Ensuring our population statistics meet the needs of everyone

The impact of the pandemic and Brexit means there has never been a greater need to understand changes in our population. In this blog Rich Pereira explains some priority areas for our population estimates and projections, on-going user engagement and our response to the recent Office for Statistics Regulation review of our population statistics.

Next year the first results from Census 2021 will be published. They will not only provide information on our population and our health – they will also shed light on social and economic changes to our lives. While they will provide us with new information that we will be able to use for years to come, we know that local authorities and stakeholders are keen to see more timely data to meet their needs.

These numbers – and subsequent detailed statistics – will also provide the baseline of population statistics for the months and years to come. Our mid-year estimates for 2021, published next summer, will be based on the new census data, as will our population and household projections which follow.

As Sir Ian Diamond, National Statistician, pointed out this spring, the pandemic has revolutionised data and there is no turning back. The census will enable us to provide excellent population estimates from which the pandemic recovery can be planned. With fresh data from 2021, we will be able to update the analyses we have already done and use it alongside new data sources to give us the richest data we have ever had.

But that’s not to say the ONS is waiting for these results to give the most up-to-date picture of the population. We have already been making some important changes to ensure our data is as timely, accurate and useful as possible.

What we’re doing now

In April we published early indicators of the UK population, which provided important insights on the size and age structure of the UK using the latest available data. These were followed by our mid-year population estimates in June, which provided more detail at a local level.

We have reweighted our labour force survey and in September will publish our population by country of birth and nationality statistics, which will give us the best picture of our foreign-born population right up to the end of 2020.

Since May we have been engaging with the Office for Statistics Regulation following its review of our population estimates and projections and today have set out how we intend to progress our work over the next 12 months.

The review was initiated in response to concerns raised with OSR in November 2020 regarding the population projections and mid-year population estimates for Coventry.

We welcome the recognition in the report that the ONS is at the forefront of addressing the complex challenge of measuring the population using internationally recognised methods and sources and we recognise the need to keep these current and responsive.

We are committed to producing the best estimates of the population and will continue working with users of our statistics to ensure we are doing just that. Local knowledge is crucial to our understanding of change that might be occurring and we will continue developing our methods to incorporate these insights.

There are several areas where work is already well underway, including on-going engagement with users of our data, as well as focus on the specific impact of students and migration on population estimates.

Understanding the movement of students

One area of particular challenge in recent years has been around the ONS’ counting of students. In areas such as Coventry, Canterbury and Cambridge, campaigners have argued that over or under counting of students has impacted the accuracy of population estimates and projections in cities with a large proportion of students.

The ONS has long recognised that the movement of students presents a specific challenge in our population – and migration – estimates. As part of the OSR review, we plan to complete detailed case studies on cities with large student populations.

When Census 2021 data becomes available, we will seek to use this to understand implications for mid-year population estimates and projections for cities with large student populations. Ahead of this we will review how recent work using administrative sources (for example, Home Office Exit Checks, Higher Education Statistics Agency and Pay As You Earn data) can provide insights on student population movement in to and out of local areas and explore how student populations change in combination across our population estimates and projections.

We will share insights with experts and consider any further areas which need to be addressed with regard to our measurement of cities with large student populations.

Transforming migration statistics

Historically, our key measure for how many people immigrated into or emigrated out of the UK, the International Passenger Survey (IPS), was paused in March 2020 due to the coronavirus pandemic.

We’ve previously stated our intentions to measure international migration using administrative sources, including Home Office visa data. This work remains challenging due to coverage gaps in the data, for example students. In the future, our work on administrative based migration estimates will be supported by statistical modelling, which we’ve developed over the past year to help plug those gaps.

Modelling of international migration allows us to produce timely population estimates and is consistent with our wider ambitions to transform population and social statistics. We’ll have further updates on this later in the year.

We want to hear from you

As we address the recommendations made by OSR we will continue to provide updates on the findings from the work we complete and resulting changes to our processes and plans so all users are aware of the changes we make.

ONS continues to welcome feedback on the planned approach we have outlined to respond to the OSR review and on our statistics and methods. Please provide feedback to us at pop.info@ons.gov.uk

The Census 2021 outputs consultation has also begun. We will be looking at the detailed needs for data and analysis, to ensure the data produced helps to answer the most important questions facing our society. Most importantly, we want to hear from users on their need in topic areas that may be subject to rapid change since the latest census.

The users of our statistics are at the heart of what we do. Your feedback will influence our future plans and help us provide the data and insights the UK needs.


Rich Pereira is the Deputy Director, Centre for Ageing and Demography