1. Introduction

Office for National Statistics (ONS) is transforming the way we produce population and migration statistics, to better meet the needs of our users. Working in partnership across the Government Statistical Service (GSS), we are progressing a programme of work to put administrative data1 at the core of our evidence on international migration (UK) and on population (England and Wales) by 2020.

This ambition is based on our current plans for acquiring access to the further administrative data sources we need to deliver this. Our work programme is also an integral part of the work over the next four years to make a recommendation to the UK government in 2023 about the future of population and housing censuses in England and Wales.

We have long acknowledged that the International Passenger Survey (IPS) has been stretched beyond its original purpose and that we need to consider all available sources to fully understand international migration. Users have also told us that they want to have a coherent understanding of what different data sources tell us and how they compare, including other administrative data and survey sources across government.

In our research engagement report published on 30 January 2019 we indicated that we will carry out further work to compare what existing survey sources tell us about population and migration, including the IPS, the Labour Force Survey (LFS) and the Annual Population Survey (APS).

This note sets out some comparisons between the sources that highlight the issues. While they are not directly comparable for a number of reasons, there are differing patterns for EU and non-EU citizens, and the latest LFS data suggest a different trend. This note also sets out the workplan we have put in place to further investigate these differences within the context of our wider transformation plans. This context is important, as our work with administrative sources may reveal insights that help us make sense of the survey data.

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2. Background

In December 2016, we published an article explaining the definitional differences between Long-Term International Migration (LTIM) flows produced using the International Passenger Survey (IPS) and the change in the estimates of the non-UK born population measured by the Annual Population Survey (APS).

In theory, the change in the number of non-UK born people living in the UK from year-to-year should be close to the net flow of non-UK born people into the UK. However, the two surveys are designed to measure different things, in different ways, based on different types of data, and neither has complete coverage. These differences are reproduced from our 2016 article in Annex A.

Since we published that article, the IPS, APS and Labour Force Survey (LFS) series appear to have continued to diverge, with the annual changes in APS stocks showing a highly variable pattern. This can be seen in Figures 1 and 2, which show a comparison of LTIM net migration estimates and annual changes in APS estimates of the non-EU born and the EU born populations.

In addition, the latest LFS data show that the non-UK born population could be falling (Figures 3 and 4).

When the cumulative effect of the difference between LTIM net migration and the annual differences in APS estimates of the population is explored we can see in Figures 5 and 6 how the EU series has been diverging since 2005, whereas the non-EU series only began to diverge after 2011.

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3. Workplan

The workplan set out in this section is designed to build on the work published in December 2016, bringing the analysis up-to-date. The overall aim is to explore what is going on in each of the surveys to understand the differing patterns seen in the data and to identify potential areas where the data sources may be strengthened. This could be achieved either directly in the survey itself, or by bringing a range of sources together to strengthen the outputs.

One area that we are keen to investigate is how outliers may have impacted on the survey estimates and the extent to which this may have caused some of the observed volatility.

We intend to hold a workshop with migration experts later in the spring to explore our initial findings and to challenge assumptions about the different sources that may influence interpretation or conclusions based on these.

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4. Next steps

We intend to publish an initial update on the progress of this work in spring this year, with a fuller assessment later in the summer.

Please send any feedback on this workplan to pop.info@ons.gov.uk

Please indicate in your response if you do not wish for the Centre for International Migration (ONS) to keep your details. Your personal information will be stored and processed securely as outlined in the Privacy information for our stakeholders document.

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5. Annex A: Differences between sources of stocks and flows data

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Contact details for this Article

Ann Blake
Telephone: +44 (0)1329 444097