Long-Term International Migration QMI

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

• 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 and preliminary adjustments to account for uncertain intentions.

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

• We are currently transforming the way we produce population and migration statistics. Whilst we go through this transformation journey, we have sought to re-classify our migration statistics as “Experimental Statistics” in line with Office for Statistics Regulation guidance.

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.

It is our mission to provide the best insights on population and migration using a range of new and existing data sources to meet the needs of our users. This is increasingly important in a rapidly changing policy context, where we know our users need better evidence to support decision-making at both national and local levels. We are therefore transforming our population and migration statistics to put admin data at the core of what we do.

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.

However, it has long been acknowledged that the IPS, which underpins our existing international migration estimates, has been stretched beyond its original purpose and that we need to consider all available sources to fully understand international migration. Our latest research sets out how we can draw on the combined strengths of survey and administrative sources to provide a better understanding of international migration.

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 are transforming the information that the Government Statistical Service (GSS) produces on migration. We have set an ambitious target to put administrative data at the core of our evidence on international migration by 2020.

As part of this work, research has clearly shown that no single source of data can fully reflect the complexity of migration. However, when we look at all available sources together it provides a much clearer picture. We set out how we can draw on the combined strengths of survey and administrative data to provide a better understanding of international migration in Understanding different migration data sources: August 2019 progress report.

Bringing these research findings and all available data sources together, from August 2019, we have made preliminary adjustments to our previously published headline measures of migration. This is to provide our best possible assessment of trends over time.

As new data sources become available, we will build on our research so far and continue to develop our approach for adjusting IPS estimates to take account of uncertain intentions.

Official assessments

On 21 August 2019, the Office for National Statistics (ONS) wrote to Ed Humpherson, Director General for Regulation at the UK Statistics Authority, to request support for the reclassification of the Migration Statistics Quarterly Report (MSQR) as Experimental Statistics. In response Ed Humpherson confirmed that the Authority has concluded that the MSQR should not be designated as National Statistics.

We have been transforming our migration statistics, making use of all available data to get a richer and deeper understanding on migration since 2017. This work has involved departments across government to harness the power of new data sources following the passing of the Digital Economy Act 2017.

To date this picture was mainly based on the International Passenger Survey (IPS) and the ONS has been clear about its limitations. It is an intentions-based survey and there is evidence that there are some groups for both EU and non-EU citizens with uncertain intentions who are not well captured by the IPS.

Based on these findings we have made preliminary adjustments based on data sources from the Home Office and Department for Work and Pensions, which tell us about migrants’ actual behaviour. These are giving us the best assessment yet of migration trends over time.

We have confidence in our overall assessment of migration trends, but recognise that development will be ongoing as we look to more data sources. Therefore whilst we go through this transformation journey, we have sought to re-classify our migration statistics as “Experimental Statistics” in line with Office for Statistics Regulation guidance.

We expect our current work programme to be complete by August 2020 when we will seek re-designation to National Statistics status.

Other 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).

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.

Between July 2018 and June 2019, the Migration Statistics Quarterly Report (MSQR) presented the LTIM and IPS data with shading around the line on the charts to represent the uncertainty of the estimates because of 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. From August 2019 we no longer present confidence intervals around adjusted estimates that have the preliminary adjustment applied to them. We are working to produce confidence intervals for estimates adjusted using admin data in the future.

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.

Currently, only some LTIM estimates have had the preliminary adjustments applied to them, others remain unadjusted. Over the next year we are working to finalise the adjustments and will look to apply them to all our LTIM estimates.

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

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. We have now made a revision to the IPS and LTIM estimate for non-EU formal study immigration for the year ending September 2016, which forms part of the subsequent estimates for three rolling years. A guidance note has been published to explain the revision. The revision affects estimates for the years ending September 2016, December 2016, March 2017 and June 2017. As non-EU student immigration feeds into overall immigration and net migration estimates, we have also produced revised estimates for these figures.

Revised estimates are highlighted in the accompanying dataset and presented without confidence intervals as it is not possible to quantify the uncertainty associated with them. The original estimates are available in earlier publications of the accompanying dataset.

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.

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:

• terms and conditions (for data on the website)

• accessibility

The Long-Term International Migration methodology report summarises:

• how data are collected

• data sources

• current methodology

• assumptions

• timeline of methodological changes