International migration research, progress update: November 2024

This article provides an update on research to further develop admin-based migration estimates (ABMEs). For detailed information on our current methods and quality, please refer to our Provisional Long-Term International Migration: Technical User Guide.

We are continuing to develop timely and coherent migration and population estimates at both national and local authority level, as part of the development of an admin-based population estimate (ABPE). For the most recent ABPE publication, please see our Dynamic population model, improvements to data sources and methodology: local authorities in England and Wales, mid-2011 to mid-2023 article.

We continue to use the Home Office Borders and Immigration (HOBI) data to estimate long-term migration of non-EU+ nationals. For November 2024, we have widened our EU category to EU+. This includes all EU countries and Iceland, Liechtenstein, Norway, and Switzerland. In our May 2024 International migration research update, we set out plans to improve the methods used to estimate long-term immigration and emigration. This included:  

• accounting for people who transition onto a new visa at the end of their initial visa, but had not travelled on their new visa 

• improving the early leavers adjustment to take into account characteristics such as nationality and age  

These improvements, along with some others, have been implemented in our Long-term International Migration bulletin, published in November 2024. 

Visa transitions 

In our International migration research, progress update: November 2023 article, it was acknowledged that when an international migrant comes to the end of their visa and transitions to a new visa and does not travel on it before the end of the period covered by the data extract, they were classed as a long-term emigrant despite the fact some will have remained in the UK and not yet emigrated. This is because when an individual was missing their last departure and also had no open visas linked to their travel data, we were assuming that there was a missed last departure and classified them as having emigrated.  

If they then travelled on this new visa, we would subsequently be able to identify them as remaining in the country and remove them from the emigration estimates, leading to revisions to our previous emigration estimates. 

Missed departures can occur from travel through the Common Travel Area or from instances of travel not successfully linked to a visa. However, some of these people will have acquired a new visa while in the country and have yet to travel on it, so they remain in the UK legally and therefore should not be classified as having emigrated. 

In our November 2023 and May 2024 published estimates of non-EU+ international migration, we applied an adjustment to account for this over-estimation of emigration and to limit the scale of potential revisions to emigration estimates. This was an aggregate level adjustment, which took the percentage difference in emigration between the provisional and updated data from the previous two data extracts and applied this to the most recent reference period by reason for migration. 

However, now we have improved our method, we can see that, particularly for those arriving on family, study-dependent and work-dependent routes, this adjustment did not go far enough in reducing emigration estimates. The reason this adjustment failed to fully adjust for these populations was that the adjustment was unable to account for people who either never travelled on their new visa, or who took more than six months to travel on their new visa. This meant these individuals were still being incorrectly classified as long-term emigrants in the updated data extract used in the percentage difference calculation. 

For the first time, we have been able to link data on someone's travel history to visas that have not yet been travelled on. This has allowed us to implement a method change to identify these new visas, acquired in country but not travelled on, at an individual migrant level. This means our estimates no longer require an emigration visa transitions adjustment. This linkage provides us with a more accurate understanding of whether they remain in the country or not and should minimise the scale of future revisions because we no longer need to wait for them to travel on their new visa to be identified as still in the country. 

Missing first arrivals 

To estimate migration using the First Arrival Last Departure method, explained in our Provisional long-term international migration estimates: technical user, we impute missing first arrival dates for people with future travel records from the UK using visa start date as a proxy. We analysed the people who had a missing first arrival who were classified as long-term immigrants based on subsequent travel data and in year ending June 2024, this was 11,000 people. Our analysis found that of those, 22.7% travelled on in-country 10-year family or private life visas, and 55.2% were young children on child visas, likely born in the UK.  

We do not have sufficient travel data from earlier years to determine when or if these individuals arrived in the country, but our analysis suggests they did not arrive in the reference year and have been in the UK for a long time. As a result, we have updated our method to exclude individuals with a missing first arrival travelling on these visas from the immigration estimates. This has revised immigration estimates down but these individuals remain in the data, so emigration estimates are unaffected if they leave in the future. The remaining 22.1% of people who are not in these two groups remain in the long-term emigration estimates.  

Long-term travel outside the UK within a visa period 

Our previous methodology did not account for individuals who spent large amounts of time outside the UK during their visa period, we have now improved the method to better account for this. Over the pandemic, we saw more people leave long-term -- for 12 months or more -- during their visa period and arrive in the UK towards the end of their visa. We have done further work on this group to align with the United Nations definition (PDF, 5.0MB) and now count individuals who have left the UK for more than 365 days during their visa period as an emigrant. A new visa period is then started when the individual next arrives in the UK, some of these individuals will go on to be long-term immigrants if they meet the UN definition.  

Visit visas 

A Visit visa allows an individual to stay in the UK for a maximum of six months. Therefore, all instances of Visit visas are excluded from the estimates as it does not permit an individual to be within the UK for 12 months or more. 

Previously, time spent in the UK as a visitor could count towards an individual's total length of stay in the UK if they were not on a long-term visit visa. This meant that someone visiting the UK could be counted as an immigrant at the point of their initial visit, despite not being a long-term migrant at that point. We now only count someone's length of stay from the point at which they transition onto a long-term visa.

We use the UN definition of a long-term international migrant, which is 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. Waiting 12 months for travel data to confirm people's long-term migration status conflicts with user needs for more timely statistics. To resolve this, we make assumptions about people's expected length of stay or departure based on past trends, to produce an adjustment that provides a provisional estimate for more recent periods. Provisional estimates have a greater level of uncertainty as trends can change; this uncertainty decreases as time passes and more data are incorporated.

In our May 2024 Long-term international migration, provisional bulletin, we identified that changing the way we produce provisional estimates of long-term immigration by improving the early leavers adjustment would improve the accuracy of these estimates. This research identified that accounting for differences in nationality and age, as well as visa type in our assumptions, is more representative of the migrants to whom the adjustment is applied.

Immigration early leaver adjustment

An early leaver is defined as an individual who arrives on a long-term visa but does not stay for at least 12 months and therefore does not become a long-term migrant. For those who arrived in the last 12 months, we use past behaviour to estimate how many will leave before that point and remove them from our aggregated final estimates. In the current release, the adjustment covers those who arrived or departed between July 2023 and June 2024.

We have improved the early leavers adjustment by including more characteristics. It is now applied by reason for migration, nationality, and age group to reflect the distinctive behaviour patterns seen in different groups.

In May 2024, we based our assumptions on data for YE December 2020, 2021, and 2022, with 2022 double weighted to more strongly represent recent trends. However, based on the research on our provisional estimates of long-term immigration published in May 2024, we now base the assumptions on the most recent time period available, for this release it is YE June 2023.

Here are a couple of examples showing why the new assumptions are better.

Figure 1 shows the early leaver proportions for those aged 18-29 years on long-term study visas and the assumption used for YE June 2024 based on YE June 2023 proportions. Our previous May 2024 publication assumed that 16% of arrivals on long-term study visas did not become long-term migrants, but the new method breaks this down by age and nationality and shows notably different proportions at this level. Using age and nationality allows the high variance in early leavers on study visas to be better reflected in our adjustment.

Figure 2 includes early leaver proportions for those aged 30 to 44 years on long-term work visas. The early leavers assumption in May 2024 assumed that 5% of arrivals on long-term work visas did not become long-term migrants. The new method shows lower proportions among the top nationalities, though these remain more consistent compared with study visas.

We have revised estimates for year ending (YE) June 2021 to YE December 2023 that were published in May 2024. Further details on revisions can be found in our Revisions Policy. The size and reasons for the revisions are shown in the following tables 1 and 2.

Non-EU immigration

The revision to the immigration of non-EU+ nationals in YE December 2023 is driven by four main factors.

Visa transitions

The biggest factor is the introduction of the visa transitions method improvement, as described in Section 2: Improvements to the method for estimating non-EU+ migration. This improved method has led to an increase in our immigration estimates, as it allows us to identify individuals who initially only had a short-term stay but extended this onto a long-term visa while in the country to now meet the definition of a long-term migrant. Previously, we would not have identified this transition to a new visa until they travelled on it. Inclusion of this visa in our data at the time it is obtained should further decrease the scale of revisions to our estimates in future publications. In YE December 2023, this has increased the immigration estimate by 34,000.  

Updated and complete Information

The Home Office Borders and Immigration (HOBI) data are part of a live database that is continuously updated with new information on travel and visas granted. These updated data lead to revisions to our immigration estimates for a variety of reasons, including:

• individuals who originally arrive on short-term visas are not initially included in our immigration estimates; some of these individuals are granted another visa that extends their stays in the UK to over 12 months, and should be counted as long-term immigrants

• individuals who are on visas of less than a year may overstay their visas and therefore extend their stays in the UK to over 12 months, and should be counted as a long-term immigrant

When we published our estimates in May 2024, we did not have complete data to say whether those who arrived, for example in September 2023, would stay long-term for YE December 2023 period. For those who arrived between January and June 2023, we now have 12 months of travel data to say whether they subsequently stayed long-term. However, for those who arrived between July and December 2023, we still rely on an adjustment to estimate how many will stay long-term. We have also updated the assumptions for those arriving between July and December 2023 (see Section 2: Improvements to the method for estimating non-EU+ migration). These updated data have revised our immigration estimates for YE December 2023 up by 50,000.

Our ongoing research has led to a better understanding of people on the Ukraine Schemes and other visa types. We now know we were missing some people arriving on these visa types. We have corrected this, and this has increased our immigration estimate by 17,000 in YE December 2023.

Method improvements

We have made a number of small improvements to our method. For YE December 2023, removing some people with a missing first arrival revised immigration estimates down by 13,000. For the same time period, removing arrivals on visit visas revised immigration estimates down by 1,000, and accounting for long-term travel outside the UK within a visa, revised immigration estimates up by 4,000.

Asylum and resettlement

Finally, in addition to the revisions for visa data, we have also updated data for those applying for asylum and resettlement. As we gather more complete data and the Home Office live system updates, our estimates are revised. We have revised our immigration estimates for YE December 2023 down by 1,000 for this reason.

Non-EU emigration

For YE December 2023, we have revised our emigration estimates down by 69,000, there are three main reasons for this.

Visa transitions

The change resulting in the largest revision is the visa transitions method improvement. More information on this improvement is available in Section 2: Improvements to the method for estimating non-EU+ migration. This has decreased emigration in YE December 2023 by 110,000 where we can now see individuals who have moved onto a new long-term visa at the end of their initial visa.

Updated information

We now have complete travel information to show whether people who left between January and June 2023 moved onto another visa or remained out of the UK for 12 months and updated data up until June 2024. For YE December 2023, this has increased emigration by 26,000. Our ongoing research has led to a better understanding of people on the Ukraine Schemes and some other visa types. We now know we were missing some people arriving and departing on these visa types and this has increased our emigration estimate by 23,000 for YE December 2023.

Method improvements

We have also made some further small method improvements. By removing visit visas and accounting for long-term travel outside the UK, our emigration estimates for YE December 2023 have decreased by 8,000.

Revisions made to the EU category

For the November 2024 publication, we have widened our EU category to EU+. This includes all EU countries and Iceland, Liechtenstein, Norway, and Switzerland. These nationalities were not included in publications prior to November 2024. As a result, immigration and emigration estimates of EU nationals have been revised from YE June 2021 onwards. Table 3 shows that, as expected, the immigration estimates have been revised upwards as more countries are now included in those estimates. More recent data from RAPID also provides updated data for adjustments made for our recent arrivals and departures.

EU immigration

Table 4 shows the differences between our EU+ immigration estimates, and what the immigration estimates would have been if our original EU grouping had been used. The YE March time period reflects that RAPID is a financial year dataset ending March each year.

EU emigration

Tables 5 and 6 show how the inclusion of Iceland, Liechtenstein, Norway and Switzerland, plus an updated data supply from RAPID has also affected EU+ emigration. Updated RAPID has a big impact on emigration because March 2022 estimates in RAPID 8 now include self-employed data, whereas the previous estimates were based on data that had a rolled-over self-employment component. The YE March 2023 estimate previously published is a forecast, whereas this March 2023 estimate is based on activity data.

Table 6 shows the differences between our EU+ emigration estimates, and what the emigration estimates would have been if our original EU grouping had been used. The YE March time period reflects that RAPID is a financial year dataset ending March each year.

Long-term international migration (LTIM) estimates are published with accompanying uncertainty intervals for net migration, immigration, and emigration. We construct the uncertainty intervals using simulated studies, with a wider interval indicating more uncertainty with the estimate. The uncertainty intervals in this bulletin do not account for all sources of potential uncertainty estimates of long-term international migration. Our working series paper, Quantifying uncertainty in headline international migration estimates, outlines the current quantified and unquantified sources of uncertainty.  

In our latest bulletin, [published in November 2024], we have made one refinement in our approach for quantifying uncertainty with the early leavers' adjustment for non-EU+. Our method requires estimating both a mean and standard deviation as parameters for a normal distribution. We then draw (simulate) 10,000 plausible values of early leavers proportions from this normal distribution. 

Previously, for estimating the mean and standard deviation, we used three or four years of historical data. Reviewing our approach has indicated that it is not optimal for capturing recent trends and behavioural changes with percentages of early leavers. We now use the two most recent years to estimate the mean and retain using four years to estimate the standard deviation. This helps to achieve a more optimal balance between recent trends and historical variability.

EU migration methods

In our International migration research, progress update: November 2023, we updated users on our ambition to move to using the Home Office Borders and Immigration (HOBI) data to estimate the migration of EU nationals as well as non-EU+ nationals. In this update we provided some provisional research into using the HOBI data for EU visa holders, replicating the methods already developed for non-EU+ nationals. We intend to use this in May 2025, after consultation with our users and subject to meeting final quality standards.

We have progressed our research to develop methods to estimate the long-term migration of those with EU Settled Status. This is based primarily on travel data where we have compared two methods.

• cumulative time spent in the UK – this method is designed to be flexible in terms of how long an individual must spend in or out of the UK to be considered a long-term migrant

• 12 months in 16 – this replicates a similar method used by Stats New Zealand and The Australian Bureau of Statistics where someone must spend 12 months in any 16-month period in or out of the UK to be considered a long-term migrant

We will provide users with a further update on this research in 2025.

British nationals methods

Registration and population interactions database

In future we will no longer able to use the International Passenger Survey (IPS) to measure the immigration and emigration of British nationals because it has transitioned to a tourism-only survey. We currently use the Registration and Population Interactions Database (RAPID) for successfully measuring EU nationals. There are additional challenges to measuring British nationals' migration. RAPID contains every British national with a National Insurance Number (NINo) and their interactions with the tax and benefits system since 2008. The challenge is that non-interaction may not be because of emigration. Similarly, a sudden re-interaction after years of non-interaction may not be because of re-arrival or return to the UK.

Our methodology involves applying flags to a person's record to indicate residency status. The overarching assumption is that people are resident until there are reasonable grounds to assume otherwise. The flag rules, adapted from DWP and developed by the Office for National Statistics (ONS), include rules for single tax year absence, pension, address change, child benefit grace periods, child's parent residency, students, and penultimate year rules.

Each NINo is assumed to represent a unique individual, making RAPID a potential population stock dataset. This dataset can infer migration flows into and out of the UK by observing the start or end of activities. If interactions stop for a sustained period, it may indicate emigration. Unlike the IPS, RAPID is based on recorded activity rather than intentions.

However, there are several quality considerations for the RAPID database. The data, supplied by HMRC and DWP, were originally collected for business needs, not for population and migration purposes. This introduces limitations for the ONS's use. For instance, certain groups, such as migrant children, may not be fully captured unless they apply for a NINo, leading to under-coverage of under-16s. Additionally, there is often a lag in the data because people's activities do not necessarily require people to have a NINo, which can delay the appearance of migrants in the dataset. The methodology used to estimate activity and interactions involves assumptions that might introduce errors.

To address these issues, several data quality initiatives have been implemented. Cross-government data sharing efforts aim to enhance the accuracy and timeliness of data captured in RAPID. Methodological adjustments are continuously developed to better estimate international migration and address coverage gaps. The RAPID system also uses multiple categories to account for the complexity of individuals' lives and interactions, helping to distinguish between long-term and short-term migrants.

Future research areas include adjusting for dual nationalities, accounting for prisoners, reducing under-coverage, improving self-employment data, and analysing the impact of the pandemic tax year. For instance, RAPID does not currently adjust for dual nationalities, and there is an assumption that dual nationals would use their British documents upon arrival. Additionally, prisoners are typically economically inactive and may be flagged as emigrated. For this reason, we use a method to include prisoners, with a sentence of over one year, in the resident stock.

In conclusion, while RAPID has certain issues in measuring UK nationals' immigration and emigration, it offers advantages over the IPS in terms of coverage and accuracy. RAPID captures real interactions with the tax and benefits systems, providing a potentially more accurate reflection of migration behaviours. It includes data from multiple sources, offering a detailed view of individual activities over time, and allows for methodological flexibility through various rules and flags. Our intention is to move to this method in May 2025 for the publication addressing the YE December 2024.

Mirror statistics

This area of research will support the RAPID work by providing a valuable comparator estimate. Mirror statistics involve comparing migration data reported by both the sending and receiving countries to identify discrepancies and improve accuracy. This method is particularly useful for cross-referencing and validating migration estimates. By analysing the differences between the datasets, researchers can gain insights into the reasons behind any inconsistencies. When used in conjunction with the RAPID data, mirror statistics can enhance the estimation of British national migration by providing a more comprehensive view of migration flows. This combined approach allows for a more accurate assessment of migration patterns, as it leverages both the recorded activities in the RAPID database and the bilateral comparisons from mirror statistics.

Advanced Passenger Information (API) dataset

In addition to the RAPID data and the mirror statistics data we plan to explore the Home Office's API data.

A more detailed glossary can be found in our Long-term international migration, provisional: year ending June 2024 bulletin.

Administrative data

Collections of data maintained for administrative reasons, for example, registrations, transactions, or record keeping. They are used for operational purposes and their statistical use is secondary. These sources are typically managed by other government bodies.

Advance passenger information

Advance passenger information (API) comprises records of information provided by passengers to their airline or travel company before travel. The information normally details passport number, the name on the passport, gender, and date of birth.

British national

A British national is a person who holds a type of British (English, Scottish, Welsh, and Northern Irish) nationality. The six different types of British nationality are:

• British citizenship

• British Overseas Territories citizen

• British overseas citizen

• British subject

• British National (Overseas)

• British protected person

For the purposes of our estimates, we have treated British National (Overseas) (BN(O)) as a separate category within the non-EU+ country grouping.

EU and EU+

EU is the European Union. It is the sum of EU14, EU8, and EU2, plus Malta, Cyprus and Croatia (from 1 July 2013). British nationals are not included in these numbers at any point in time.

• EU2 is Romania and Bulgaria.

• EU8 is Czechia, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia.

• EU14 is Austria, Belgium, Denmark, Finland, France, Germany, Greece, Republic of Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain and Sweden.

• Other EU is Malta, Cyprus and Croatia (joined from 2013).

• EU+ is all current EU countries plus Norway, Iceland, Liechtenstein and Switzerland.

Home Office Borders and Immigration data

Combines data from different administrative sources to link an individual's travel in or out of the UK with their immigration history. This system has data for all non-European Economic Area (non-EEA) visa holders.

International Passenger Survey

Our International Passenger Survey (IPS) collects information about passengers entering and leaving the UK and has been running continuously since 1961, except between March 2020 and January 2021 when it was suspended because of the coronavirus (COVID-19) pandemic. Currently, we use it for our British national estimates and for providing information on reason for migration. This is the final release in which IPS will be used in this way. In future, the IPS will be mainly used to measure tourism.

Long-term international migration

Long-term international migration (LTIM) statistics estimate the flow (or movement) of migrants to and from the UK. This publication uses the UN-recommended definition of a long-term international migrant, as explained in the Recommendations on Statistics of International Migration paper (PDF, 5MB). A long-term international migrant is defined as "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."

A long-term international immigrant in this publication refers to a person who has moved to the UK from abroad for a period of at least a year.

A long-term international emigrant in this publication refers to a person who has left the UK to go to another country for a period of at least a year.

Non-EU+

Non-EU+ is the sum of the rest of the world, including the rest of Europe, not included in the EU+ category. British nationals are excluded from these numbers.

Registration and Population Interaction Database

The Registration and Population Interaction Database (RAPID) is a database created by the Department for Work and Pensions. It provides a single coherent view of interactions across the breadth of benefits and earnings datasets for anyone with a National Insurance number (NINo).