Mid-year population estimates for England and Wales

Overview

At the time of this report, the Office for National Statistics (ONS)’s national and subnational 2024 mid-year population estimates (MYEs) for England and Wales are published as accredited official statistics.

These statistics provide the official headline measure of the population in England and Wales on an annual basis. The statistics are used extensively by a wide range of users for different uses. They provide insight into the size and location of the population and feed into a range of other datasets, for example to calculate employment, unemployment and inactivity rates in labour market statistics. In turn, MYEs are used to underpin important operational and policy decisions, both at a national and local level.

This review assesses the extent to which the MYEs continue to meet the standards of Trustworthiness, Quality and Value of the Code of Practice for Statistics. In parallel we sought user views on ONS’s development of the admin-based population estimates (ABPE).

Why we did this review

In 2021 we initiated a review in response to user concerns raised with us regarding the population projections and mid-year population estimates for Coventry. The concerns were about the perceived inaccuracies of the population estimates on which the household projections and subsequent housing need are based. We concluded that ONS needed to build and enhance its approach in three ways: improve methods; enhance communication; and embrace challenge. Our 2021 recommendations set out areas for ONS to address.

In parallel, ONS has been developing new ABPEs using the dynamic population model, a Bayesian statistical modelling approach, to improve the way it measures the population. Development work for the new methods has rapidly increased in recent years, as part of considering alternative options to a 2031 census. To support ONS’s ambition, we conducted the first phase of an assessment of the ABPEs in 2024, focusing on the quality aspects of the new approach. Since then, ONS has used our findings to help steer and shape its developments.

ONS set out its ambition to transition from the current traditional cohort component method used to compile its annual MYEs to the ABPEs as its headline official measure of the population in summer 2026. We wanted to assure ourselves and users around the quality of the traditional MYEs, as the continued headline measure. This was reinforced by user concerns raised during our 2021 Census in England and Wales phase 3 assessment report. ONS has since made the decision not to transition, and instead to focus on improving the MYEs.

Highlighted findings

ONS’s decision not to transition to admin-based population estimates (ABPEs) in 2026 provides a valuable opportunity for ONS to focus on continuous improvement of the existing mid-year estimates (MYEs).

The current MYE methods have known limitations, particularly regarding the measurement of internal migration and disaggregation of international migration at the local authority level – issues which contributed to past concerns.

At a national (country) level, the population estimates are of sufficient quality that means that they meet their intended uses. User confidence is generally strong at the national level.

Census 2021 took place during the COVID-19 pandemic. The impact this had on population movement at a local level presents challenges for some users as a baseline in subnational population estimates.

Some users raised significant concerns with the quality of subnational and subpopulation estimates. We share these concerns and consider them credible, given the well-established challenges in producing reliable estimates for areas with high population churn. Local authority intelligence indicates an over- or under-estimate in some areas. These discrepancies are yet to be fully explained and are indicative of a need for ONS to innovate and improve its methods.

There is a need for clearer communication and guidance to strengthen user confidence – particularly around quality, uncertainty, revisions and how different population estimates should be used – helping ensure the statistics remain trusted and relevant.

Our user engagement exercise found that while many users value the accessibility, clarity and granularity of ONS’s population statistics – particularly the quality of written guidance and the generally constructive engagement with ONS – substantial concerns remain about data quality, methodological issues and communication.

Our judgement

We judge that while the MYEs continue to provide an important and valued source of population insight, work is needed to strengthen user confidence by enhancing transparency, communication and the clarity of quality information. Some users raised significant concerns with the quality of subnational estimates, particularly in local authority areas with high population churn. The data sources and methods used for measuring internal migration also require improvement. These limitations are well understood by ONS, which recognises them as priority areas for development and improvement. As ONS continues to develop its methods for estimating the mid-year population, further improvements to assurance, explanation and documentation would help reinforce trust in the statistics. Existing governance structures provide a strong foundation, and with clearer objectives, greater transparency and strengthened oversight, they can play an even more effective role in supporting high quality population estimates.

Based on the findings of this review, we have identified four requirements which ONS must meet by the time of its next publication in summer 2026 in order for the statistics to retain accredited official statistics status. These requirements are set out in full in the following section. In summary, ONS is required to:

Clearly and transparently explain the strengths and limitations of current MYE methods, and what it plans to do to address weaknesses.
Clearly explain pandemic impacts on the MYEs, justify claims of post‑2021 robustness, and actively engage users to ensure that its current guidance is helpful at highlighting any pandemic-related effects on the data.
Strengthen how it communicates uncertainty and limitations, particularly for non-technical users, and improve the navigation and accessibility of quality and methodology information.
Update and actively promote clearer guidance on which population estimates should be used for different purposes.

We have also identified several recommendations which ONS should address to further improve the statistics and enhance their Trustworthiness, Quality and Value. These recommendations include strengthening user confidence in ONS’s improvement plans and estimates, conducting deep-dive analyses to understand how estimates may have changed since 2021, resolving discrepancies with DfE school census data, enhancing quality assurance, undertaking a robust revisions analysis in summer 2026, and mitigating concerns about revisions and publication delays. We note that ONS is already developing and implementing plans to make improvements. In light of ONS’s focus on continuous improvement of the MYEs, our review findings should play a central role in shaping planned work.

Next steps

Confirmation of the continued accreditation of these statistics is conditional on ONS meeting Requirements 1, 2, 3 and 4 before or at the same time as its next planned publication of the MYEs in summer 2026. We expect a public update from ONS detailing how it has met these requirements by this point.

We will review and monitor ONS’s progress against our recommendations and expect ONS to report publicly to us on its progress in relation to these by the end of 2026. To add an additional layer of assurance, we recommend that the Population Statistics System Committee of the UK Statistics Authority play a role in overseeing ONS’s progress in response to the recommendations and report relevant updates publicly through its minutes every six months.