1. Output information


 National Statistic   
 Survey name  International Passenger Survey (IPS)
 Frequency  Quarterly
 How compiled  Survey-based sample plus administrative data
 Geographic coverage  UK
 Related publications  Migration Statistics Quarterly Report (MSQR)

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2. About this Quality and Methodology Information report

This quality and methodology report contains information on the quality characteristics of the data (including the European Statistical System five dimensions of quality) as well as the methods used to create it.

The information in this report will help you to:

  • understand the strengths and limitations of the data

  • learn about existing users and uses of the data

  • reduce the risk of misusing data

  • help you to decide suitable uses for the data

  • understand the methods used to create the data

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3. Important points

  • 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 800,000 IPS interviews are conducted each year for migration purposes and of these between 3,000 and 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.

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4. Quality summary

Overview

Long Term International Migration (LTIM) estimates are the most comprehensive estimates of immigration, emigration and net migration flows to and from the UK. LTIM estimates are based on data from the International Passenger Survey (IPS) with adjustments made using administrative data.

Users and uses

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). 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.

As we set out at the Population and Public Policy forum in September 2017, the context for our work is changing. Users are telling us that they need more information on the impact migrants have while they are in the UK, including the sectors in which they work, the communities they live in and the impacts on public services such as the NHS and schools. Furthermore, there is a changing policy context, largely because of the UK exiting the EU; we therefore need to be able to inform decision-makers over the near-term, but also develop the data sources to ensure future policy and implementation are informed by robust evidence.

We therefore have plans to transform the information that the Government Statistical Service (GSS) produces on migration over the next two years to meet the changing user needs and which will begin to put administrative data at the core of evidence on migration in 2019.

Strengths and limitations

The International Passenger Survey (IPS) and the Long-Term International Migration (LTIM) estimates are currently the only sources of data to provide both total long-term immigration and emigration and so net migration estimates for the UK.

Other data sources measure different elements of international migration. While no single data source alone provides a full account of migration in the UK, collectively these sources provide useful evidence about international migration to and from the UK.

The IPS is a sample survey and as such provides estimates. When the estimates are broken down beyond the headline figures they are subject to greater levels of uncertainty.

The inherent limitations of the IPS sample survey approach to monitoring migration have been recognised for some time (for example, in the 2013 UK Statistics Authority report (PDF, 487KB)). Part two of our report on international migration data sources provides an update on the ongoing development of the IPS and details the independent data quality review carried out to ensure that the IPS data and the migration statistics produced are at the quality required.

Recent improvements

We have plans to transform the information that the Government Statistical Service (GSS) produces on migration over the next two years to meet the changing user needs, and which will begin to put administrative data at the core of evidence on migration in 2019. Part one of our report on international migration data sources provides an update on the exploratory research we have undertaken so far using Home Office administrative data.

Official assessments

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 former-student emigration estimate. 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 were “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 of 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 transformation 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.”

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5. Quality characteristics of the data

This section provides a range of information that describes the quality and characteristics of the data.

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:

  • relevance

  • timeliness and punctuality

  • coherence and comparability

  • accuracy and reliability

  • output quality

  • accessibility and clarity

Relevance

(The degree to which the statistical outputs meet current and potential users’ needs.)

Long-Term International Migration (LTIM) estimates 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 International Passenger Survey (IPS) data, because the characteristics of the other data sources used to calculate LTIM cannot be disaggregated to all IPS variables. The IPS 3 and 4-series tables, released each November, detail the additional data that are provided solely from the IPS.

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 United Nations (UN) definition of an international migrant for comparability.

Our traditional definitions of LTIM and Short-Term International Migration do not match the complexity of people’s lives and their movement between countries and the traditional definition of an international migrant is becoming less relevant. Government statisticians have been responding to these changing needs by collaborating and sharing data across government to improve the information that is currently available and we have set out our plans in a Transformation Work Programme.

Timeliness and punctuality

(Timeliness refers to the lapse of time between publication and the period to which the data refer. Punctuality refers to the lag between planned and actual publication dates.)

Provisional International Passenger Survey (IPS) and Long-Term International Migration (LTIM) data are released each quarter and from November 2014 are published five months after the reference period. For example, data for the year ending June 2015 were released in November 2015.

Final IPS calendar-year estimates are usually published in August. IPS estimates are less comprehensive than the LTIM figures, as they exclude the other adjustments but provide an early indication of how international migration is changing.

Final Home Office data on asylum seekers and non-asylum enforced removals for the reference year are usually not available until the July following the reference year. Final migration data from Northern Ireland Statistics and Research Agency (NISRA) are usually not available until the October following the reference year. Once these datasets are received the final LTIM estimates can be produced.

Final annual estimates (1, 2, 3 and 4 series reference tables) are released 11 months after the reference period, for example, estimates for 2014 were released in November 2015.

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 Statistics.

Accuracy and reliability

(Accuracy is the degree of closeness between an estimate and the true value the statistics were intended to measure.

Reliability is the closeness of the initial estimated value to subsequent estimated values.)

See the International Migration methodology report for more information on the accuracy and reliability of these data.

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 (PDF, 361KB) and the similar patterns seen across other data sources, such as visas issued to citizens outside the EU.

Since July 2018, the Migration Statistics Quarterly Report (MSQR) has presented the LTIM and IPS data with shading around the line on the charts to represent the uncertainty of the estimates due to the number of people surveyed, based on 30%, 60% and 95% confidence intervals. The line on the chart is the most likely value and the values towards the upper and lower band of the shading are possible but less likely.

Other sources of uncertainty are not represented, a few examples of this include: limitations of the survey methodology, potential misunderstandings of the questions, accuracy of interviewees’ answers and uncertainties caused by combining data from different sources.

Coherence and comparability

(Coherence measures the adequacy of the statistics to be combined in different ways and for various uses.

Comparability is a measurement of the impact of differences in applied statistical concepts, measurement tools and procedures where statistics are compared between geographical areas or over time.)

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 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, other countries may use different methods to measure long-term migration.

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 in the UK.

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. Users are advised to look at the timeline of methodological changes.

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.

Concepts and definitions

(Concepts and definitions describe the legislation governing the output as well as harmonisation principles and classifications used.)

We use the United Nations (UN) recommended definition of a long-term international migrant; these Recommendations on the Statistics of International Migration, Revision 1 UN Statistics Division 1998 are explained in detail on the UN website.

We use the Government Statistical Service (GSS) Harmonised Principles. The main terms and definitions used in our outputs can be found in the International migration – terms, definitions and frequently asked questions report.

Output quality

Independent Quality Review

In May 2018, a temporary processing system used during the implementation of the new data collection approach was found to contain an error that impacted on the IPS dataset; as a result, an in-depth independent review of IPS data quality has been completed.

Study adjustment

Because of the unusual pattern in student migration reported in July 2018, we produced an illustrative revised trend for the IPS non-EU student immigration estimate. For the year ending September 2016 estimates onwards we have taken the year-on-year percentage change in Home Office non-EU long-term student visa data and applied this rate of change to the IPS estimates for non-EU immigration for study. The illustrative revised trend shows a relatively stable pattern over this time period for IPS non-EU student immigration.

As non-EU student immigration feeds into overall immigration and net migration estimates, we have also produced illustrative revised trends for these estimates. These are for illustrative purposes only and we have not made any changes to the published IPS or LTIM figures. We plan to review this and consider whether a formal adjustment should be made.

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 recommended format for accessible content is HTML5 and/or PDF/A for narrative, charts and graphs.

Data should be provided in open, reusable and machine readable formats such as CSV and ODF.

An option to download or print the content should also be available.

More details on related releases can be found on the release calendar on GOV.UK. If there are any changes to the pre-announced release schedule, public attention will be drawn to the change and the reasons for the change will be explained fully.

In addition to this Quality and Methodology report, Quality and Methods information is included in each Migration Statistics Quarterly Report.

International Passenger Survey (IPS) estimates of international migration are available from the ONS website from 1975 and from 1964 to 1974 in paper publications. Further details and advice are obtainable from the Centre for International Migration, who can be contacted by email: migstatsunit@ons.gov.uk.

There is more information regarding conditions of access to data in:

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6. Methods used to produce the data

The Long-Term International Migration methodology report summarises:

  • how data are collected

  • data sources

  • current methodology

  • assumptions

  • timeline of methodological changes

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