, Home Office, DWP
Immigration statistics quarterly report February, May, August and November Visa applications Home Office
National Insurance number (NINo) allocations to adult overseas nationals entering the UK February, May, August and November NINo registrations DWP
UK and non-UK people in the labour market February, May, August and November Labour market activity of migrants living in the UK (stocks) LFS
Population of the UK by country of birth and nationality May and November Number of migrants living in the UK (stocks) APS
Short-Term International Migration (STIM) May Short-term international migration IPS, Home Office
Local Area Migration Indicator Suite (LAMIS)

Migration levels: what do you know about your area?
August Migration in local areas IPS, Home Office, DWP, NISRA, NRS, PRDS
Annual International Passenger Survey (IPS) data tables November Long-term international migration IPS, LTIM


Source: Office for National Statistics
Notes:
  1. IPS (International Passenger Survey), LTIM (Long-Term International Migration), DWP (Department for Work and Pensions), LFS (Labour Force Survey), APS (Annual Population Survey), NISRA (Northern Ireland Statistics and Research Agency), NRS (National Records Scotland), PRDS (Patient Register Data Service).

In addition to these regular publications, you can find more ONS articles relating to international migration, covering topics such as the labour market, housing, the number of British migrants living abroad and ethnicity.

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9. How reliable are the Long-Term International Migration estimates?

Long-Term International Migration (LTIM) estimates are based primarily on data collected by the International Passenger Survey (IPS). Sample surveys like the IPS are used when we would like to know something about a population of individuals but asking all of them is impractical.

As with all sample surveys, the estimates produced are subject to variability because we did not ask the whole population their migration intentions.

Therefore, it is good statistical practice to publish confidence intervals around the estimates. A confidence interval is not a range in which any figure is equally likely, the most likely true figure is the estimate itself (Figure 2).

The published estimate 200,000 is the most likely figure in the range of plus or minus 30,000.

As well as being a measure of the reliability of the estimates, confidence intervals can be used to identify statistically significant changes. For further information on the reliability of our migration estimates, how to calculate confidence intervals and how to determine whether a change is statistically significant, please see Long-Term International Migration estimates methodology.

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Contact details for this Methodology

Nicola White
migstatsunit@ons.gsi.gov.uk
Telephone: +44 (0)1329 444097