National Statistical

Not only is the population changing in size and structure, the way we measure it is also changing. Mary Gregory explains what is driving population growth and the progress the Office for National Statistics is making to continually improve our population estimates so they best meet user needs.

The population of England and Wales continues to grow. Although increasing at a similar rate to the previous 12 months, the year to mid-2023 saw the largest annual increase in at least 75 years, growing by almost 610,000 to 60.9m.

There are three components of population change – births, deaths and migration; migration includes international and cross border with other parts of the UK.

The record levels of international migration in recent years have been the main driver of population growth. But the year to mid-2023 also saw an increased number of deaths, expected in an ageing and growing population, as well as the lowest number of births since 2002.

In fact, in the most recent year, natural change (births minus deaths) was only at plus-400, the lowest reported figure since 1978. And, interestingly, deaths outnumbered births in every region, with the exception of London and the West Midlands.

Fertility rates, which measure the number of children born per woman of childbearing age, have been gradually falling across the world and more than halved since 1963. In England and Wales, it is now 1.49 children per woman, down from a peak of just under three in the 1960s.

Understanding all these components of population change is vital, with population estimates and analysis among the most critical outputs produced by the ONS. They inform decisions by governments and others; for example, making sure schools are in the right places, ensuring social care is delivered to the right people in the right areas and knowing where to place NHS services. They also underpin many other statistical outputs, such as survey weights or denominators.

Transforming our statistics

Later this year, we plan to make our recommendation on the Future of Population and Migration Statistics.

Regardless of the recommendation and what it might mean for a decennial census, we are already transforming the way we produce our regular migration and population statistics to make greater use of administrative data (information created, and then collated by government, when people interact with public services) – as explained in our statistical design paper.

Since the pandemic, our migration statistics have switched from using an intentions-based survey to producing estimates based primarily on actual behaviours observed in admin data, such as visa data and tax records, so we can better understand who is actually coming to and leaving the country.

Today, we’re also sharing our progress towards admin-based population estimates (ABPEs). We’re sharing these to help users understand the new approach, share their feedback with us, and take time to consider what it means for them before we move to the ABPEs as our official estimates of the population.

For mid-2023, our mid-year admin-based population estimates are very similar to our accredited official mid-year population estimates; the total ABPE for England and Wales is just 0.2% lower than the accredited mid-year estimate.

The mid-year ABPEs published today are an improvement on what we have previously published. They incorporate updated migration estimates and deaths for mid-year 2023 alongside improvements to the coverage of some of the other sources. We’ve also continued to strengthen the tools and processes we use to thoroughly assure the quality of the estimates.  We will do further work to understand and explain what is driving the differences between our old and new methods, especially working with local authorities to understand their data.

What are ABPEs?

We have typically had a census every 10 years. That census is like a giant stocktake of the population. But a lot can change between censuses. Our traditional mid-year population estimates use the census as a starting point and each year we add births, take away deaths, and account for internal and international migration – it is sometimes referred to as the cohort component method. However, as you move further away from census year, we know the estimates drift away from the real figure.

Let me give you an example. Imagine a town – let’s call it Statsville – built 2,000 new homes in 2022. That’s one year after the census. People move into those homes from neighbouring areas. Under the current approach we measure internal movements using NHS data, so we will only pick up those moves once people have interacted with the NHS. Some may do so quickly, some may not register a change of address for years. We only know if we’ve accurately picked up all of those movements at the following census.

The developing ABPEs use more administrative sources linked together (such as health, tax and education records) to create a stock estimate for each local authority based on the most recent sign of administrative activity, rather than relying solely on the internal migration estimates derived from health data.

So, rather than wait ten years to see everyone who has moved to the new housing estate in ‘Statsville’, these additional data sources can help us see actual behaviours in nearer to ‘real time’. Eventually, we hope, by using multiple data sources, we can have an on-going stocktake of the population, to balance against flows into and out of the country, and internally from place to place.

The way we are able to bring these different data sources together in a meaningful way is via the Dynamic Population Model (DPM). The DPM balances all this information, which has been de-identified in a secure environment, to provide a coherent set of demographic accounts. You can read more about that here.

Next steps

These ABPEs are at a research and development stage, and we caution against using them for decision making purposes.

However, our intention is for them to become our official measure of the population in 2025. This will be dependent on meeting the acceptance criteria we will publish later this year and take into account the feedback we receive following engagement.

Pivotal to delivering these new methods is securing a sustainable supply of quality admin sources, including the continued supply of data we already use. We are also investigating new data sources for use in the future. For example, we are exploring how we can better understand people’s mobility, which may come from a variety of sources, including mobile phone location data or tax and benefits records.

It is a priority for us to work in partnership with the Devolved Administrations, so we can develop coherent population estimates for the UK that take account of our new methods.

We will work with users to understand what information they need to support confidence in the new approach. We will continue to evolve what we publish to support these needs. This includes being clear about the quality of the sources we use and the uncertainty of the estimates we produce. Our updated quality strategy explains this more.

We are also working with the Office for Statistics Regulation to seek accreditation of the ABPEs, and our long-term international migration estimates.

Our ability to produce the best estimates is informed by the feedback we get from those who use our data. So please do get in touch if you have any comments on our plans. You can email pop.info@ons.gov.uk.