1. What has been released and where can I find it?

1.1 Which are the latest available migration estimates?

The latest estimates released on 24 August 2017 are for the year ending March 2017. These are detailed provisional estimates for Long-Term International Migration (LTIM) for 2016 and 2017, alongside final estimates from the International Passenger Survey (IPS) for 2016.

Final LTIM are available each November or December for the previous calendar year (and mid-year). The latest final estimates available are for 2015.

1.2 What long-term international migration estimates are available?

There are two types of estimates on long-term international migration flows that are published on a regular basis:

  • long-term international migration from the International Passenger Survey (IPS) – these are the IPS tables

  • Long-Term International Migration (LTIM) – these are the LTIM tables

All tables can be linked to from the Table of Contents.

The two sets of estimates cannot easily be compared and should not be confused. Users need to be aware of which set of tables they are using. For more information on the difference between LTIM and IPS estimates see Section 3 on methods and coverage.

Provisional and final estimates are produced for each type of long-term international migration flow data. Provisional estimates give a timely indication of the flow levels of international migration, being produced 5 months after the reference date, compared with 11 months for final data.

Provisional IPS (rolling year quarterly)

These estimates are based solely on data collected by the IPS. They offer an early indication of changes in patterns of long-term international migration to and from the UK. The rolling year-based estimates are produced every quarter and provide up-to-date data on citizenship and main reason for migration and are available for the last 10 years.

Provisional LTIM (rolling year quarterly)

Estimates of LTIM are about 90% based on data from the IPS. In addition they are adjusted to account for asylum seekers (including a non-asylum enforced removals adjustment and people resettled in the UK under various resettlement schemes), migration to and from Northern Ireland and people whose length of stay changes from their original intentions. They offer the most comprehensive early indication of migration flows into and out of the UK.

Releases of provisional LTIM data every quarter show overall estimates of immigration, emigration, and net migration by citizenship and main reason for migration, and are available for the last 10 years.

Final IPS calendar year (3-series and 4-series)

These estimates are published annually in November or December. They provide detailed cross-tabulated data of all available variables. Since November 2012, the data within the 3-series tables have been available from 1975 onwards (superseding the 2-series tables previously published covering 1975 to 1990).

Characteristics of migrants that are in one or more of the tables are: citizenship, country of last or next residence, country of birth, age and sex, sex and marital status, usual occupation (prior to migration), main reason for migration, previous main reason for migration, origin or destination within the UK, intended length of stay, actual length of stay and route.

4-series tables are underlying datasets of final IPS data. These annual tables provide further breakdowns of migrant characteristics by individual country rather than country grouping. Underlying datasets are available from 2000 to the latest annual estimates (2015).

Final LTIM calendar year (1-series and 2-series)

LTIM estimates provide the most comprehensive estimates of long-term international migration to and from the UK. The IPS provides the foundation of these estimates. Final LTIM estimates are published annually in November or December. Data are available from 1991 and include tables by calendar year, half year or mid-year.

2-series tables usually focus on one characteristic of migrants, from the following list: citizenship, country of last or next residence, country of birth, age and sex, sex and marital status, usual occupation (prior to migration), main reason for migration, origin or destination within the UK and intended length of stay.

1-series (methodology) contains tables showing the components and adjustments for LTIM and the confidence intervals and non-response associated with the IPS estimates. These are available from 1975 onwards.

For a comprehensive list of all published tables and variables please see Section 6 and for links to all tables, please see our Table of Contents.

1.3 What is the difference between provisional and final data?

Provisional figures allow for a timely comparison of recent migration patterns on a quarterly basis. However, these are subject to change as their calculation is based upon provisional data. The final LTIM estimates are considered to provide a more reliable picture of migration and allow for annual comparisons over time.

For more information see MSQR Information for Users.

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3. Methods and coverage

3.1 How are estimates of Long-Term International Migration (LTIM) calculated?

3.1.1 Data sources

There is not a single, all-inclusive system in place to measure all movements of migrants into and out of the UK. Therefore, it is necessary to use a combination of data from different sources that have different characteristics and attributes in order to produce estimates of LTIM. None of the data sources used, while offering the best data currently available, are specifically designed to capture information solely on LTIM.

The sources of data used are:

  • the International Passenger Survey (IPS), a voluntary sample-based survey; is the prime source of long-term migration data providing estimates of both inflows and outflows, but does not cover all migration types

  • Labour Force Survey (LFS) – provides a geographical distribution of long-term immigrants for the calibration of IPS inflow data

  • Home Office immigration administrative systems; which provide data on asylum seekers and their dependants for 1991 onwards; from 2013, data on non-asylum enforced removals are also used and from 2015, adjustments for people resettled in the UK under various resettlement schemes

  • forecasted long-term international migration estimates based on previous GP registrations from the Northern Ireland Statistics and Research Agency (NISRA) for estimating long-term international migration to and from Northern Ireland and the rest of the world, from 2008 onwards (forecasted data is replaced with final data for LTIM final annual estimates)

3.1.2 Long-Term International Migration (LTIM) tables of estimates

The IPS accounts for about 90% of LTIM estimates. It has some limitations with respect to measuring immigration and emigration, as it:

  • is a sample survey and so the estimates are subject to a degree of uncertainty

  • captures very few asylum seekers who may be entering or leaving the UK, or non-asylum enforced removals from the UK

  • does not take into account the changing intentions of passengers; these are passengers who intended to remain in or out of the UK for 12 months, but actually spent less than a year (migrant switchers) and those who believed they would be staying or leaving for less than a year but actually spent longer (visitor switchers)

  • does not capture those who are crossing the land border between the UK (Northern Ireland) and the Republic of Ireland

A more comprehensive estimate of long-term international migration is produced by combining the IPS data with the information provided by the additional sources listed in Section 3.1.1 Adjustments are also made for migrants who change their intentions, known as visitor and migrant switchers. This more inclusive estimate is referred to as Long-Term International Migration (LTIM).

Data received from these supplementary sources are not as detailed as the data collected by the IPS, which limits the level of analysis that can be performed on the LTIM data. While LTIM tables usually contain just one variable, cross-tabulations of IPS data are available in the IPS 3-Series Tables.

Further information on the methodology to produce IPS and LTIM estimates (Methodology to estimate LTIM), including changes to the methodology over time, is available. This also includes copies of the questionnaires used in the IPS.

3.2 What about those migrants who stay less than a year?

Long-Term International Migration (LTIM) estimates do not include estimates of short-term migrants. The LTIM estimates use the recommended definition of an international long-term migrant (see Section 5.1). UK population estimates do not currently include short-term immigrants as usually resident in the UK, nor do they exclude short-term emigrants from the usually resident population.

In May 2017, Office for National Statistics (ONS) released the Short-Term International Migration Annual Report (STIMAR) for England and Wales, for mid-2015. The STIMAR includes estimates of short-term immigration and emigration to and from England and Wales for periods of 1 to 12 months, 3 to 12 months and 3 to 12 months for work or study on the basis of the UN definition of a short-term migrant. Local authority-level estimates of immigration for England and Wales are also produced on the basis of the UN definition.

For more information about Short-Term International Migration estimates, please refer to the Short-Term International Migration Frequently Asked Questions.

3.3 How can I find out about long-term international migration in my local area?

Final International Passenger Survey (IPS) and Long-Term International Migration (LTIM) estimates of long-term international migration are available for the countries of Great Britain and the regions of England. Final LTIM estimates also provide separate estimates for Northern Ireland.

National and regional migration flows are disaggregated to local area level in order to produce mid-year population estimates by local authority. The Population Estimates Analysis Tool can be used to investigate population change, including migration into and from each local authority.

To compare Office for National Statistics (ONS) estimates with other sources of migration data at local area level, please use the Local Area Migration Indicators Suite.

Further data from the 2011 Census are available.

3.4 How can I find out any information on non-UK born or non-British residents living in my area

Estimates based on the Annual Population Survey (APS), which is the Labour Force Survey (LFS) plus various sample boosts, are published annually, providing information on the Population by country of birth and nationality. These estimates of countries of birth and nationality by region and non-UK can be split down to the local authority level.

The main published tables are also accompanied by datasets, supplying lower level detail on individual countries of birth and nationality.

Additionally, in May 2013, we released detailed country of birth and nationality analysis from the 2011 Census of England and Wales.

In November 2014, we released a report on 2011 Census analysis: Social and Economic Characteristics by Length of Residence of Migrant Populations in England and Wales.

In April 2017, we published a report on International immigration and the labour market, UK: 2016.

Future development plans for improving our data sources are outlined in an article published in February 2017: International migration data and analysis: Improving the evidence.

Released in May 2017, International migration and the changing nature of housing in England – what does the available evidence show? provides information about international migration, population change and changes in housing trends in England.

3.5 Is there any information about international migrants’ ethnicity available?

The International Passenger Survey (IPS) collects information on individuals’ citizenship, but not specifically on ethnicity.

There are other data sources available for ethnicity but these data do not relate specifically to migrants.

The Labour Force Survey provides detailed Labour market status by ethnicity for regional and local areas.

Data on ethnicity from the 2011 Census of England and Wales are available.

3.6 Is it possible to sum together the Long-Term International Migration (LTIM) data and population figures for resident foreigners in the UK, for a single year, to get the following year’s foreign population estimate?

No, not for long-term migration, that is for migration longer than a 12-month period. This is mainly because of the definitional differences between the two surveys used to estimate migrant flows (IPS) and the foreign resident population (Annual Population Survey (APS)).

A recent discussion on the differences between international migration data from the Labour force survey (LFS) and APS, and IPS and LTIM can be found in the report published 1 December 2016: Note on the differences between Long-Term International Migration flows derived from the International Passenger Survey and estimates of the population obtained from the Annual Population Survey.

3.7 Do you have data on the numbers of UK migrants living abroad?

A report was published in January 2017, which explored statistics available to estimate the number of British migrants living in Europe. There will be a further series of reports published within the next year to update this report, focusing firstly on Spain, followed by EU8, France, EU2, Ireland, Germany, Mediterranean countries and northern Europe.

Alternatively, an individual country breakdown for Europe can be found on the Eurostat website. The US Census Bureau website contains a list of International Statistical Agencies.

3.8 Is it possible to produce an accurate figure for the number of people who are in the country illegally?

The London School of Economics1 identified three main categories of illegal or “irregular” migrants, which include:

  • illegal entrants – including both those who evade formal migration controls and those who present false papers

  • migrants who have been lawfully present in the country but remain after the end of the permitted period (two main subcategories):

    • failed asylum seekers who stay in the country despite a final decision refusing them continuing right to remain
    • overstayers whose period of legal residence has expired without renewal: this group includes those who are no longer eligible to apply for extensions because of the introduction of the points system
  • children born in the UK to irregular migrant couples; they are not migrants themselves, but have no right to remain

By its very nature it is impossible to quantify accurately the number of people who are in the country illegally. For this reason Office for National Statistics (ONS) do not produce estimates on the size of the illegal migrant population. However, while our data do not identify illegal migrants separately, many will be included in our data. Those who overstay their visa would have been counted in our immigration figures by the International Passenger Survey (IPS) when they originally entered the country and those who arrived illegally and then subsequently claimed asylum will also be included.

Furthermore, every 10 years ONS conduct the census and at this time a notable proportion of the illegal migrant population should be captured in the population estimates. The 2011 Census initially captured 94% of the resident population using an address register and focusing on hard-to-count areas. Adjustments were then made following the Census Coverage Survey to estimate the whole population.

In June 2005, the Home Office published the outcome of an assessment of whether methods used in other countries to estimate the size of the illegal population could be applied to the UK. The outcome estimated that the total unauthorised migrant population living in the UK in 2001 was 430,000. Please see the following reports for more information: 29/05 - Sizing the unauthorised (illegal) migrant population in the United Kingdom and 58/04 - Sizing the illegally resident population in the UK. As mentioned previously, a report written by the London School of Economics1 estimated that in 2007 the number of “irregular” migrants was 618,000 (which includes all of the above listed main categories)2.

3.9 Why do estimates of long-term international migration differ from the number of National Insurance numbers allocated?

On 12 May 2016, we published an information note explaining the reasons why long-term international immigration figures from the International Passenger Survey (IPS) could differ from the number of National Insurance number (NINo) registrations. It noted that the two series are likely to differ because of short-term immigration, definitional differences between the data sources and timing differences between arriving in the UK and registering for a NINo. Definitional differences between these data are fundamental and it is not possible to provide an accounting type reconciliation that simply “adds” and “subtracts” different elements of the NINo registrations to match the Long-Term International Migration (LTIM) and Short-Term International Migration (STIM) definitions.

The analysis used 1 to 12 month short-term migration estimates for employment, study and work (other) to help explain the gap as this group was most likely to contain people who might register for a NINo. In year ending June 2015 there were 290,000 EU citizens immigrating to England and Wales for 1 to 12 months for the reason of employment, study or work (other) compared with 251,000 the previous year. This is not the total level of STIM but the most appropriate to help explain the gap.

Adding together LTIM and STIM estimates does not provide a reliable measure of all immigration to the UK within a specific time period. Short-term immigration flows are based on journeys, not people and have methodological differences from LTIM flows. In addition, it is possible for someone to be both a long-term and short-term migrant in the same period and STIM estimates are based on actual flows whereas LTIM covers migrants' intentions.

However, although they cannot be added together to provide one single, accurate measure of international migration, LTIM and STIM estimates of immigration and emigration should be considered alongside and in the context of each other. These estimates represent different people immigrating for different reasons but they can help to provide an overall picture of international migration. Historical data on short-term and long-term international migrants is available, and there is a summary of the definitional differences between these data. For more detail on the NINo and IPS comparison, you are encouraged to read the report.

3.10 Why do IPS formal study estimates not match student visas figures?

The International Passenger Survey (IPS) formal study figures provide an estimate of the number of migrants indicating their main reason for migrating is to attend a formal study course in the UK. This may not match other measures of "student" immigration such as the number of student visas issued, for a number of reasons, such as:

  • IPS estimates only include those people who intend to stay for 12 months or more, whereas visas data include people coming to the UK for less than 12 months

  • the IPS category includes accompanied children, who are not included in the student visas figures

  • the IPS only records the stated main reason for entering the UK (this may not correspond with the nature of the visa they hold because they may also have other reasons for immigrating)

For further details please see Comparing sources of international migration statistics.

3.11 Why is there a decrease in the long-term IPS student estimates, which is not reflected in the number of student visas issued?

There is a notable difference between the long-term International Passenger Survey (IPS) figures for immigration to study and long-term student visa data for the year ending (YE) March 2017. There are potential reasons why the data sources differ such as: timing, stated intentions and length of stay, sampling variability and the fact that a visa may not be used. There have been differences in the trends between the IPS and visa data for study in the past, in particular around 2009 and 2010, so this is not unprecedented.

Long-term international student migration has a marked seasonal pattern with a large proportion of people immigrating to study in the July to September quarter, particularly for those who will start the academic year in September, so changes in immigration are more likely to be reflected in the YE September reporting year. It is too early to tell if this is an indication of an emerging long-term trend of the IPS student data as it is based on 3 quarters' data and a similar fall has not been seen in the number of study visas issued to non-EU citizens. Therefore we will continue to monitor the trends and compare against other sources, such as university admissions data. Our future work programme will also help to understand such differences - International migration data and analysis: Improving the evidence.

3.12 Can we use IPS formal study data to estimate the net balance of students entering and leaving the country?

Care should be taken when interpreting net migration estimates by main reason for migration and particularly for students. For example, a migrant who arrived in the UK to study may subsequently leave to take up a job abroad and so not be included in the estimate of net migration for formal study, which can be found in provisional International Passenger Survey (IPS) estimates of migration flows by citizenship and main reason for migration. These balance migration figures are the difference between the numbers of migrants arriving to study and the numbers of migrants leaving to study.

From January 2012, new questions were added to the IPS to ask those leaving the UK what their main reason for migrating was when they arrived. 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. Three final IPS 3-series tables, including the previous main reason for migration variable, were also published in November 2013. Caution should be exercised when comparing these new data with other IPS estimates of international migration, particularly when estimating net flows. A guidance note (International Migration – How to interpret Table 4) explains what the new data show and how they can be interpreted in relation to estimating the net balance of students entering and leaving the country.

Similarly, caution should be applied when considering the “student” usual occupation prior to migration. If, for example, a student has worked part-time before leaving the country, their prior occupation will be work-related.

3.13 Why is there a gap between the number of non-EU students arriving in the UK and the number leaving who originally came to study?

In 2012, a new question was added to the International Passenger Survey (IPS) asking current emigrants who had previously immigrated to the UK about their main reason for migration at the time that they arrived. The available information is reported on in the Migration Statistics Quarterly Report and its accompanying downloadable tables. This showed an apparent gap between the number of non-EU students arriving in the UK and the number leaving who originally came to the UK to study. However, further analysis of these data is ongoing to fully understand what the figures are showing and it is likely that more years of data will be needed for conclusions to be drawn.

An article was published in January 2016 that considers the impact of long-term international student migration with particular reference to the differences between the two sets of figures: Long-Term International Migration: International student migration – What do the statistics tell us? Updates to this article were published in November 2016 and April 2017 to better understand student migration to and from the UK.

Specifically looking at non-EU students some explanations could include:

  • non-EU students extending their visas to remain in the country longer

  • IPS respondents not recalling that they originally entered the UK as a student

  • sampling error of the IPS

  • some non-EU students remaining in the UK without a valid visa

  • some non-EU students granted British citizenship or settlement

  • timing – those migrants arriving as long-term international students will not leave until at least a year after arriving and often this will be several years later due to the length of their course

3.14 Why have the former student emigration estimates been labelled as experimental?

Recently, a range of concerns about the robustness of the estimate of former student emigration were raised with the Office for Statistics Regulation (OSR). As a result, OSR carried out a review of The quality of the long-term student migration statistics, which was published on 27 July 2017. OSR investigated a number of factors that determine the extent to which the IPS accurately captures long-term student migration, including the sample design, sources of bias, and the precision of the estimates. 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; the other sources of information do not confirm the point at which the student has left the country. This lack of ability to verify and triangulate the estimate means that assurances cannot be given to provide the same level of confidence in the former-student emigration figures. OSR noted they 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 reported 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”. OSR therefore asked Office for National Statistics (ONS) 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. This judgement applies only to the student migration component of ONS’s migration statistics; it is not a judgement about the quality of the overall estimates of immigration and emigration derived from the International Passenger Survey (IPS).

As a result, from 24 August 2017 we labelled the former student emigration estimate as Experimental Statistics in all publications. Once we are satisfied that we have a sufficient understanding of former student outcomes, including the extent to which the IPS accurately captures student departures, we can request OSR reassess the former student emigration estimate. Our latest understanding of student migration can be found in "What's happening with international student migration?".

3.15 Is it possible to produce alternative breakdowns of net migration, for example excluding students or asylum seekers?

Office for National Statistics (ONS) may consider alternative breakdowns of any published figures where it would be helpful. Current sources that measure net migration limit the types of alternative variations that can be produced, for example, the International Passenger Survey (IPS) is not suitable for identifying how many students leave the UK in isolation since some non-EU students may remain in the UK after their studies and switch to non-study visas, apply for settlement and others may eventually become British citizens. However, administrative data sources are being developed that may provide a better understanding of student migration in the UK, particularly what students do following their studies. Development plans for improving international migration statistics are outlined in an article published February 2017: International migration data and analysis: Improving the evidence.

If an alternative net migration figure excluding students were produced the impact of doing so would vary depending on whether international student immigration is stable, increasing or decreasing:

  • if stable each year: there will be no impact on net migration of removing students because they will either emigrate after their studies or will remain in the UK, contributing to the non-student population who are resident in the UK and therefore still be included in the net migration excluding students data

  • if increasing each year: excluding students is likely to initially result in a lower net migration figure, depending on the length of their study; if immigration were to stabilise, the size of the initial decrease would reduce each year resulting in little or no impact on the net migration figures in the long-term

  • if decreasing each year: net migration will initially be higher if students were excluded, as previous, if immigration for study were to then stabilise, the size of the initial increase would lessen each year resulting in little or no impact on the net migration figures in the long-term

3.16 How does the UK compare with how other countries measure migration?

It is difficult to accurately compare migration trends internationally, because countries have different ways of defining what is meant by a long-term migrant. Table 2 compares various countries' definitions of long-term migration and how it is measured.

3.17 How do other countries define net migration?

In general, net migration refers to the difference between the number of migrants entering a country and the number leaving it over a given period of time.

Number of immigrants minus number of emigrants equals net migration

Beyond this general definition, different countries may have different criteria for deciding which migrants to include in this calculation and which to leave out.

An important consideration for many countries, including the UK, is the UN-recommended definition of 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". Net migration figures for many countries, including Australia, Canada, Germany, New Zealand and the USA refer to the "usually resident" population of international migrants.

It should be noted that there are different ways of defining "usually resident’". In New Zealand, as in the UK, "usually resident" means being resident for 12 months or more. In Australia, however, it means being resident for at least 12 of the 16 months prior to when the estimate is made. Nevertheless, these countries refer to the ‘"usually resident" population in net migration estimates, regardless of visa status, or whether people are migrating for study, work or other reasons. The main exception to this approach is with regards to foreign military and diplomatic personnel, who are excluded from net migration figures in several countries (including the UK), regardless of the duration of their posting.

Notes for: Methods and coverage

  1. "Economic impact on the London and UK economy of an earned regularisation of irregular migrants to the UK", London School of Economics, (Greater London Authority, 2009)

  2. A more recent report has been published by Migration Watch who have updated the LSE report based on several different assumptions

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4. Reliability of migration estimates

4.1 How reliable are these estimates of international migration?

Estimates of Long-Term International Migration (LTIM) are:

To see how these estimates of LTIM measure against the Code of Practice Dimensions of Quality, please see the Quality and Methodology Information Report for Long-Term International Migration.

The results of a review into the quality of LTIM estimates have been described in Question 2.4. This showed that the quality of international migration estimates improved following the introduction of fundamental changes to the International Passenger Survey (IPS). These changes included:

  • redesigning the sample design at the beginning of 2009 to make the survey more focused on identifying migrants

  • rebalancing the IPS interviewer resource away from Heathrow and towards other routes

  • introducing a new IPS processing system early in 2009 to enable improvements to be made to the IPS weighting methodology

Further information on these changes can be found on the Improving Migration and Population Statistics web pages. Further information about the Quality of the IPS in Relation to Migration Flows is also available.

We continue to keep abreast of available administrative sources and explore whether additional administrative data could be used to improve international migration and population estimates. Please see International migration data and analysis: improving the evidence for more details.

4.2 How accurate are these estimates of long-term international migration?

Surveys gather information from a sample of people from a population. Using the International Passenger Survey (IPS) as an example, the population is passengers travelling through the main entry and exit points from the UK including airports, seaports and the Channel Tunnel. The estimates produced are based on only one of a number of possible samples that could have been drawn at a given point in time. Each of these possible samples would produce an estimated number of migrants. These may be different from the true value that would have been obtained if it were possible to ask everyone passing through about their migration intentions. This is known as sampling variability.

The published estimate is based upon the single sample that was taken and is the best estimate of the true value based on the data collected. However, to account for sampling variability, the estimates we publish include a “95% confidence interval”.

The confidence interval is a measure of the uncertainty around the estimate.

Confidence intervals become larger (meaning there is more uncertainty) for more detailed estimates (such as citizenship by reason for migration). This is because the number of people in the sample who have these specific characteristics (for example, EU8 citizens arriving to study) is smaller than the number of people sampled in higher level categories (such as the total number of EU citizens arriving to study). Where possible, it is better to use the highest level breakdown of data available.

We use the widely accepted 95% confidence interval, meaning that over many sampling repetitions under the same conditions, we would expect the confidence interval to contain the true value 95 times out of 100. Equivalently, we can say that there would be a 1 in 20 chance that the true value would lie outside of the range of the 95% confidence interval. Because of this variation, changes in estimates between survey years or between population subgroups may occur by chance. In other words, the change may simply be due to which passengers were randomly selected for interview.

We are able to measure whether this is likely to be the case using standard statistical tests at the 5% level of “statistical significance”. When we report on statistical significance, we provide an assessment of how likely it is that we would see results as unusual as these. if the true value of the population remained unchanged. The phrase "statistically significant at the 5% level" indicates that, if the true value of the population remained unchanged, a result like this would occur less than 5% of the time.

Confidence intervals are reported in the accompanying datasets. You are advised to be cautious when making inferences from estimates with relatively large confidence intervals. For immigration and emigration estimates where the lower confidence interval is below zero you should assume the estimate is above zero. Estimates from a survey could change from one period to the next simply due to sampling variability. In other words, the change may be due to which individuals were selected to answer the survey and may not represent any real-world change in migration patterns.

For information on the accuracy of these statistics, comparing different data sources, and the difference between provisional and final figures, please see the MSQR - information for users.

4.3 What does it mean if a change is statistically significant?

Changes in the estimates from the International Passenger Survey (IPS) from one period to the next may occur simply by chance. In other words, the change may be due to which individuals were selected to answer the survey and may not represent any real-world change in migration.

We are able to measure whether this is likely to be the case using standard statistical tests. These tests examine the difference between two estimates and calculate a confidence interval of the difference. The usual standard is to carry out these tests at the 5% level of “statistical significance”. When we report on statistical significance, we provide an assessment of how likely it is that we would see results as unusual as these if the true value of the population remained unchanged. The phrase "statistically significant at the 5% level" indicates that, if the true value of the population remained unchanged, a result like this would occur less than 5% of the time.

4.4 How do you determine if a change is statistically significant?

When comparing two estimates, a t-test (see Section 4.5) is performed, which results in the calculation of a 95% confidence interval for the difference between these estimates. If this interval excludes the value zero, then we can conclude that the difference is very likely to be a real difference in migration figures and not a result of sampling variation.

A quick method of identifying if the difference between two estimates is statistically significant is to determine if there is an overlap of their confidence intervals. If they do not overlap, then the differences can be described as statistically significant. However, if they do overlap, then a t-test should be performed to determine statistical significance.

4.5 What is a t-test?

A t-test ascertains if the difference between two estimates is statistically significant, that is, if it were repeated with a different sample, the difference would occur 19 out of 20 times.

This test divides the difference of the estimates by the square root of the sum of the squared standard errors. The resulting t-value needs to be greater than 1.96 to be 95% certain that the estimates are different. It can also be used to create a confidence interval around the difference. It calculates the standard error of the difference directly from using the difference between the two individual standard errors.

All main statistical software packages have the functionality required to perform a t-test. If you need assistance with identifying whether the difference between two international migration estimates is statistically significant then please contact migstatsunit@ons.gsi.gov.uk.

4.6 Is there a test that compares LTIM estimates for significance?

Long-Term International Migration (LTIM) is calculated from International Passenger Survey (IPS) estimates with additional components. These are administrative data held on asylum seekers and health card data on migration to and from Northern Ireland. There is also a mathematical adjustment made for those who change their intentions (switcher adjustments).

These additional components result in data that provide a more complete picture of international migration into and out of the UK. However, these additional data sources are not subject to the uncertainty associated with a sample survey, although it is recognised that they are unlikely to be error free (such as incorrect recording of information).

Since February 2014, confidence intervals around the IPS component of LTIM estimates have been shown alongside LTIM estimates to give users an indication of the accuracy of the estimates. Additionally statistically significant changes are highlighted in the LTIM tables. However, you should note that there is no method of quantifying the possible error associated with the non-survey components of LTIM, which are unlikely to be random.

4.7 Why is there sometimes a big change in net migration but it is "not statistically significant"?

Estimates of long-term international migration are primarily based upon data collected by the International Passenger Survey (IPS). As this is a sample survey not every passenger is interviewed so it is possible that the estimates produced will vary depending upon which passengers are selected to be interviewed. Uncertainty is quantified by publishing a "confidence interval" alongside each of our estimates, for example, if an estimate is 100,000 with a 95% confidence interval of plus or minus 10,000, this indicates that there is 95% probability that the true value lies in the range 90,000 to 110,000. Another way to explain this is that our best estimate is 100,000 but that there is a 1 in 20 chance that the true value is actually less than 90,000 or more than 110,000.

When comparing two estimates you have to take into account the uncertainty surrounding each of the estimates. We therefore apply a statistical test before describing any apparent change as being likely to reflect a real increase or decrease. A change that passes this test is described as being "statistically significant".

The net migration confidence interval (that is, the uncertainty around the estimate due to it being based on a sample survey) is calculated using both the confidence intervals for immigration and emigration. This results in a relatively large confidence interval around the net migration estimate. The confidence interval around the change in net migration from one year to the next will also be relatively large as it will be based on the confidence intervals around the two net migration estimates. Therefore, for a change in net migration to be statistically significant the actual observed change in net migration would also need to be large to account for the relatively large confidence intervals.

4.8 What quality assurance has ONS undertaken on these estimates?

Extensive quality assurance has been carried out on the Long-Term International Migration (LTIM) estimates. The Social Survey Division within Office for National Statistics (ONS) are responsible for carrying out the International Passenger Survey (IPS) and producing the IPS estimates. They have carried out quality assurance on the data collected, focusing particularly on the relationship between migrant contacts, visitor contacts and weighted estimates. This included investigating any anomalies and checking the data provided by the Civil Aviation Authority (CAA), which are used to weight the estimates.

IPS data have been examined in relation to estimates for previous years. The focus of this quality checking has been on any statistically significant increases or decreases and the contributing factors for these changes.

The LTIM estimates are quality assured at every stage of the processing.

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5. Definitions and terms

5.1 Migrants

We use the UN recommended definition of a long-term international migrant:

"A person who moves to a country other than that of his or her usual residence for a period of at least a year (12 months), so that the country of destination effectively becomes his or her new country of usual residence".

This is the definition used to calculate net migration and is also used for the UK usually resident population estimate series. This definition does not necessarily coincide with those used by other organisations.

5.2 Citizenship

Citizenship is defined as the nationality of the passport, which the traveller is carrying.

The British Nationality Act 1981, which came into force on 1 January 1983, replaced citizenship of the UK and Colonies with British citizenship, British Overseas citizenship, and British Dependent Territories citizenship. British Overseas citizens are recorded as New Commonwealth citizens, instead of as British citizens. Persons with British Overseas Territories citizenship are shown under the country that issued their passport.

Following a user consultation new citizenship groupings have been introduced to International Passenger Survey (IPS) tables, which group citizenship differently. A list of which countries are in each of the old and new country groupings is also available. More information on the consultation can be found in Question 5.3.

From May 2017, the Migration Statistics Quarterly Report only includes the new country groupings in its tables. From November 2017, annual tables will only include new country groupings.

5.3 Countries and country groups

A range of different country groupings are used in the migration statistics. The various definitions and groupings are defined in the Glossary and in the notes accompanying the tables. Unless otherwise stated, country groups in tables are presented as they were constituted on 1 May 2004.

In 2014, we ran a user consultation on country groups used in the reporting of international migration statistics. A response to the consultation was published and as a result, new country groupings replaced old country groupings in the Provisional quarterly estimates and were added to the annual final tables alongside the old country groupings. A list of which countries are in each of the old and new country groupings is also available.

5.4 Main reason for migration

Migrants in the International Passenger Survey (IPS) are asked the survey question, “What is the main reason for your visit?”. This question was intended to cover all types of travellers to and from the UK; that is, it was not specifically designed for migrants who constitute only a tiny group of the survey contacts. Nevertheless, it provides our only source for information about reasons for entering or leaving the UK. It should be noted that a person’s main reasons for entering the UK might not be their only reason, for example, someone arriving to study may also work while in the UK. The “main reason for migration” groupings used in the tables are explained in this section:

Definite job

Those migrating who have a definite job to go to, on "business" (excludes diplomats, military personnel, merchant seamen and flight crews) and au pairs; previously known as “work-related”

Looking for work

Those migrating for work reasons, but who do not have a definite job to go to; new category in 2005 which was previously part of the “Other” category

Work-related

Those migrating who either have a definite job to go to or who are looking for work; estimates for these two categories are summed together to produce the estimates for this category

Formal study

Those whose main reason for migrating is to attend a formal study course in the UK; includes unaccompanied school children

Accompany or join

Those migrating to "accompany or join" a partner or immediate family; includes those migrating to get married and those who, on prompting, gave no further reason of their own for migrating

Other

This category includes working holidaymakers, asylum seekers, those visiting friends and family, anyone taking a long holiday as well as migrants who are travelling for religious reasons; in previous published tables, this category also included those "looking for work"

Going home to live

Those migrants who were "going or coming home to live" and would not give any other reason relating to work, study or accompany or join when prompted

No reason stated

Those migrants who were "immigrating or emigrating" and would not give another reason when prompted

Interpreting net migration estimates by reason for migration is not simple. For example, a migrant who arrived in the UK to study may subsequently leave to take up a job abroad, and until January 2012, the IPS did not record the initial reason for coming to the UK when interviewing those migrants leaving. The net migration figures are the difference between the numbers of migrants arriving to study and the numbers of migrants leaving to study, so do not consider the same cohort of people. To avoid potential confusion about the contribution that particular groups of migrants make to total net migration figures, the previously published “balance” figures by reason have been removed.

In 2012, a new question was introduced to the IPS to collect information on an emigrant's main reason for previously immigrating to the UK. This categorised emigrants by whether they had previously immigrated for work, study, accompany or join, or other reasons. The Office for Statistics Regulation (OSR) published a report on 27 July 2017 on The quality of the long-term student migration statistics. Their main focus was the “student migration gap” – the large 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 IPS emigration estimate of former students does not provide 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. Given this, a requirement from the OSR was to label the former student emigration estimate as Experimental Statistics. What’s happening with international student migration? provides the latest update on our work in this area.

5.5 Usual occupation (prior to migration)

The International Passenger Survey (IPS) includes the following question “What has been your regular occupation?” to ascertain usual occupation prior to migration. This question was designed for migrants only. The usual occupation groupings used in the tables in this section:

Professional and managerial:

Administrators, managers, and people with professional and technological qualifications.

Manual and clerical:

All other occupations.

Other adults:

Includes retired people and people with no paid occupation.

Children:

Those aged under 16 years.

Other categories available are:

“Students” and “Total employees” (which is a sum of the “Professional and managerial” and “Manual and clerical” groupings).

Migrants who, prior to migration, were students but undertaking part-time work are grouped as “Professional and managerial” or as “Manual and clerical” (according to the nature of their part-time work) and not as “Students”.

Interpreting net migration estimates by usual occupation is not simple. For example, a migrant whose usual occupation prior to arriving in the UK was a student may subsequently have a different usual occupation when emigrating from the UK.

5.6 Area of destination or origin within the UK

This is shown by countries of the UK (Scotland, Wales and Northern Ireland), and regions of England; North East, North West, Yorkshire and The Humber, East Midlands, West Midlands, East of England, London, South East and South West.

Estimates for Northern Ireland are included in the UK total in the provisional and final International Passenger Survey (IPS) tables and the provisional Long-Term International Migration (LTIM) tables, but are only shown separately in the final LTIM tables from 2008 onwards.

Calibration is used to improve the regional distribution of immigrants. IPS data are adjusted to the geographical distributions provided by the Labour Force Survey (LFS) (known as “calibration”). Further information can be found in the Methodology paper (see Section 3.1.2).

5.7 Age groups

The following survey question is asked of migrants and long-stay visitors in the International Passenger Survey (IPS) "What is your age now?" Results from this question are aggregated and presented as broad age groups: All ages, Under 15, 15 to 24, 25 to 44, 45 to 59 or 64 and 60 or 65 and over. Further explanation of the older age groups is given in this section.

45 to 59 or 64:

This age group includes females aged 45 to 59 years and males aged 45 to 64 years to reflect the differing traditional UK retirement ages between the sexes.

60 or 65 and over:

This age group includes females aged 60 years and over and males aged 65 years and over to further reflect the different ages at which males and females traditionally retire.

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6. A guide to the published tables

6.1 Symbols

The symbols used in the tables are:

: not available
z not applicable
. no contact
0~ rounds to zero
p year includes provisional estimates

6.2 Provisional IPS tables

Provisional International Passenger Survey (IPS) estimates are published in two tables and one chart:

  • Table 3 – International Passenger Survey (IPS) estimates of long-term international migration by citizenship and main reason for migration

  • Table 4 – International Passenger Survey (IPS) estimates of long-term international emigration by citizenship, and for former immigrants, by previous main reason for immigration

  • Chart 3 – All migrants by citizenship and by all main reasons for migration

Table 3 and 4 use 95% confidence intervals to indicate the robustness of each estimate.

Provisional IPS tables and charts can be found within our provisional quarterly estimates.

6.3 Provisional LTIM tables

Provisional Long-Term International Migration (LTIM) estimates are published in two tables and four charts:

  • Table 1 – Provisional estimates of Long-Term International Migration (LTIM) by citizenship

  • Table 2 – Provisional estimates of Long-Term International Migration (LTIM) by main reason for migration

  • Chart 1 TS – Long-term international migrants, citizenship

  • Chart 1 Net – Overall composition of migration by citizenship

  • Chart 2a – Long-term international migrants, immigration/emigration by main reason for migration

  • Chart 2b – Long-term international migrants, main reason for migration

From February 2014, provisional LTIM tables include IPS confidence intervals to indicate the reliability of each estimate.

Provisional LTIM tables and charts can be found within our provisional quarterly estimates.

6.4 Final LTIM and IPS tables (1975 to 2015)

All tables listed in this section can be linked to direct from our Table of Contents.

The estimates given in these tables must be considered alongside the confidence intervals that are given for each estimate. When subtracted from and added to the estimate this gives the range within which the true value of the estimate is expected to be (with 95% confidence). The confidence intervals for the International Passenger Survey (IPS) estimates are relatively large where the estimates are based on a small number of contacts. A larger confidence interval indicates greater uncertainty over the true value of the estimate. For immigration and emigration estimates where the lower confidence interval is below zero you should assume the estimate is above zero.

More information on confidence intervals is given in the published Table 1.02 and in the Migration Statistics Quarterly Report Information for Users.

The tables are grouped into series:

  • 1-series, Tables 1.01 to 1.03; these tables relate to aspects of the methodology

    • Table 1.01, Long-Term International Migration (LTIM) components and adjustments, 1991 to 2015; this table shows the components and adjustments that make up the estimates of LTIM for the UK, from 1991 to the latest year and should be viewed in conjunction with the Methodology paper, which covers the methodology used to produce LTIM (see Section 3.1.2)
    • Table 1.02, IPS margins of error, 1975 to 2015; this table provides contact figures and confidence intervals for individual variables provided in the 3-series tables
    • Table 1.03, IPS non-response, 1977 to 2015; this shows the percentage of migrants who did not give a response to specified IPS migration questions and whose response was therefore imputed
  • 2-series, Tables 2.01 to 2.11, LTIM tables, 1991 to 2015; these tables show a time series of estimates of Long-Term International Migration (LTIM) for the UK, and for England and Wales, they are by calendar year unless otherwise stated.

    • 2.01a, LTIM citizenship, 1991 to 2015
    • 2.01b, LTIM citizenship, half-years, 2002 half-year 1 to 2015 half-year 2
    • 2.02, LTIM country of last or next residence, 1991 to 2015
    • 2.03, LTIM country of birth, 1991 to 2015
    • 2.04, LTIM main reason for migration, 1991 to 2015
    • 2.05, LTIM usual occupation prior to migration, 1991 to 2015
    • 2.06, LTIM area of destination or origin within the UK, 1991 to 2015
    • 2.07, LTIM age and sex, 1991 to 2015
    • 2.08, LTIM sex and marital status, 1991 to 2015
    • 2.09, LTIM intended length of stay, 1991 to 2015
    • 2.10, LTIM citizenship, mid-years between 1991 to 1992 and 2014 to 2015
    • 2.11, LTIM area of destination or origin within the UK, mid-years between 1991 to 1992 and 2012 to 2013 (please note this table has been discontinued, a link to more accurate regional migration data can be found within the published 2013 table)
  • 3-series, Tables 3.01, IPS tables, 1975 to 2015; these tables show estimates of long-term international migration based on IPS only, they are more detailed, showing a cross-tabulation of at least two variables and cover each calendar year, from 1975 unless otherwise stated.

    • 3.01, IPS citizenship by country of last or next residence, 1975 to 2015
    • 3.02, IPS country of last or next residence by area of destination or origin within the UK, 1975 to 2015
    • 3.03a, IPS country of last or next residence by sex, 1975 to 2015
    • 3.03b, IPS country of last or next residence by age, 1975 to 2015
    • 3.04, IPS country of birth by sex, 1975 to 2015
    • 3.05a, IPS citizenship by sex, 1975 to 2015
    • 3.05b, IPS citizenship by age, 1975 to 2015
    • 3.06, IPS area of destination or origin within the UK by age, 1975 to 2015
    • 3.07, IPS area of destination or origin within the UK by sex, 1975 to 2015
    • 3.08, IPS citizenship by main reason for migration, 1977 to 2015
    • 3.09, IPS country of last or next residence by main reason for migration, 1977 to 2015
    • 3.10, IPS usual occupation prior to migration by main reason for migration, 1977 to 2015
    • 3.11a, IPS main reason for migration by sex, 1977 to 2015
    • 3.11b, IPS main reason for migration by age, 1977 to 2015
    • 3.12a, IPS usual occupation (prior to migration) by sex, 1976 to 2015
    • 3.12b, IPS usual occupation (prior to migration) by age, 1976 to 2015
    • 3.13, IPS citizenship by usual occupation (prior to migration) and sex, 1976 to 2015
    • 3.14, IPS citizenship by area of destination or origin within the UK, 1975 to 2015
    • 3.15, IPS actual length of stay by citizenship, 1977 to 2015
    • 3.16, IPS actual length of stay by country of last or next residence, 1977 to 2015
    • 3.17, IPS intended length of stay by country of last or next residence, 1985 to 2015
    • 3.18, IPS country of birth by country of last or next residence, 1975 to 2015
    • 3.19, IPS citizenship by route (combined 2 year groupings), 1977 to 2015
    • 3.20a, IPS top 15 countries of last or next residence of all migrants, 1975 to 2015
    • 3.20b, IPS top 10 countries of last or next residence of migrants who are British citizens, 1975 to 2015
    • 3.20c, IPS top 10 countries of last or next residence of migrants who are non-British citizens, 1975 to 2015
    • 3.21, IPS previous main reason for immigration by main reason for emigration, 2015
    • 3.22, IPS previous main reason for immigration by usual occupation prior to emigration, 2015
    • 3.23, IPS previous main reason for immigration by year of arrival in UK, 2015
    • 3.24, IPS citizenship - current and new country groupings, 1975 to 2015
    • 3.25, IPS country of birth - current and new country groupings, 1975 to 2015
    • 3.26, IPS country of last or next residence – current and new country groupings, 1975 to 2015

Please note: From November 2012, all 3-series IPS tables use 95% confidence intervals to indicate the accuracy of each estimate, as opposed to standard error used in previous tables.

  • 4-series, Tables 4.01 to 4.08, IPS tables, 2000 to 2015; these are the underlying datasets of the 3-series, which provide annual estimates of long-term international migration based on IPS only; unlike the 3-series the data are by individual country rather than country grouping.

    • 4.01, IPS citizenship group by sex by age by country of last or next residence
    • 4.02, IPS main reason for migration by citizenship
    • 4.03, IPS country of birth by country of last or next residence
    • 4.04, IPS area of destination or origin within the UK by citizenship
    • 4.05, IPS main reason for migration by country of last or next residence
    • 4.06, IPS country of birth by citizenship
    • 4.07, IPS sex by age by citizenship
    • 4.08, IPS sex by age by country of birth
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7. Further information and data requests

7.1 What other information is available on international migration?

The Migration Statistics Quarterly Report (MSQR) series summarises the regular quarterly and annual migration and related data published by the Home Office, the Department for Work and Pensions (DWP) and Office for National Statistics (ONS). The quarterly reports provide main messages from the latest data. Web links are provided at the back of the reports for those who wish to access the underlying datasets.

The Home Office publish quarterly statistics that relate to people who are subject to immigration control under Immigration Acts (that is, to people who do not have the right of abode in the UK). They are produced mainly as a by-product of the process of immigration control. DWP provide quarterly figures for the number of National Insurance numbers (NINo) allocated to overseas nationals, for the purposes of work, benefits or tax credits, entering the UK.

More information on these statistics can be found in the Migration Statistics Quarterly Report.

Other migration data released on an annual basis include the international migration component of the mid-year population estimates and “Migrant 4 GP Registrations” and can be compared at the local level using the Local Area Migration Indicators Tool.

7.2 Can I request further information on migration?

It is possible to request more detailed information and data on international migration by emailing the Migration Statistics Team at migstatsunit@ons.gsi.gov.uk.

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8. Glossary

This glossary includes words found in documentation related to the long-term international migration estimates, which are not explained previously.

Calibration

An estimation procedure that constrains sample-based estimates of auxiliary variables to known totals (or accurate estimates). Calibration is used to improve the regional distribution of immigrants. Further information can be found in the Methodology paper (see Section 3.1.2).

Coherent reporting

Key information on migration which has been collected across government. The report provides a united approach to the release of statistics on migration, helping customers and the public to understand the different outputs published.

Confidence interval

This is the range within which the true value of a population parameter lies 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 to find the true value 95 times out of 100. Equivalently, we can say that there would be a 1 in 20 chance that the true value would lie outside of the range of the 95% confidence interval. The uppermost and lowermost values of the confidence interval are termed “confidence limits”.

Country of usual residence

Based on the UN definition, the country in which a person has a place to live, where he or she normally spends the daily period of rest. Temporary travel abroad for purposes of recreation, holiday, visits to friends and relatives, business, medical treatment or religious pilgrimages does not change a person’s country of usual residence.

EEA

The European Economic Area (EEA) consists of the 28 countries of the EU (see next definition), plus Iceland, Liechtenstein and Norway. Swiss nationals are treated as EEA nationals for immigration purposes; however for statistical purposes Switzerland is not included in EEA estimates by ONS.

European Union

Between 2007 and 2013, EU2 nationals had certain restrictions placed on them; in the first 12 months of stay, working Bulgarian and Romanian nationals were generally required to hold an accession worker card or apply for one of two lower-skilled quota schemes. Other Bulgarian and Romanian nationals could apply for a registration certificate, giving proof of a right to live in the UK. These restrictions were lifted on 1 January 2014. EU8 nationals previously had restrictions on their rights to work and were required to register under the worker registration scheme, but these restrictions were lifted from 1 May 2011.

Emigrant (outflow)

A person who leaves their country of usual residence to take up residence in another country for a period of at least 12 months.

Estimate

An indication of the value of an unknown quantity based on observed data. The estimated number of migrants is calculated by weighting up the number of contacts collected by the IPS. Further information about the weightings used by the IPS can be obtained in this overview of International Passenger Survey (IPS).

Immigrant (inflow)

A person arriving or returning from abroad to take up residence in a country for a period of at least 12 months.

IPS

The International Passenger Survey (IPS) is a survey of a random sample of passengers entering and leaving the UK by air, sea or the Channel Tunnel. Between 700,000 and 800,000 people are interviewed on the IPS each year. Of those interviewed, approximately 4,000 people each year are identified as long-term international migrants.

LFS

Labour Force Survey – a quarterly household survey run by ONS.

Long-term international migrant

ONS uses the UN recommended definition of a long-term international migrant: “A person who moves to a country other than that of his or her usual residence for a period of at least a year (12 months), so that the country of destination effectively becomes his or her new country of usual residence.”

This is the definition used to calculate net migration, and is also used for the UK usually resident population estimate series. This definition does not necessarily coincide with those used by other organisations.

LTIM

Long-Term International Migration (LTIM) estimates are produced by combining migration data from the International Passenger Survey (IPS), Home Office data on asylum seekers (including non-asylum enforced removals adjustment and people resettled in the UK under various resettlement schemes), migration to and from Northern Ireland (from the Northern Ireland Statistics and Research Agency) and adjustments for visitor switchers and migrant switchers.

Margins of error

The margins of error express the maximum expected difference (positively and negatively) between the true population and a sample estimate of that population. The margin of error is qualified by a probability statement, which is expressed in the form of a confidence interval (see definition).

Migrant switchers

Travellers who stated the intention in the International Passenger Survey (IPS) to stay in the destination country for at least a year, who were therefore counted as migrants, but who actually left sooner.

Migration Statistics Improvement Programme (MSIP)

The Migration Statistics Improvement Programme (MSIP) at ONS worked to improve the quality of population and migration statistics, which aimed to make migration statistics as accurate as possible and relevant for user needs. Further information is available on the MSIP webpage.

Net emigration (outflow)

A situation where more people are migrating out of a country (for at least 12 months) than are entering that country in a given time period.

Net immigration (inflow)

A situation where more people are migrating into a country (for at least 12 months) than are leaving that country in a given time period.

Net migration (flow or balance)

The difference between immigration and emigration.

New Commonwealth

The new Commonwealth statistical grouping consists of African Commonwealth countries (Botswana, Cameroon, The Gambia, Ghana, Kenya, Lesotho, Malawi, Mauritius, Mozambique, Namibia, Nigeria, Seychelles, Sierra Leone, Swaziland, Tanzania, Uganda, Zambia and Zimbabwe), Indian subcontinent countries (Bangladesh, India, Pakistan and Sri Lanka), and other Commonwealth countries in the Asian, Caribbean, and Oceanian regions.

It also includes British Overseas Territories. Up to and including 2003, Malta and Cyprus are included in the new Commonwealth grouping. From 2004, the year of accession, they are included in the EU. Malta and Cyprus are members of both the Commonwealth and the EU from May 2004 onwards. However, for estimation purposes they have only been included in the EU grouping for 2004 onwards.

Rwanda was admitted to the Commonwealth in November 2009, but the definition for this statistical grouping has remained unchanged. Zimbabwe and The Gambia withdrew from the Commonwealth in 2003 and 2013 respectively, but again the definition for this grouping has remained unchanged.

New country groupings

We introduced new country groupings in 2014. These are available for both IPS and LTIM estimates. A listing of which countries are in each of the old and new groups is available.

From May 2017, old groupings are not available in the provisional tables and from November 2017 they are not available in the annual tables.

Non-contacts

People counted by the International Passenger Survey (IPS) but not interviewed. For example, during peak periods an interviewer may not finish an interview before their next assigned contact has crossed the IPS counting line.

Non-response

Failure to obtain any survey information due to respondent refusal, non-contact or inability to reply.

Non-sampling error

Non-sampling errors may arise from many different sources. These may include misunderstanding or misreporting by respondents, variations between the way interviewers administer the survey, non-coverage of the population due to an inadequate sampling frame or sample design and errors made when processing the error attributable to all other sources other than sampling.

Old Commonwealth

The Old Commonwealth statistical grouping consists of four countries: Australia, Canada, New Zealand and South Africa.

Other Foreign

Other Foreign is defined as the non-EU countries within Europe, the United States of America, the Middle East, and the remaining countries in North, Central and South America, Africa, Asia and Oceania which are not included in either the New or Old Commonwealth country groupings.

Rolling year

Any 4 consecutive quarters that make up a 12 month period. In the provisional tables the rolling year moves on 1 quarter for each row of estimates in the tables. For example the rolling year January 2009 – December 2009, is followed by the rolling year April 2009 to March 2010.

Sampling error

The difference between an estimate derived from a random sample and the true population value; the difference being attributable to the fact that only a sample of values was used. That is, sampling error results because not every migrant who enters or leaves the UK is interviewed.

Standard error (SE)

An indication of the accuracy of an estimate and how much a sample estimate is likely to differ from the true value because of random effects.

Visitor switchers

Visitors who enter or leave the UK intending to stay in the destination country for less than a year but who actually stay for a year or longer.

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