1. Our mission – why transform?

It is our mission to provide the best insights into population and migration using a range of new and existing data sources to meet the needs of our users.

The current population system is heavily reliant on the decennial census. While this provides granular data at the lowest levels of geography every 10 years, it delivers less detail throughout the interim years. Additionally, the quality of our population estimates declines as we move further away from the census year. Transforming this system to one led by administrative data offers the opportunity to provide more frequent statistics and new analysis that better meet user needs, as set out in our previous work on the Administrative Data Census project.

A rapidly changing policy context – including the government’s plans for a new immigration system once the UK exits the European Union – offers us a well-timed opportunity to reflect on the best way to deliver the population and migration statistics system to best meet user needs. Enabled by data-sharing powers in the Digital Economy Act 2017, we have the opportunity to make use of more data. This is essential to better understand our fast-changing population at both national and local levels, and the wider policy impact and context.

We have long acknowledged that the International Passenger Survey (IPS), which underpins our existing international migration estimates, has been stretched beyond its original purpose and that we need to consider all available sources to fully understand international migration. Additionally, there is no single, comprehensive data source that tells us everything about the population. Therefore, our approach focuses on identifying the strengths of individual data sources, integrating them to give us a much richer understanding of how our population is changing. To help meet these new challenges, the Office for National Statistics (ONS) has developed a set of data principles to guide our data principles and management. These underpin all the work we do, ensuring security and building trust.

Taking a fresh look at how we can produce our population and migration statistics also offers us the opportunity to be more responsive to user needs and provide more coherent statistics.

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2. Why are these statistics so important?

Population and migration statistics underpin a wide variety of other statistics (such as unemployment rates) and inform a vast range of decisions. For example, the ability to accurately forecast pensions, make decisions about local services (such as the number of school places or the provision of health services for an ageing population) and decisions about where to site new businesses. These statistics are also used to help inform public debate. It is therefore essential that these statistics are accurate and timely.

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3. How are we transforming population and migration statistics?

Working in partnership across the Government Statistical Service (GSS), this transformation work brings together what we have previously published through both the Office for National Statistics (ONS) Administrative Data Census project and the cross-GSS Migration Statistics Transformation Programme.

We have set ambitious targets to put administrative data at the core of our evidence on international migration and population by 2020 and will deliver a predominantly online census in 2021. The ambition is to deliver a fully transformed system for producing population and migration statistics by 2023. It is important that work done between now and the delivery of outputs from the 2021 Census paves the way for continuous improvement and supports the ambition that “censuses after 2021 will be conducted using other sources of data”. Most importantly, the outputs that we publish should be coherent and meet the needs of our users.

For this reason, we have taken the decision not to benchmark the Administrative Data Census outputs with the outputs from the 2021 Census. Instead, we will ensure that we use the best available sources to produce the best-possible outputs from the census, and to put administrative data at the core of our population and migration statistics system. We will iteratively develop our transformed population and migration statistics system, taking on board feedback from users and making the best use of new data, and new methods as they become available. We will rigorously quality assure new methods and share the impact of any changes made, demonstrating the benefits and improvements before implementing them.

This work programme is also essential to providing evidence to inform the recommendation to the UK government in 2023 about the future of population and housing censuses in England and Wales.

To make sure that our transformation journey is as open and transparent as possible, we will:

  • regularly publish research and methods as we develop them

  • continue to present analysis showing the coherence between different sources of information

  • engage with our users and stakeholders, seeking regular feedback

  • use our research findings, the best available data and methods, and the feedback from users to make decisions about which improvements to make each year

  • implement changes to our statistics when and where appropriate, clearly communicating these changes to users in advance of making them

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4. What have our users told us?

Our users sit at the heart of our framework for transforming these statistics (Figure 1), which describes the important questions we need to answer to meet their needs.

We know from when we have previously engaged with our users that they need us to provide coherent statistics on the size (or stock) of the population, and how it changes over time (flows, both nationally and locally). We also need to tell a clear story about what is contributing to this change and show how different groups in the population affect society and the economy, including on our workforce, communities and public services such as the NHS and schools. This needs to be recognised as the story that is being experienced by our users.

Our users have also told us that they want us to deliver these statistics frequently, and in a timely manner to be able to make evidence-based decisions. Our statistics also need to be relevant in a rapidly changing society, and we need to be able to report on their quality.

We are constantly seeking feedback to shape the direction of our research and to improve our approach. When we asked for feedback following our report published in January 2019, users told us that we were on the right track but challenged us to provide more evidence to ensure we instil confidence in these statistics. The feedback we received shows support for how we are reviewing current data sources and looking to maximise the value of administrative data in future.

A full summary of the user feedback is available.

How can users get in touch?

If you would like to get in touch, please contact us by email at pop.info@ons.gov.uk.

You can also see us at the following events:

We are also working with local authorities, experts from academia and other government departments through invited engagement groups to help shape and quality assure our work. Additionally, we are engaging with other National Statistical Institutions (NSIs) across the UK and internationally to share experiences and seek feedback on our plans.

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5. Main messages from our latest research

Migration statistics tables – we need your feedback

On 21 August we published our latest Understanding different migration data sources report. This set out the conclusions of our research into the coherence of migration data sources including the International Passenger Survey (IPS) and the Annual Population Survey (APS) alongside other administrative data sources. Based on these findings we made preliminary adjustments to the headline measures in the latest Migration Statistics Quarterly Report (MSQR) to provide our best possible assessment of migration. These adjustments only have a small impact on UK net migration and the trends we see over time are largely unchanged. This is because the adjustments made to the EU and non-EU figures broadly cancel each other out. To reflect our transformation journey and the period of development and innovation that the statistics are undergoing, we have reclassified our migration statistics as Experimental Statistics.

When we made the preliminary adjustments to the headline measures, we were only able to adjust the highest level tables that we publish alongside the MSQR. We understand that our customers would like to see the more detailed tables adjusted where appropriate, and are currently working through what is feasible for the November release. This is particularly important as the November release is when we normally update all our most detailed annual tables.

In assessing feasibility we will consider whether we are able to incorporate the adjustment into the detailed tables, but also whether it makes sense to do so at that level of detail. We will also consider the quality of the most detailed tables and the information we have on how often they are used. This will allow us to evaluate whether it is sensible to continue to produce those tables.

We are keen to gather feedback on which tables users think are most important for us to adjust. We would also like to know what users think the most important factors to be considered are while undertaking this review. Please contact us at pop.info@ons.gov.uk by 24 October 2019 to share your views.

We will test our proposals with our wider Government Statistical Service (GSS) colleagues and expert stakeholders through our GSS Migration Statistics Working and Steering Groups, the UK Population Theme Advisory Board and our Expert Group on Migration Statistics. Following this we will publish our proposals in an update to this article ahead of the November Migration Statistics Quarterly Report.

International migration and the health sector

On 15 August 2019, we published our analysis plans on the contribution and impact of international migration on the health sector. This article looks at migrants both as a workforce and users of public services. We set out our plans to provide better evidence and fill some of the evidence gaps, drawing on all available data sources as no single source gives us a definite picture.

Alongside this, we published a report on international migration and the healthcare workforce. This draws on all currently available sources and provides a summary of the insights we can obtain from these sources. We set out how many migrants work in healthcare in the UK and explore their age structure, location and changes over time. We also present data on specific health workers in England, such as hospital nurses and general practitioners.

Migrant labour force within the tourism industry: August 2019

On 15 August 2019, we published our analysis of migrant labour force within the tourism industry. This analysis uses official data sources to look at the current composition of the overall tourism industry and considers movements of people into and out of the tourism industry over time. Between 2016 and 2018, there was an average of 3.2 million people working in tourism. The tourism sector has a higher proportion of non-British nationals (16%) when compared with all other sectors (11%).

Providing a better understanding of the migrant workforce is one of the ways we are mobilising the power of data to help Britain make better decisions.

Understanding different migration data sources

The Understanding different migration data sources: August 2019 progress report sets out how we can draw on the combined strengths of survey and administrative sources to provide a better understanding of international migration.

Our latest research builds on the June 2019 progress report which investigated the divergent patterns in what the International Passenger Survey (IPS) and the Annual Population Survey (APS) tell us about migration. It also draws on our previous research reports that used administrative data to provide additional insights on aspects of migration.

When we look over an extended time period (2005 to 2018), there is a divergence in what the IPS and APS tell us about long-term international migration in the UK. Definitional and survey differences – including coverage of communal establishments and deaths – only explain part of this divergence. The most likely cause of the remaining divergence is the impact of certain groups having a higher degree of uncertainty in their intentions to move to and from the UK.

To get the best overview of trends in migration, we need to look at all available data sources. To help address the impact of uncertain intentions for non-EU students at the end of their studies and for EU8 nationals moving to the UK, we apply preliminary adjustments to our IPS estimates based on data from the Home Office and Department for Work and Pensions – which tell us about people’s actual behaviour. Overall, we find these preliminary adjustments only have a small impact on UK net migration and the trends we see over time are largely unchanged, giving us confidence in our previous headline estimates.

For EU migration, we made a preliminary adjustment up to March 2016, which draws on the strengths of what the Department for Work and Pensions data tells us about immigration from EU8 countries. For non-EU migration, we made a preliminary adjustment up to 2018, drawing on the strengths of what Home Office data tells us about emigration of non-EU students.

This work has shown the importance of our transformation programme in providing the best possible assessment of international migration based on all available sources. As new data sources become available, we will build on our research so far and continue to develop our approach for adjusting the IPS estimates to take account of uncertain intentions. This includes strengthening our understanding of changes to patterns since 2016. Working across the GSS, we will investigate whether there are other available administrative data sources that provide further evidence to refine our preliminary adjustments.

How we are making the best possible assessment of migration

Bringing these research findings and the available data sources together, we have made preliminary adjustments to our headline measures of migration to provide our best possible assessment of trends over time. These preliminary adjustments are reflected in the latest estimates in the MSQR, published 22 August 2019.

While we go through this transformation journey, we have sought to re-classify our migration statistics as experimental statistics in line with Office for Statistics Regulation guidance. Re-classifying to experimental statistics supports this period of development and innovation, and is reflected in the latest MSQR published 22 August 2019. We expect our current work programme to be complete by this time next year when we will seek re-designation to National Statistics status.

Developing our approach for producing admin-based population estimates

On 21 June 2019, we published our analysis using activity-based rules and records from single and linked data sources to develop our approach for producing admin-based population estimates. This builds on research outlined in our previous publication. Initial rules have been combined to produce the first Admin-Based Population Estimates (ABPE) using this approach. These rules have largely removed patterns of over-coverage seen in previous research. While this now results in higher levels of under-coverage, this is much more comparable with the results seen from the census before adjustment takes place.

There is potential for this method to be improved to reduce the amount of coverage adjustment required. Access to additional data sources and more sophisticated rules should allow more records to be added where there are currently deficiencies, without increasing the levels of over-coverage. This means any adjustments will be from a better starting point than the census. We will also continue to develop this method to provide analysis at the local authority level.

This provides a platform for combining with a Population Coverage Survey to produce coverage-adjusted estimates in a similar way to the method used to successfully adjust the census.

Measuring illegal migration

A short note outlining our discussions on the measurement of illegal migration has also been produced and published.

Update on our population and migration statistics transformation journey

In January 2019, we published a research engagement report updating our users on our population and migration statistics transformation journey. This showed the progress we have made by bringing more sources together to fill gaps in coverage and presented a series of case studies identifying what different administrative data sources tell us about international migration.

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6. What is next?

We will be updating our users later this year on:

  • our administrative-based flows research and our work exploring concepts and definitions for population and migration statistics

  • our design for putting administrative data at the core of population and migration statistics in 2020 and beyond

  • our approach for assessing our progress on our transformation journey

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7. More about our transformation journey

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8. More about our official population and migration statistics

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Contact details for this Article

Becky Tinsley
Telephone: +44 (0)1329 444661

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