1. Our mission – why transform?

It is our mission to provide the best insights on 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 decline 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 impact on 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 statistic 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

Developing our approach for producing admin-based population estimates

We have continued the research outlined in our previous publication, using activity-based rules and records from single and linked data sources to develop our approach for producing admin-based population estimates. Initial rules have been combined to produce the first admin-based population estimates (ABPE) using this approach. These rules have largely removed patterns of overcoverage 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 overcoverage. 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.

Understanding different migration data sources

The Understanding different migration data sources: June 2019 progress report explores the differences between different outputs that relate to international migration, in particular, the International Passenger Survey based long-term international migration estimates, and outputs based on the Annual Population Survey and the Labour Force Survey. Our findings show that a range of factors (such as coverage of source and survey issues) impact the coherence between these outputs, and the impact of those factors accumulate in combination.

This research highlights main population groups that we need to explore in our current sources and in our administrative data research, and we will provide further insights later this year.

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 putting a spotlight on what different administrative data sources tell us about international migration.

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6. What’s 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 further work explaining the coherence of different sources on international migration (as set out in our workplan)
  • Our design for putting administrative data at the core of population and migration statistics in 2020 and beyond
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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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