Compliance review: Mid-year population estimates for Wales
Overview
At the time of this report, the mid-year estimates (MYE) of the population produced by Welsh Government are published as accredited official statistics.
The latest release provides estimates of the population of Wales as of 30 June 2025. It includes breakdowns by local authority and by age, and components of population change, namely births, deaths, and net migration. The estimates are used to provide demographic trends in Wales as well as support decisions for resource and funding allocations, public services, planning and policy. This report shares our views on how the MYE for Wales meet the standards set out in the Code of Practice for Statistics (the Code).
Why we did this review
In May 2026 we published the findings of our review of the mid-year population estimates for England and Wales, produced by the Office for National Statistics (ONS). We are now in the process of carrying out similar reviews of mid-year population estimates for Scotland, published by National Records of Scotland (NRS), and mid-year population estimates for Northern Ireland, produced by the Northern Ireland Statistics and Research Agency (NISRA).
ONS is responsible for the production of the estimates in England and Wales and provides data to the Welsh Government for Wales-specific estimates. To ensure UK-wide coverage in our regulatory work, we carried out a light-touch review of the Welsh Government’s mid-year population estimates, focusing on their presentation and communication of uncertainty. These estimates were last reviewed against the Code by OSR in 2015.
Findings
Welsh Government works closely with ONS to produce the MYE for Wales. Welsh Government is part of ONS’s continuous improvement steering group for population estimates, providing input on ONS developments and representing the needs of Welsh users.
Welsh Government has pre-release access to provisional data from ONS for quality assurance purposes. However, there is no formal timetable with expectations for ONS to provide Welsh Government with the data and supporting material required for the Welsh Government release.
Clear definitions and explanations of key concepts are provided throughout the bulletin. Charts are accompanied by explanatory descriptions and source information, helping users understand and interpret the statistics.
Revisions to the latest estimates are clearly communicated throughout the bulletin, helping users understand what has changed, and interpret the estimates appropriately.
Welsh Government keeps users informed about population estimates and plans through various channels, including its Chief Statistician’s update blog and demography newsletters. Although the latest demography newsletter signposts users to relevant ONS material on the quality and improvement of population estimates, this was not signposted in the main bulletin. The newsletter was published two months after the Welsh Government release, meaning users may have missed important information when first accessing the estimates.
Welsh Government provides a high-level explanation of how uncertainty in the estimates increases over time and signposts users to ONS’s local authority uncertainty information and ONS’s Population estimates for England and Wales quality and methods guide. Unlike ONS, the MYE for Wales bulletin does not provide advice to users on appropriate use of the estimates and there is no quantitative uncertainty measure specifically for Wales.
Our judgement
We conclude that the MYE for Wales produced by Welsh Government continue to meet the standards set out in the Code of Practice for Statistics and should retain their accredited official statistics status. Based on the findings of this review, we have identified four recommendations that Welsh Government should address to further enhance the statistics’ Trustworthiness, Quality and Value.
Recommendation 1:
To support the ongoing timely production and quality assurance of the Welsh mid-year population estimates, Welsh Government should work with ONS to formalise and agree a consistent timetable for pre-release access.
Recommendation 2:
To enhance user understanding of the quality and limitations of the estimates, Welsh Government should signpost relevant quality information directly and prominently within the main bulletin. For the 2025 release, Welsh Government should add links to ONS’s quality information relevant to local authorities and describing the effect of the pandemic.
Recommendation 3:
To improve users’ understanding of uncertainty at the national level, Welsh Government should explore with ONS the feasibility of producing uncertainty measures at a Wales level and communicate the outcome of this work to users.
Recommendation 4:
To support appropriate interpretation of the statistics, Welsh Government should explain clearly in its bulletin what the MYE can and cannot be used for, including the limitations and uncertainty that users should consider when interpreting changes over time.
Next steps
We expect Welsh Government to implement our recommendations in time for its next MYE release in summer 2027 and to provide OSR with a public update on its progress by the next release.