|Survey name||International Passenger Survey|
|How compiled||Sample based survey|
|Last revised||24 August 2017|
Long-Term International Migration (LTIM) statistics estimate the flows and characteristics of migrants to and from the UK.
We define a long-term international migrant (applying the UN definition) as someone who changes his or her country of usual residence for a period of at least a year, so that the country of destination effectively becomes the country of usual residence.
LTIM estimates are based on data from the International Passenger Survey (IPS), which is a sample survey, with adjustments made for asylum seekers, resettlement schemes, switchers and flows to and from Northern Ireland; 95% confidence intervals are published alongside each estimate.
Approximately 700,000 IPS interviews are conducted each year for migration purposes and of these around 4,000 interviewees are identified as long-term international migrants.
Given the sample size many variables can only be disaggregated to a certain level before being subject to unacceptable margins of error, for example, migration from individual countries by single year.
IPS estimates of international migration are available online from 1975 and from 1964 to 1974 in paper publications; more comprehensive LTIM estimates (based primarily on the IPS, but supplemented with data from other sources), are available from 1991.
Long-Term International Migration (LTIM) is the most comprehensive estimate of long-term migration and produces flow measurements of immigration, emigration and net migration (the difference between immigration and emigration). There is no compulsory system to record international migration to and from the UK aside from for non-EU immigration, which is recorded in visa data.
There is no single, all-inclusive system for measuring LTIM. Therefore, it is necessary to use a combination of different sources that have different characteristics and attributes in order to produce international migration estimates.
These statistics are used both nationally and internationally, by government, academia, special interest groups, the media and the general public. International migration is also an important component of population change and is used in the production of population projections and mid-year population estimates, which are used by central and local government and the health sector for planning and monitoring service delivery, resource allocation and managing the economy.
There are many sources of official statistics that measure the number and characteristics of international migration into and out of the UK (flows) as well as the migrants who have settled in the UK (stocks). Taken together they provide a rich picture of migration in the UK. It is important to understand that these sources measure different things: some measure flows, some measure stocks, some measure workers, some students and some only measure the characteristics of those migrating from outside the EU. Each source is valuable in its own right in measuring particular aspects of international migration.
On 27 July 2017, the Office for Statistics Regulation (OSR) published their report on The quality of the long-term student migration statistics following a range of concerns that were raised about the robustness of the estimate of former-student emigration. The main focus of their report was the “student migration gap” – the difference between the estimate of the number of migrants entering the UK for formal study (student immigration) and the estimate of the number of former students leaving the UK (former-student emigration).
The estimate of former-student emigration is the only source of information about when a student leaves the UK. As a result, OSR was, “concerned that the former-student emigration estimate does not bear the weight that is put on it in public debate. This estimate should add clarity on the pattern of student migration in the UK. Instead, it creates doubts by not providing a complete and coherent picture of former-student emigration, as these figures alone do not provide information on all the different outcomes for international students”.
OSR set out several requirements for Office for National Statistics (ONS), one being to make clearer that this estimate should be treated with caution and that it be labelled as an experimental component of the overall National Statistics on migration, while the ONS work programme continues. OSR noted that, “It is standard practice for new figures to be labelled as experimental while they bed in and it is unfortunate that this was not followed in this case when the new breakdown of emigration figures by previous reason for immigration was first introduced.”Back to table of contents
This report provides a range of information that describes the quality of the output and details any points that should be noted when using the output.
We have developed Guidelines for Measuring Statistical Quality based on the five European Statistical System (ESS) Quality Dimensions. This report addresses the quality dimensions and important quality characteristics, which are:
timeliness and punctuality
coherence and comparability
output quality trade-offs
assessment of user needs and perceptions
accessibility and clarity
(The degree to which the statistical outputs meet users’ needs.)
We define a long-term international migrant as someone who changes his or her country of usual residence for a period of at least a year, so that the country of destination effectively becomes the country of usual residence. This is consistent with the UN definition of an international migrant. Long-Term International Migration (LTIM) statistics estimate the flows and characteristics of migrants to and from the UK. These statistics are used by government, academia, special interest groups, the media and the general public. International migration is also an important component of population change and is used in the production of population estimates and population projections.
There is no single, all-inclusive system for measuring LTIM. Therefore, it is necessary to use a combination of different sources that have different characteristics and attributes in order to produce international migration estimates. None of the data sources used, while offering the best data currently available, are specifically designed to capture information solely on LTIM.
LTIM (formerly total international migration (TIM)) is the most comprehensive estimate of long-term migration. It is based primarily on a subset of the International Passenger Survey (IPS), namely those international passengers sampled by the IPS who are migrants entering or leaving the UK by principal air, sea and tunnel routes. The IPS component is supplemented with the following adjustments:
Home Office administrative data, which are used to calculate an adjustment for asylum seekers and their dependants not counted by the IPS; for 2013 data onwards, administrative data on non-asylum enforced removals have also been included to adjust for those who have never claimed asylum but who are removed from the UK and who are not counted by the IPS; data on people who have resettled in the UK under various resettlement schemes are also included in the adjustment from 2015 onwards
an adjustment for visitor switchers (those who intend to enter, or leave, the UK for less than 12 months but will actually stay, or stay away, for longer) and migrant switchers (those who intend to enter, or leave, the UK for at least 12 months without those intentions being realised)
Quarterly National Household Survey data on flows to and from the Republic of Ireland provided by the Irish Central Statistics Office (1991 to 2007)
Northern Ireland Statistics and Research Agency (NISRA) data on migration to and from Northern Ireland (from 2008 onwards)
Statistics on international migration are available for a number of variables including citizenship, country of last or next residence, country of birth, age, sex, marital status, main reason for migration, usual occupation and area of destination or origin within the UK. Some detailed statistics can only be derived from IPS data, because the characteristics of the other data sources used to calculate LTIM cannot be disaggregated to all IPS variables. The IPS 3-series tables, released each November, detail the additional data that are provided from the IPS.
There is significant interest in migration statistics, both nationally and internationally, and there is a need to understand how moves impact on society and the economy. Migration estimates are a fundamental component of our mid-year estimates. These are used by central and local government and the health sector for planning and monitoring service delivery, resource allocation and managing the economy.
Timeliness and punctuality
(Timeliness refers to the lapse of time between publication and the period to which the data refer. Punctuality refers to the gap between planned and actual publication dates.)
Provisional IPS and LTIM data are released each quarter, and from November 2014 are published 5 months after the reference period. For example, data for the year ending June 2015 was released in November 2015. Final estimates (1, 2 and 3 series datasets) are released 11 months after the reference period, for example, estimates for 2014 were released in November 2015. However, final IPS calendar-year estimates are published usually in August. Home Office data on asylum seekers and non-asylum enforced removals for the reference year are not usually available until the July following the reference year. Migration data from NISRA are usually not available until the October following the reference year.
IPS estimates are less comprehensive than the LTIM figures, as they exclude the other adjustments described in the Relevance section, but provide an early indication of how international migration is changing. More detailed provisional LTIM estimates are published alongside the provisional IPS data and are broken down by citizenship and reason for migration.
There are more details on related releases in the GOV.UK release calendar, which provides 12 months’ advance notice of release dates. We will also notify you if there are any changes to the pre-announced release schedule and provide the reasons for the change, as set out in the Code of Practice for Official Statistics.Back to table of contents
International migration is made up of a number of components, which have changed over time.
Long-Term International Migration (LTIM) equals:
International Passenger Survey (IPS) flows plus Northern Ireland migration flows plus visitor switcher flows plus asylum seeker flows (including non-asylum enforced removals and people resettled in the UK under various resettlement schemes) minus migrant switcher flows
2013 to 2014
IPS flows plus Northern Ireland migration flows plus visitor switcher flows plus asylum seekers (including non-asylum enforced removals adjustment) minus migrant switcher flows
2008 to 2012
IPS flows plus Northern Ireland migration flows plus visitor switcher flows plus asylum seekers minus migrant switcher flows
1991 to 2007
IPS flows plus Republic of Ireland migration flows plus visitor switcher flows plus asylum seekers minus migrant switcher flows
Long-Term International Migration estimates methodology provides an overview of the current methodology. The change in calculating LTIM relating to processing of Republic of Ireland and Northern Ireland flows is outlined in the Accuracy section.Back to table of contents
(The degree of closeness between an estimate and the true value.)
The International Passenger Survey (IPS) provides reliable data on international migration at the national level. This is supported by the small (0.8%) difference between the 2001 to 2011 population estimates and the 2011 Census and the similar patterns seen across other data sources, such as visas issued to citizens outside the EU.
One aspect of measuring accuracy is sampling variability. As with all surveys, IPS is subject to sampling variability. If many samples were drawn, each set of estimates would vary slightly. Approximately 800,000 passengers are screened for migration. For example, during some shifts at Heathrow, every 30th passenger might be selected for the full IPS questionnaire, but every 10th person is screened for migration. If the person is a migrant, they are asked the migration questions, but if they are not a migrant they are asked no further questions (unless they also happen to be the 30th person).
Since international migration estimates are based on a small number of interviews (around 4,000 long-term migrants are identified by the IPS each year), many variables can only be disaggregated to a certain level before being subject to unacceptable margins of error, for example, migration from individual countries by single year. Previous publications have used standard error expressed as a percentage to indicate the reliability of IPS estimates. This could only usefully be done for inflow and outflow estimates. Therefore, since August 2012, the 95% confidence intervals have been used for all IPS estimates – inflow, outflow and net flow. This is the range within which is the true value of population parameters with known probability.
For example, the 95% confidence interval represents the range in which, over many repeats of the sample under the same conditions, we would expect the confidence interval to contain the true value 95 times out of 100. In other words there would be a 1 in 20 chance that the true value would be outside of the range of the 95% confidence interval. You are advised to be cautious when making inferences from estimates with large confidence intervals. Confidence intervals have been calculated using 1.96 multiplied by the standard error.
Confidence intervals are published as an indicator of accuracy. However, these confidence intervals have some limitations as they are designed for the IPS as a whole and not specifically for the subset of IPS migrants. Confidence intervals based on the IPS component of the estimate are shown for Long-Term International Migration (LTIM) estimates, but you should be aware that there is no method for quantifying the error associated with the non-survey components of LTIM and these errors are unlikely to be random. The IPS comprises around 90% of the total LTIM estimate and is the only contributory source susceptible to measurable sampling error. Similarly, the reporting of statistically significant changes to LTIM figures are based on the sampling error associated with the IPS component of these estimates.
The IPS confidence intervals do not take account of non-sampling errors. Examples of non-sampling errors include non-response bias and measurement error. Non-response bias would be introduced if those who choose to respond to the survey have different characteristics to those who do not; or, if sampled passengers do not complete an IPS questionnaire because the number of interviewers is insufficient to cope with the volume of passengers. The weighting applied to the estimates on total passenger flows will account for these non-contacts, but if their migration characteristics are different in some way then non-response bias would occur. Measurement error would be introduced, for example, if respondents provide incorrect information to the IPS interviewers.
The Migration Statistics Quarterly Report: Information for Users has further information on confidence intervals.
There are known issues with interviewees not being able to provide precise information. For example, immigrants stating an intention to reside in London may well stay there for only a very short time before moving to another part of the UK. The Labour Force Survey (LFS) provides more reliable data on the regional distribution of immigrants than the IPS, as it is based on where migrants actually live rather than on their initial intentions. However, the total IPS inflows are better for estimating the total inflow of migrants coming from abroad. A methodology (known as “calibration”) has been developed that redistributes the IPS data to the regional distributions in the LFS.
The Home Office data, which are used to calculate the asylum seeker and non-asylum enforced removals adjustment, are a high-quality source on asylum applications, refusals, forced and voluntary returns and withdrawals for principal applicants and their dependants, and appeals, as well as enforced removals of long-term migrants who have never claimed asylum. However, the data for asylum seekers do not correspond directly to the standard UN definition of a long-term international migrant. Broad assumptions must be made about the proportion of asylum seeker applicants that actually correspond to the UN definition. More recently, administrative data have been added to include people resettled within the UK, an assumption that mirrors asylum seeker inflows. Information on the assumptions made can be found within section 2 of the Long-Term International Migration estimates methodology.
One of the important features of IPS long-term migration data is that they are intentions-based. IPS long-term migrants are those who state an intention to change their country of residence for at least a year. However, it is known that these intentions are not always realised. Some people entering or leaving the country intending to be visitors (that is, staying or being away for less than 12 months) will actually migrate for more than a year and are called visitor switchers. For these to be incorporated into a more comprehensive estimate of migration, they must be added to the IPS migration estimates. Also, some people entering or leaving the country intending to migrate (that is, staying or being away for more than 12 months) will actually stay or leave the country for less than a year. These people are known as migrant switchers and need to be removed from IPS migrant flows.
Existing questions in the IPS are regularly reviewed and most years new questions are added to explore new areas of interest. All new questions proposed for the IPS are piloted before they are added to the survey and then agreed at the IPS Steering Group consisting of representatives from Office for National Statistics (ONS), government departments and stakeholders. The purpose of the pilot is to test the suitability and understanding of the questions, their positioning within the questionnaire, the appropriateness of question wording and any impact on response rates, the length and balance of the survey. The pilot locations are chosen to ensure that the questions can be adequately assessed on relevant passengers; respondents are purposely selected to ensure questions are appropriately tested; and the interviewers are fully briefed.
In 2004, new IPS questions were introduced to identify both migrant switchers and visitor switchers. For example, emigrants leaving the UK after being resident for a year or more were now asked how long they intended to stay when they initially arrived. Those who initially intended to stay for less than a year were flagged as former visitor switchers. Similarly, migrant switchers were identified by using these same questions and estimates of visitor and migrant switchers are now made by using this method. Details of the visitor and migrant switcher methodology can be found in the Long-Term International Migration estimates methodology.
In 2012, we introduced a question asking people emigrating from the UK what they previously immigrated for (that is, work or study).
When the “previous reason for migration” questions were piloted, seven new questions and two revisions were proposed for testing at that time. It was found that interviewers did not have any problems administering the new questions or the revisions to existing ones. Respondents generally understood the questions as intended and provided the required information. The pilot identified a routing issue, which was easily solved by removing a code from the routing instructions. Therefore in 2012, the new questions were added to the IPS and data from these new questions for the year ending December 2012 were published for the first time in August 2013, showing outflow of migrants by citizenship and, for former immigrants, previous main reason for immigration.
We have published International Passenger Survey Quality Information in Relation to Migration Flows, which provides an overview of the quality and reliability of the IPS in relation to producing estimates of long-term migration flows.
Between 1991 and 2007, we used data from the Central Statistics Office (CSO) in the Republic of Ireland to estimate migration flows between the UK and the Republic of Ireland. Their data were used because there were no routes between the two countries surveyed by the IPS. However, evidence suggests that the CSO estimates of flows from the Republic of Ireland to the UK were underestimated. Although IPS flows have not been used in the past, the data have in fact been captured on routes between the UK and the Republic of Ireland since 1999. We have been monitoring these flows and comparing both sources of data and now consider the IPS to be the better source. As a result we ceased using data from the CSO to measure international migration between the UK and Republic of Ireland from 2008 and started to use the IPS to measure these flows instead.
With any change in estimating migration to and from the Republic of Ireland, it is sensible to review the methodology for measuring international migration to and from Northern Ireland to ensure that migration over the land border is accounted for. Until 2007, different methods were used by us and Northern Ireland Statistics and Research Agency (NISRA) to estimate international migration to and from Northern Ireland. We now use the health-card estimates already used by NISRA. Health-card data contain records for individuals who were previously resident outside the UK and register with a GP in Northern Ireland. We will use the best data source available and ensure consistency for users.
These adjustments are necessary to produce a more comprehensive estimate of international migration.
Coherence and comparability
(Coherence is the degree to which data that are derived from different sources or methods, but refer to the same topic, are similar. Comparability is the degree to which data can be compared over time and domain, for example, geographic level.)
Different countries operate within different regulatory and legislative frameworks that determine the broad approach taken to measuring migration. Countries that operate strict border controls usually use precise administrative data on migrant flows. Most European countries base their estimates on residence permits and/or population registers.
There is also a lack of consistency of fundamental concepts. Different countries, even within the EU, use different definitions of what constitutes a migrant. We use the UN definition of a long-term international migrant, which is someone who changes their country of usual residence for a period of at least a year, so that the country of destination effectively becomes the country of usual residence. By contrast, Italian migration statistics are based on changes in country of usual residence of at least 3 months’ duration.
The European Commission regulation 862/2007 aims to harmonise definitions across Europe by ensuring that member states provide Eurostat with consistent statistics on migration, based on UN definitions, which the UK already uses.
There are additional data sources (administrative data and survey) available that may provide information on international migration. These sources are not specifically designed to measure international migration, but may serve as further references on the topic.
All sources of international migration statistics are valuable in their own right and provide us with an understanding of the flows of international migrants, as well as the numbers of international migrants in the household population. There are known differences between all the different data sources that measure international migration and several articles have been published to explain these differences.
On 12 May 2016, we published an information note on the reasons why LTIM figures from the IPS differ from National Insurance number (NINo) registrations, noting that short-term migration to the UK largely accounts for the recent differences. The IPS continues to be the best source of information for measuring LTIM and while NINo registrations data are not a good measure of LTIM, they do provide a valuable source of information to highlight emerging changes in patterns of migration.
On 1 December 2016, we published an information note on the differences between LTIM and Annual Population Survey (APS) estimates. The article explores the definitional differences between the two sources, accompanied by some illustrative analyses. The analyses show why deriving a proxy for a long-term international migration flow from the change in the annual APS population estimate is not advisable, as the calculated difference is not as reliable as the LTIM estimates of flow, which have lower variability and are directly designed to monitor migration flows. We also published a note on Comparing sources of international migration statistics relating to all the notes that have been published.
|Potential sources of migration data||Comparability with our estimates of international migration|
|Home Office – these figures include statistics on immigration, asylum, resettlement and nationality. The data available from the Home Office cover:
• passenger arrivals, admissions and refusals at air, sea and Channel Tunnel ports in the UK
|These provide a measure of longer-term immigration of persons subject to immigration control who are allowed to remain in the UK. However, the definition of settlement differs from that of migration used in the IPS.|
|Eurostat – Eurostat publish tables on international migration and asylum by:
• individual European country
|We supply Eurostat with IPS data for the following variables:
• residency by age
These are fed through with data supplied by other European countries to populate the Eurostat migration tables. Further information on consistency of migration statistics between other European countries is available from the Statistics Explained section of the Eurostat website.
|National Insurance number (NINo) – National Insurance number allocations are made by the Department for Work and Pensions (DWP) to overseas nationals entering the UK who wish to work or claim benefits in the UK.||This source does not capture movement of international migrants arriving to the UK for non-work purposes. These issues are discussed further in the DWP publication National Insurance number allocations to adult overseas nationals entering the UK.|
|United Nations – the United Nations Statistics Division (UNSD) collects and disseminates statistics on international migration flows and on the stock of migrant population through the Demographic Yearbook data collection system.||UNSD collects data from national statistical authorities using a set of questionnaires that are sent to over 230 national statistical offices. Further information on consistency of migration statistics between other countries is available from the International Migration Standards and Methods section of the UN website.|
|United Nations Economic Commission for Europe (UNECE) – the Population Activities Unit of UNECE disseminates basic demographic data on the countries of central and eastern Europe, including all the members of the Commonwealth of Independent States. Many western European countries are also included.||For migration, the Population Unit within UNECE produces the rate of net migration increase for these countries since 1982.|
Annual LTIM estimates from 1991 onwards can be directly compared with one another. However, annual estimates before 1991 use a different methodology and cannot be directly compared with more recent figures.
When looking at specific variables there are small discontinuities in the series since 1991. For example, the IPS alone was used to create the geographical distribution of international migration between 1991 and 1998, but since 1999 the Labour Force Survey (LFS) has been used to adjust the discrepancy between where respondents to the IPS stated they intended to live upon arrival in the UK and where they actually live.
Other discontinuities include questions that were introduced into the IPS from 2004 to get estimates of visitor and migrant switchers, which replaced the broad assumptions used to estimate these components before 2004. Also, from 2008, there were changes made to estimating migration between the UK and the Republic of Ireland, and to and from Northern Ireland.Back to table of contents
(Concepts and definitions describe the legislation governing the output and a description of the classifications used in the output.)
We use the UN recommended definition of a long-term international migrant (the Relevance section has further details); these Recommendations on the Statistics of International Migration, Revision 1 UN Statistics Division 1998 are explained in detail on the UN website. This 12-month migrant definition is also used for the UK usually resident population estimate series.
There is also a summary of how the Long-Term International Migration (LTIM) estimates are calculated, LTIM Frequently Asked Questions and Background Notes, which also contains definitions and terms used in documentation.Back to table of contents
Output quality trade-offs
(Trade-offs are the extent to which different dimensions of quality are balanced against each other.)
Provisional estimates provide a good early indication of recent migration trends. Final estimates take account of adjustments and updates to Civil Aviation Authority and the Department for Transport information, which are used to weight the observed data collected by the International Passenger Survey (IPS).
Additionally, the supplementary migration data used in the calculation of Long-Term International Migration (LTIM) may also have been updated between the release of provisional and final LTIM estimates.
The differences between the provisional and final estimates of the IPS and the provisional and final estimates of LTIM are minimal. For more information please refer to LTIM Frequently Asked Questions and Background Notes.
Assessment of user needs and perceptions
(The processes for finding out about uses and users, and their views on the statistical products.)
In January 2017, the Office for Statistics Regulation (OSR) published an assessment report covering Department for Work and Pensions (DWP) statistics on National Insurance number (NINo) allocations to adult overseas nationals and nationality at point of NINo registration of DWP working age benefit recipients (NINo benefit claimants), for compliance against the Code of Practice for Official Statistics. OSR judgement is that the statistics published should have their National Statistics status temporarily suspended until work to improve their limited supporting guidance and overall public value is undertaken. The full assessment can be found on the UK Statistics Authority website: Report on the reassessment of the NINo statistics.
Office for National Statistics (ONS) will continue to include statistics and commentary on NINo data pending further reviews with OSR this year.
In July 2014, the UK Statistics Authority confirmed that Migration Statistics had retained their National Statistics status, as detailed in the assessment report.
Also, in July 2009, the UK Statistics Authority reported on Migration Statistics: the Way Ahead?, and the recommendations can be found in their report.
In addition, the Public Administration Select Committee (PASC) published a report in July 2013 on Migration Statistics following a review conducted in April 2013.
Presentation of migration statistics
A consultation on international migration statistics outputs was held from 11 November until 23 December 2016 to gather insight and seek user views on the presentation and timing of the published international migration statistics outputs, specifically which outputs are used, why and what other data sources users would like to see published.
ONS will move to shorter more streamlined Migration Statistics Quarterly Report (MSQR) publications in 2017. We will also work to redesign the MSQR and migration products to meet user needs of developing a more coherent story of international migration in the UK. Regardless of future changes all the data previously published in the MSQR will still be made available for users to download and explore.
A previous consultation ran from 20 June 2014 to 18 July 2014 on The reporting of International Migration Statistics. The main findings were:
a shortened MSQR implemented for the November 2014 MSQR
to include more information on the reliability of migration estimates and a clearer explanation of confidence intervals and statistically significant changes
overall, there were some clear differences in user needs, suggesting that a suite of products, which can support the main bulletin, is needed; users also requested a single web page which could provide links to all migration-related data
The consultation on country groupings ran from 21 January 2014 to 18 March 2014. As a result of the consultation we now produce our quarterly International Passenger Survey (IPS) data tables to the new country groupings and in November 2015 we extended our 3-series tables to include data for the new country groupings. As of February 2016 we now include new country groupings in the 2-series tables too.
A previous consultation on international migration statistical outputs took place in 2012.
The main outcomes of this 2012 consultation were:
population by nationality and country of birth tables will no longer be updated quarterly, but will be published annually in August, to include figures referring to the previous calendar year
local area migration indicators will no longer be updated quarterly, but will be published annually in August
we should continue to publish quarterly data on international migration flows and the MSQR
Accessibility and clarity
(Accessibility is the ease with which users are able to access the data, also reflecting the format in which the data are available and the availability of supporting information. Clarity refers to the quality and sufficiency of the release details, illustrations and accompanying advice.)
The international migration data and supporting information are available.
International Passenger Survey (IPS) estimates of international migration are available online from 1975 and from 1964 to 1974 in paper publications. Further details and advice are obtainable from the Migration Statistics Unit, who can be contacted by email: firstname.lastname@example.org.
Our recommended format for accessible content is a combination of HTML web pages for narrative, charts and graphs, with data being provided in usable formats such as CSV and Excel. Our website also offers users the option to download the narrative in PDF format. In some instances other software may be used, or may be available on request. For further information please contact: email@example.com.
There is more information regarding conditions of access to data in:Back to table of contents