Findings

2.1 Our findings are summarised into five key areas:

• ONS’s delivery of the 2021 England and Wales Census outputs
• quality assurance
• the impact of the pandemic
• user engagement
• UK coherence and future plans

ONS’s delivery of 2021 England and Wales Census outputs

Release plans and communication

2.2 The Census 2021 outputs for England and Wales were released in an orderly way, informed by input from users. Census 2021 outputs were available from the ONS census website, and ONS’s release plans and release calendar kept users informed about when to expect publications. ONS carried out a consultation seeking views on its proposals for the content design and release of Census 2021 outputs for England and Wales. ONS’s transparent publication of the responses meant that users could understand how their input shaped the final release plans.

2.3 ONS published the first results from Census 2021 on 28 June 2022. This was 12 months after the closure of the online questionnaire (25 June 2021), the primary data collection method for Census 2021. As noted by some users, this was a quicker turnaround for outputs when compared to 2011. The release provided rounded headline population estimates for local authorities in England and Wales by sex and five-year age group and the number of households with usual residents.

2.4 Users are kept up to date with ONS’s release plans via the website, but some users told us that they found it difficult to track what was being published and when and commented that ONS’s communication here was not clear.

2.5 The census outputs are grouped into three phases:

Phase 1 (from June 2022): ONS published the first results from the census, including datasets and methodology. Topic summaries by theme were published in autumn 2022, supplemented with information on the Census 2021 analysis programme.

Phase 2 (from March/April 2023): ONS published multivariate data for the usual resident population and short-term resident population data. It also created a new functionality that enabled users to create a custom dataset tool (also known as the flexible table builder) for the Census 2021 data.

Phase 3 (from summer 2023): ONS published statistics on national parks, approximated social grade data, alternative population bases, small populations, detailed migration data, flow data, microdata samples and additional geographies.

2.6 ONS initially aimed to publish first results in May 2022; however, this was pushed back to allow additional time to complete its local authority quality assurance exercise. ONS communicated its change in plans, including the reasons for it, in a published Census 2021 results update. Some users told us that they were disappointed with this delay and how it was communicated. As far as we are aware, the delay did not cause any detrimental impacts for ongoing use, and we support ONS’s decision to use the time for additional quality assurance work and the way it was communicated.

2.7 Any corrections or revisions to the census outputs were made in line with ONS’s revisions policy, with a notice included within the statistical bulletin. However, some users told us that it was not clear to them when estimates were revised, which has the potential to undermine trust in the outputs. We note that it was also difficult to assess the extent and scale of revisions or corrections made to Census 2021 outputs in the absence of a collective repository explaining any issues, such as this webpage available for the 2011 Census data, which continues to be updated.

Dissemination of the 2021 Census outputs for England and Wales

2.8 ONS’s range of 2021 outputs and online tools, in particular the census mapping tool and create a custom dataset tool, have allowed users to maximise the value of census data for their analyses and use. Users can navigate to the various outputs and tools via the ONS Census webpage, which was specifically designed for disseminating the 2021 Census data. Users were complimentary about the online tools, with some users finding the census mapping tool very helpful for visualisations and looking at statistics for geographical breakdowns. Many users also told us that ONS’s create a custom dataset tool supported their individual needs by allowing them to create specific tables for their own analyses.

2.9 ONS supported users’ understanding of the newly developed dissemination tools by hosting a range of webinars explaining how they can be used. These sessions were well attended; the “Introduction to Census 2021 flexible table builder” webinar had almost 500 attendees. Users reported an increased level of confidence in using the tools because of the webinars, and ONS received positive feedback about these sessions. Users told us that they found the webinar and the opportunity to directly engage with ONS on the create a custom dataset tool particularly helpful in developing their understanding of the tool itself.

2.10 ONS published the 2021 Census outputs in a way that considers the needs of its different users. The outputs, which include supporting statistical bulletins and data tables, cover a multitude of topics and varying breakdowns. Main statistics tables and bulletins are presented in a clear manner, and any accompanying text is well written, using plain language. Census outputs are available in English and Welsh, and supplementary videos are provided in British Sign Language.

2.11 ONS’s accessibility statement helps users understand how to make a request for a different format. For those users requiring more-detailed, granular-level breakdowns, the census data can also be accessed through Nomis. If required, users can also request additional data and statistics directly from ONS. Users told us that when they made ad hoc requests, ONS responded promptly and effectively to meet their needs.

2.12 User feedback on the ease of accessing the 2021 Census products was generally positive, despite some users sharing that they found the volume of publications available on the ONS website challenging to navigate. Some users told us that some familiarity or level of expertise with ONS’s outputs, including bulletins, data visualisation tools and quality information, was beneficial to fully navigate and use the suite of census outputs.

Quality information and quality assurance

Census response rates and use of methods

2.13 Census 2021 moved to a digital-first data collection approach, but paper-based questionnaires were still made available for respondents on request. Most responses were submitted online. ONS achieved a person response rate of 97% of the usual resident population of England and Wales, with over 88% population coverage in every local authority. This figure exceeded ONS’s target of 94% overall and 80% in local authorities and is a notable improvement from the 94% response rate observed for the 2011 Census.

2.14 ONS worked with NISRA and NRS to support consistency and met the United Nations’ international standards for censuses. ONS also engaged regularly with a range of Census Advisory Groups consisting of external experts, advising ONS on how to maximise the relevance, quality and usefulness of statistics produced from the 2021 Census. The group was also a consultative forum, providing technical advice and guidance on methodological developments.

2.15 The 2021 Census questions remained mostly unchanged from those used in the 2011 Census to maintain comparability over time and the methods used were an evolution of the those used in 2011. ONS used statistical techniques to adjust the 2021 Census counts for people that were missed by the census to reduce any potential bias. The methods approach was researched and developed in consultation with academics, statisticians, demographers and users of census data.

2.16 Where responses to the census were missing or incomplete, ONS used an imputation method to improve the quality of the data for users. Of the 26.3 million responses, 9% required one or more questions to be imputed. Most questions had an imputation rate of less than 3%, and the questions with the highest imputation rates were largely in employment-related variables. ONS also put measures in place to maximise the response rates of special population groups to ensure the data were representative of the population and published response rates by local authority and a range of person characteristics.

Quality assurance

2.17 ONS conducted rigorous quality assurance to understand and assure the reliability of the census results before publication. Guided by its quality assurance strategy, ONS used a range of quality assurance activities to ensure that the census data were robust and fit for purpose. This strategy included seeking feedback from stakeholder boards, groups and panels comprising a wide range of organisations. ONS sought comments on proposals from the Census Advisory Groups. These groups operated in a similar way to those held during the 2011 Census and were made up of a range of key stakeholders. Meetings were held regularly throughout the design, data collection and output development and publication. ONS also sought endorsement from the Methodological Assurance Review Panel, which provides external assurance on the methods which underpin ONS’s official statistics and research. To ensure transparency, the minutes and papers from these meetings are published.

2.18 ONS also carried out a Census Quality Survey (CQS) between June and August 2021 to assess the overall quality of the census. The CQS asks a sample of people the same questions as were asked on the census. Respondents are asked to think back to how they would have responded on Census Day. The CQS responses are then matched to each respondent’s census questionnaire. The CQS contained 24 questions and was answered by 8,724 households. The CQS sample was randomly selected from those who completed the census. ONS ensured that the sample was largely representative of the population based on a range of demographic characteristics.

2.19 ONS asked local authorities to review indicative census estimates for their areas. Many local authorities participated in this exercise, providing useful insight to ONS for their areas and supporting data quality. ONS did thorough internal reviews of all this evidence and used it to improve the overall data quality of the census, but this information was not made available externally for users.

2.20 Among the CQS questions, 58% had an agreement rate above 90%, and 68% had an agreement rate above 85%. These figures are comparable with those for the 2011 Census and with Northern Ireland’s 2021 Census. There were 2 household questions and 15 resident variables with agreement rates less than or equal to 90%. Nine out of the fifteen resident questions with lower agreement rates were connected to employment and economic activity. The disruptions and changes in working arrangements caused by the pandemic at the time of the census likely affected how people responded to employment questions. ONS did prepare guidance for those on furlough, but it is not known what fraction of people followed this guidance. In its analysis, ONS recognises that the census and CQS responses may not align and explores in more detail the reasons behind the differences.

Quality and methodology information

2.21 ONS has published a wide range of material on how the census data and statistics were collected and quality-assured. Information on a range of quality assurance plans and activities is available on the ONS website. For example, clear and detailed information on the CQS is available in a way that accounts for a wide range of technical abilities.

2.22 This quality assurance information is not always readily accessible. Information on plans for quality assurance of the census data and statistics, overviews and detailed information on quality assurance exercises were published over a relatively long period of time. Whilst the relevant information is available, it is not easy to navigate nor organised in a user-friendly way. Quality information is not linked from the data visualisation tools, and many related quality publications are not linked together. Users told us that quality information was not easily accessible, and it was often difficult to find relevant information, particularly for new users.

Using Census 2021 data affected by the pandemic

2.23 Overall, Census 2021 data for England and Wales are well regarded by most users as being of high quality. The high response rates and ONS’s extensive quality assurance process mean that most users have confidence in using ONS census estimates. The data from Census 2021 provide a snapshot of life in England and Wales at an unprecedented time. Given the unusual migration patterns at that time, the data collected during this time may well be unusual or different from what might have been expected, and this was particularly the case for topics such as employment and economic activity.

2.24 ONS included some explanation of the possible distortive effects of the pandemic in the statistical bulletins of the topic areas most likely impacted. For instance, the travel to work bulletin highlights that the national lockdown, associated guidance and furlough measures will have affected the travel to work topics. And the bulletin for the number of vacant and second homes states that ‘some people, for example, overseas students or those privately renting, may have moved back in with family members, leaving more unoccupied dwellings’.

2.25 ONS has not provided users with sufficient explanations of how to use the data within the context of the pandemic and the extent to which decisions should or should not be made based on these data. Users’ views here were mixed. Some users did not raise any concerns about the impact of the pandemic on either their use or the quality of the statistics, but others, particularly urban local authorities, raised significant concerns.

2.26 Given the quality assurance process that ONS has carried out, we are confident that the census data are of sufficient quality and captured an accurate snapshot of the population in England and Wales at that time. However, in the context of the pandemic, and considering that many people may not have been located where they would have normally been, some users have raised concerns about potential limitations of the data, which could impact how they can be used, or may mean more information is needed to support use. ONS should have provided more information to support use and in turn user confidence, particularly for local authorities.

2.27 Some users, particularly urban local authority users, felt ONS has not provided users with enough information about how pandemic impacts the use of census data in other population estimates, for example mid-year estimates. For example, due to the restrictions during the pandemic, people were not moving around in their usual ways. This unusual movement is particularly concerning for urban local authorities with typical high population churn. It is not clear how ONS has addressed this potentially distortive effect in its population statistics, such as the mid-year estimates, which take the census as the baseline measure from which future years are calculated.

2.28 Whilst we recognise that it is not possible to measure a world without a pandemic, it is vital that ONS publishes information that helps users to understand how the pandemic context affects the use of the data and the extent to which decisions should or should not be made based on these data. Providing this information would ensure that users are fully informed about the limitations of the census data when using them to project forwards.

2.29 In response to our direct engagement with ONS, it told us that is plans to publish a research paper on the impact of the pandemic, following on from Census 2021 in autumn 2025. It told users about this publication in its quarterly update on population and migration statistics: May 2025. We expect that this work will address the following requirement and look forward to reviewing in due course.

ONS's user engagement

2.30 ONS has carried out a wide range of user engagement activities to support as many users as possible in understanding and making use of the census statistics. These activities included directly engaging with users, seeking feedback through consultations and making a wide variety of resources and information publicly available on its website. Generally, users reported that ONS’s engagement was effective in communicating with a variety of users and taking their requirements into consideration. Many users noted that the outputs had successfully engaged users and potential users through clear communication and data visualisation tools, ensuring that data were publicly accessible for all.

2.31 ONS used a variety of methods to promote the Census 2021 consultations and outputs and engage with their users. It took a strategic approach to increasing awareness of the data, reaching a wide audience across England and Wales.

2.32 The census team was described as helpful and professional. Some users commented on how responsive the census team was when responding to queries and noted that the quality of communication was an improvement on previous censuses.

2.33 ONS used a variety of methods to engage with users about the Census 2021 outputs, including email updates, social media, census customer services, the school campaign “Let’s Count”, one-to-one stakeholder meetings, stakeholder groups, press releases, blogs and podcasts. The use of the outputs was supported by a range of webinars, for example, two webinars focused on supporting users with the create a custom dataset These webinars had over 800 attendees in total, and most attendees told ONS that they were more confident using the tool after attending.

2.34 The Census Commissioned Outputs team provides ad hoc tables and data in response to user requests. These tables contain combinations of data that are not available in standard publications, and ONS publishes these ad hoc tables for all to use under the Open Government Licence. Users valued this service and spoke highly of their interactions with ONS in this area.

2.35 ONS did not effectively engage with some users, particularly users who provided more challenging feedback for ONS. A small proportion of users told us that they did not know how this feedback was used and whether it was acted on, and if not, why. Comments of these nature commonly came from local authority users who had responded to ONS’s quality assurance exercise, but other users shared similar concerns.

2.36 ONS did not routinely feed back to the local authorities involved in ONS’s quality assurance process. Some local authorities, particularly those in urban areas, raised significant concerns about the indicative census estimates and committed resource to provide ONS with local evidence to support their views. Their main concern was that the population estimates were lower than they expected, particularly the figures for younger working-age adults. Some local authorities told us that ONS had not responded to the concerns they raised as part of this quality assurance exercise, so they do not know how their feedback was used or, if it was not used, why.

UK coherence and future plans

2021 UK census outputs

2.37 UK census outputs have not yet been published. ONS recently published a news item on its plans for UK census outputs, which was disseminated to users as part of the population statistics newsletter, with 35,000 recipients. It provides users with high-level plans for the outputs. Through its release calendar, ONS has indicated provisionally that the outputs will be released in either June or July.

2.38 ONS has not recently engaged with users to understand what users need from the UK census outputs. ONS told us that it had not received any requests for UK-level outputs. In our user engagement, four users told us that they would like to see UK-level outputs. One user said that they would like to see UK-level estimates because it would help inform UK-wide policy initiatives. Another told us that they are making their own decisions about combining data from across the UK, in the absence of this information from ONS or appropriate guidance on how to do this.

The future of population statistics

2.39 The future of population statistics across the UK is currently being considered by each of the UK governments. In 2014, the UK Government set out its ambition that ‘censuses after 2021 will be conducted using other sources of data and providing more timely statistical information’. In 2018, ONS committed to respond to this ambition with a recommendation to government with the ONS Future of Population and Migration Statistics programme. ONS conducted a public consultation in 2023 to understand the extent of population data user needs in England and Wales. The UK Statistics Authority (UKSA) Board will make a recommendation to the UK Government on the future of the census on advice from the National Statistician.

2.40 The outcome of the UKSA recommendation on the future of the census in England and Wales will significantly impact the broader UK statistical landscape. The census is the backbone of the UK statistical system, so any decisions around its future must be carefully considered, including the impacts on devolved governments and other statistical releases that heavily rely on census data. Strong collaboration between the three statistical offices continues to be crucial during this period of systemic uncertainty.

2.41 As demonstrated by ONS’s delivery of the 2021 Census (and in the delivery of other censuses across the UK), administrative data have a role in supporting and enhancing the collection of data held about our population. The future role of these data is yet to be determined. Whilst we recognise the challenges in deciding the future of census, we would like to see ONS publish the outcome of the recommendation, and its planned next steps, as soon as feasible.