Migration statistics

Written evidence submitted by UK Statistics Authority (5STATS 12)

Thank you for your invitation to submit evidence to the Committee’s inquiry into migration statistics .

The UK Statistics Authority has conducted a range of work on migration statistics. As you noted in your call for evidence, the Authority published Migration Statistics: The Way Ahead in July 2009. [1] The Authority also conducted a monitoring review [2] of official immigration statistics in 2011. We have concluded that while Parliament, Government and the public all demand a comprehensive, highly accurate statistical picture of immigration and emigration, this is not, in practice deliverable without the systematic recording of people and detailed information about their intentions (such as when they will leave and why they are migrating) when entering and leaving the UK. Such systematic recording is not something that statistical offices can establish for themselves. It would require Parliament and Government to put the necessary framework of legislation and administration in place. Nonetheless, since 2008, the Office for National Statistics (ONS) has led a cross-departmental programme of work on migration statistics which has resulted in some significant improvements within those constraints.

The Committee asked six questions about international migration statistics. Some general observations from the UK Statistics Authority’s perspective are set out below. Detailed operational information, from the perspective of producers of migration statistics, is provided in the attached Annex.

1. Meeting user needs

ONS has on-going engagement with a range of users of migration statistics (see Annex). While the Statistics Authority believes that this question is mainly for the users of migration statistics to answer, our discussions lead us to believe that the currently published figures on migration are unlikely to be regarded as fully satisfactory. There appear to be two particularly demanding uses of these statistics – local authorities’ use in planning the provision of services (which requires robust statistics at the local level), and the needs of Parliament, Government and the public in monitoring progress against the Government’s objective of reducing net migration. The latter also requires quite precise and consistent estimates of net migration, computed from the difference between immigration and emigration. These two demanding sets of user requirements mean that alternative proxy measures are unlikely to meet the needs of all users. Our understanding is that the currently available statistics meet the needs of many users, but more information is required in some important cases, particularly at the local level.

The UK does not currently have a process for systematically recording and linking the entry and exit of visitors and migrants to and from the UK. The Office for National Statistics therefore bases its main estimates of long-term (over one year) international migration on the International Passenger Survey (IPS) which is a voluntary interview survey of passengers at all main UK ports of entry. The IPS has been enhanced in various ways and produces estimates at the national level which ONS regards as robust. As with all sample surveys, however, the quality of estimates for more detailed breakdowns, such as nationality by reason for entry, is less robust because these are based on smaller samples. The Home Office is currently developing the ‘e-Borders’ system which will record the entry and exit of visitors and migrants. This will not entirely replace the IPS, as it does not record migrant intentions and will not in itself provide information on where migrants settle in the UK; but it has the potential greatly to improve the data available to ONS. ONS expects to see this improvement in the statistics beginning to be evident from 2018. In the meantime, the Statistics Authority is undertaking a broader review of the robustness of statistical estimates derived from the International Passenger Survey, as part of our published monitoring work programme. The report will be published later this year, and I will send a copy to the Committee.

2. User engagement

Again, we believe that this is mainly for the users of statistics to answer. Users told us as part of our review of migration statistics in 2009 that ONS tended to inform users about changes it was making rather than fully engaging. More recently, however, users have welcomed the more collaborative approach in which ONS has involved them in testing and assuring the quality of its new developments. Users also called for a greater use of administrative data in preparing the migration statistics. The Authority notes that ONS has recently developed a new method for the breakdown of total immigrant numbers to local authority level based on administrative sources - for use in the preparation of its sub-national mid-year population estimates.

3. Public understanding

The Statistics Authority is aware that ONS has made considerable efforts to improve both the statistics themselves and their presentation and accessibility over recent years within the constraints of the current limitations of the basic data. The Authority continues to welcome feedback from users of migration statistics in this regard, and will continue to discuss with ONS further enhancements and improvements to the presentation and commentary accompanying migration statistics. ONS has developed a conceptual framework for UK population and migration statistics that will underpin future developments. The framework will promote understanding of the concepts, data sources and processes that shape the population and migration statistics, and how they fit with the uses to which they are put. As soon as more robust data sources become available this will help ONS to take more systematic account of user needs.

The Statistics Authority is satisfied that the current migration statistics give a statistical overview of the flows of migrants to and from the UK, and that they are the best statistics that can be produced from the various sources of data that currently exist. To this extent, the Authority’s view is that the published statistics will, we believe, inform the public appropriately. However, we would want to see more robust and detailed statistics being produced, analysed and explained publicly once better administrative data start to become available.

ONS uses the United Nations’ definitions of long-term and short-term migration which have the virtue of supporting international comparability, but which do not meet the needs of all users. Some users are more interested in the permanent settlement of migrants, while others such as local authorities need estimates of the number of short-term and long-term migrants living in their areas – taking account of seasonal workers, students, and some groups of visitors for example. ONS has made progress in producing short-term immigration estimates for local authorities but is not yet able to produce equivalent emigration estimates. It is also not able to present separately the component of the migration estimates that relate to settlement.

Long-term international migration estimates based on the IPS are available by age and sex, although equivalent information is not available for other characteristics of migrants such as ethnicity, religion, language and educational qualifications. However, the 2011 Census results will provide this detail – on a one-off basis – for migrants resident in the UK in 2011. Any increase in the range of information collected in the IPS would need to be set against the costs and the risk of reducing response to the survey.

4. Uncertainty

The Statistics Authority conducted a formal Assessment of migration statistics in 2009. [3] It concluded that the statistics mainly met the standards of the Code of Practice for Official Statistics and, where there were shortcomings, these have subsequently been addressed. In that sense, the Authority is content that the estimates and their uncertainty are properly reported, although we think it would be helpful to users if further information about quality of the estimates could be provided. Uncertainty can arise for different reasons (for example, sample size or because some people are not able to answer questions accurately). By their nature, the non-statistical uncertainties – those not simply a result of sample size – are difficult to measure or to make allowance for when commenting on the statistics. ONS has started to address this through the introduction of the Migration Statistics Quarterly Report which presents administrative data alongside estimates from the IPS.

5. Migration target

It is our view that migration statistics are probably accurate enough in longer-term perspective but that, at least in the shorter-term, the net migration statistics can appear to be very volatile and it would be helpful to all observers to have more reliable net-migration estimates in the shorter term so that trends can be identified and monitored more readily. Estimates of net migration are calculated as the difference between estimates of immigration and of emigration – both of which are large, in numerical terms, and both of which are subject to their own levels of statistical uncertainty and variation from year to year. It is important for ONS to explain clearly that relatively small changes to immigration and emigration can lead to a relatively large change in net migration. The introduction of confidence intervals for net migration has been welcomed by users.

6. Improving quality

The key step, without which other steps will have only limited benefit, will be the introduction of better administrative data, particularly that from the e-Borders system. Ideally this would be joined up with IPS data, as well as from other sources, such as National Insurance Number allocations and higher education student data, to give a more complete picture. Only then would government statisticians be in a position to make major improvements. We would, however, also like to see EU and other countries working more systematically to reconcile the flows of migrants between countries. The Authority believes that this is not something that any one country can deliver on its own, but the UK might be able to stimulate further discussion in this area.


Migration statistics are used both nationally and locally by a wide range of users to inform policy and to stimulate debate. They form a key component of the Office for National Statistics’ (ONS) published population estimates which are used to assist in managing the economy, resource allocation and planning and delivery of services provided by local government and the health sector. The national ‘net’ migration figure (the difference between immigration and emigration) is used by Government and other users to monitor progress towards the current Government's migration target, as well as being widely reported by the media.

There have been significant improvements in the migration statistics produced by the Home Office, the Department for Work and Pensions (DWP) and ONS over the last five years. The Migration Statistics Improvement Programme (MSIP) [4] , a cross-departmental programme, introduced: improvements to the timeliness and frequency of migration statistics; improvements to the design and coverage of the International Passenger Survey (IPS) used to collect data on international migrants; estimates of short-term migrants coming for periods of less than a year; new methods that bring together administrative data with data from the IPS to produce estimates of both long-term and short-term international immigration for each local authority; and a Migration Statistics Quarterly Report [5] (MSQR) which brings together relevant statistics on migration from ONS, Home Office and DWP into one quarterly publication. These developments have had a substantial positive impact on the way that migration statistics are discussed by policy-makers and commentators with the debate shifting from the quality of the statistics to their content and interpretation.

1. Meeting user needs

As migration statistics contribute to policy and resource allocation decisions across a range of sectors, they come under considerable scrutiny from a range of users across Government, business and academia. Over the last decade, there has been a user demand for: improvements to the IPS to reflect the changing patterns in migration and the increased use of regional airports; increased use of administrative data to measure migration (particularly at local levels); the production of different measures of migration, in particular, short-term migrants; and improvements to the way that migration is reported so that a coherent picture of migration can be presented using sources from ONS, the Home Office and DWP.

The Migration Statistics Improvement Programme was established in 2008 to address these concerns. The Programme closed last year after delivering the following:

Improvements to the IPS

The IPS data form the basis of the official estimates of long-term international migration into and out of the UK. Improvements such as increasing the IPS sample size to identify increased numbers of migrants, including improved targeting of the sample towards emigrants, and increasing the coverage at regional airports have led to more reliable estimates of migration at both the national and regional level.

Additionally, further changes have been made to the IPS questions from January 2012, following user feedback, to identify where appropriate the original reason for migrating to the UK of emigrants. The first results from these questions will be available in the second half of 2013. These will provide information to help users better understand the immigration and emigration patterns of international students.

New methods for estimating long-term and short-term international immigration for each local authority

New methods have been developed using a range of administrative data, together with the International Passenger Survey data, to estimate both the long-term and short-term international migrants for each local authority. These are now being used in the production of sub-national population estimates and projections which are used in the allocation of resources from central government to local authorities. [6]

The Migration Statistics Quarterly Report (MSQR)

The MSQR was introduced in 2009. It brings together and summarises the international migration statistics which are available from across Government. It provides the latest figures on who is migrating, why people are migrating, and where they are migrating from (or to). Additional summaries have been produced for users on short term migration, emigration, students, work, family, European Economic Area (EEA) migration, migration from countries that acceded to the European Union in 2004, and population by nationality and country of birth. These additional summaries provide users with information on topics of interest, including links to underlying data.

The level of detail provided in published migration statistics outputs has been developed in response to consultations and discussions with users. In recent years, a range of users from the public, media, academia and special interest groups, to local and central government, have provided comments on the level of detail that would be useful to them. The following changes have been made since 2009 in response to this feedback:

· A streamlined MSQR publication has been produced, structured to provide the key messages and focus on the characteristics of migrants, why they are migrating and where they are migrating to or from;

· Increased information has been provided on reliability with the introduction of confidence intervals on survey-based outputs;

· More detail published on Long Term International Migration;

· More detail published on local area migration through the Local Area Migration Indicators [7] ;

· Enhancements made to quarterly charts designed to more quickly and succinctly provide the key messages;

· Underlying data published about migrant ‘stocks’ including nationality and country of birth at local authority level;

· Reports on emigration and population by country of birth and by nationality;

· Innovative data visualisation tools such as a migration timeline, published on the ONS website;

· Topic reports published by the Home Office on work, study, family and EEA migration;

· Summary reports published by ONS on particular topics including Polish-born residents in the UK and on new Census-based migration data; and,

· Further expansion of the availability of published Home Office data on migration.

Migration statistics are accessible via the UK National Statistics Publication Hub and via the MSQR publication on the ONS website, which contains links to underlying data sets and other reports (such as Home Office topic reports). Users are notified of latest releases via a dedicated email list and via social media platforms. Data can also be accessed via the data.gov.uk website. Contact details are provided on all migration statistics outputs as required under the Code of Practice for Official Statistics, and ONS deals directly and promptly with queries received from a wide range of users.

User feedback to these improvements has been positive. For example, the Migration Statistics User Forum (MSUF) commented that the MSQR has enabled users to focus on the messages arising out of the statistics rather than establishing which figures to use.

2. User engagement

Producers of migration statistics pro-actively engage with users and regularly present at various user events such as the British Society for Population Studies conference, the MSUF, and the Royal Statistical Society. A virtual online community was set up which is used to alert users to consultations and the release of new statistical outputs.

The feedback provided by users has resulted in improvements to the way that the statistics are collected and disseminated, and some of these have been outlined above. Other examples include:

· Changes to the Census. New migration-related questions were added to the 2011 Census household questionnaire following consultation with users. These will provide comprehensive, small area information on nationality and citizenship as well as providing information on the length of time non-UK born residents have been in the UK. This will also provide a clearer view of different types of migrants (such as short-term migrants) resident at local authority level. As more Census data is released on the characteristics of migrants, detailed analysis will enable the socio-economic outcomes of migrants, such as their labour market status, to be compared across different groups of migrants.

· Provision of detailed information in published tables. Users requested more information on individual countries of birth and nationalities that were not in published tables. ONS responded to this by publishing underlying data on population stocks for the first time in August 2012.

· Provision of quality information. ONS has recently published a report [8] on the quality of the IPS for measuring international migration flows. This has provided users with further detail on the quality of the IPS, including response rates, coverage and the confidence intervals that accompany key migration statistics.

The Home Office has taken a range of actions to meet the requirements of the Authority’s Assessment of published migration statistics through improvements in respect of its migration statistics outputs, such as providing more information on data quality alongside improvements to presentation. These were implemented in the May 2012 and August 2012 editions of the MSQR.

DWP produce supplementary migration statistics sourced from National Insurance Number ( NINo ) allocations to non-UK nationals entering the UK. While not an explicit measure of migration, they do provide a rich source of supplementary data about migrants’ nationality and about where they live on arrival in the UK. The UK Statistics Authority assessed these statistics in 2011 and DWP responded to the requirements arising out of the Authority’s Assessment by making improvements to the relevant pages on the DWP website, by releasing improved metadata, in developing improved tools for disseminating these data, and by undertaking a user consultation on the statistics earlier, for which a consolidated response has been published.

In January 2011, DWP released ad-hoc statistical analyses about the nationality of working age benefit claimants. This report was produced by drawing together a range of administrative data to improve the evidence base. In future, DWP intend to record the nationality of migrants making claims to receive the new Universal Credit.

3. Public understanding

The MSQR includes a ‘Summary’ section which presents key messages in a short, easy to understand format for users. These messages are also often directly quoted by the media.

The Authority has confirmed designation of National Statistics status to the Home Office, DWP and ONS data indicating these meet identified user needs, and ONS has consulted users to ensure that this continues to be the case.

4. Uncertainty

Confidence intervals are now published for net migration, as part of the MSQR, and continue to be published for immigration and emigration. ONS has also published a paper [9] providing more information about the methods used to calculate confidence intervals as well as guidance on how confidence intervals should be interpreted. The independent Migration Observatory at Oxford has also released on its website a useful guide [10] to the confidence intervals and how these could be interpreted in light of the Government’s migration target.

The extent to which increasing the sample size of the IPS will lead to improvements in the reliability of migration estimates has been discussed, including by users. 800,000 passengers travelling through UK ports of entry are approached each year as part of the IPS to identify whether or not they are a migrant. This sample currently identifies approximately 5,000 passengers who are long-term international migrants. To increase the accuracy of estimates further would require significant financial investment. For example, the 800,000 sample would have to be increased fourfold to reduce the size of the confidence interval by approximately 50 per cent.

The IPS achieves excellent response rates for a voluntary survey with a respondent refusal rate of less than two per cent. The improvements made to the IPS from 2009 have resulted in lower standard errors (the measure of uncertainty surrounding an estimate derived using a sample survey) suggesting that the reliability of the IPS has improved.

The Home Office has improved the way it publishes revisions of its key migration estimates. For example, they have published an analysis which shows that most revisions for these migration estimates are small. The analysis also provided an explanation for the small number of substantial revisions.

5. Migration target

Estimates of net migration, which are based on information from the International Passenger Survey, are used by Government and other users to monitor progress towards the Government’s migration target. As with data derived generally using sample surveys, the net migration figure is subject to uncertainty and confidence intervals are published alongside the estimates of net migration to show this uncertainty. Presenting confidence intervals for users is recognised as good statistical practice with survey data. Some users have expressed the wish that the uncertainty around the net migration estimate was less but there would be significant resource implications if this was to be achieved through the IPS.

6. Improving Quality

ONS believes that the improvements discussed above have resulted in better quality migration estimates at both the national and regional level and that this is recognised by users.

Quality could theoretically be further improved by increasing the sample size of the IPS but, as indicated above, this is not a feasible option for achieving significant improvements in the reliability of detailed IPS estimates. ONS’s current view is that existing quality levels are sufficient to meet the majority of users’ needs and policy-making at the national level, and therefore the cost of increasing the IPS sample might outweigh the potential quality gains.

It is already anticipated that e-Borders data will be incorporated into migration estimates reporting in the future, subject to data quality investigations and the development of methods, and this will deliver further benefits. These benefits are expected to include:

· Providing more robust estimates of long-term and short-term migration counts at the national level which will not be subject to the same levels of uncertainty due to sampling. However, this can only be achieved when there is complete coverage of e-Borders which is not expected until 2018;

· The potential of using e-Borders data to "weight" the IPS sample to provide national estimates in the short term; and

· Providing greater information on population and migrant movements. For example, it could be used to measure circular migration where a migrant makes several short-term visits to the country. [11]

However, e-Borders data will not be able to replace the IPS fully because it will not collect some of the key information that users require, for example respondents’ reasons for migrating and where migrants intend to stay when they enter the UK.

January 2013

[1] http://www.statisticsauthority.gov.uk/reports---correspondence/reports/authority-report-4--migration-statistics-the-way-ahead.pdf

[2] http://www.statisticsauthority.gov.uk/reports---correspondence/correspondence/letter-from-sir-michael-scholar-to-rt-hon-keith-vaz-mp-11072011.pdf

[3] http://www.statisticsauthority.gov.uk/assessment/assessment/assessment-reports/assessment-report-8---migration-statistics--27-july-2009.pdf

[4] Migration Statistics Improvement Programme Final Report, http://www.ons.gov.uk/ons/guide-method/method-quality/imps/latest-news/msip-final-report/migration-statistics-improvement-programme-final-report---download-file.pdf

[5] http://www.ons.gov.uk/ons/rel/migration1/migration-statistics-quarterly-report/november-2012/msqr.html

[6] More information on this method is available at http://www.ons.gov.uk/ons/guide-method/method-quality/imps/improvements-to-local-authority-immigration-estimates/index.html.

[7] http://www.ons.gov.uk/ons/rel/migration1/migration-statistics-quarterly-report/august-2012/migind.xls

[8] http://www.ons.gov.uk/ons/guide-method/method-quality/specific/population-and-migration/international-migration-methodology/international-passenger-survey-quality-information-in-relation-to-migration-flows.pdf

[9] http://www.ons.gov.uk/ons/guide-method/method-quality/specific/population-and-migration/international-migration-methodology/international-passenger-survey-quality-information-in-relation-to-migration-flows.pdf

[10] http://www.migrationobservatory.ox.ac.uk/commentary/entries-exits-and-errors

[11] More information on these benefits is described in further detail in ONS's report: Delivering Statistical Benefits from e-Borders: http://www.ons.gov.uk/ons/guide-method/method-quality/imps/latest-news/delivering-statistical-benefits-from-e-borders/delivering-statistical-benefits-from-e-borders---download-file.pdf .


Prepared 4th February 2013