11.
Strengths and limitations
Strengths
The census provides the most detailed picture possible of the entire population, with the same core questions asked to everybody across England and Wales.
The Office for Statistics Regulation has independently assessed the census estimates and checked compliance with the
Code of Practice for Statistics
. The UK Statistics Authority assigned
National Statistics
designation to Census 2021 outputs, providing assurance that these statistics are of the highest quality and value to users.
We undertook a rigorous and comprehensive quality assurance process, including comparing against the widest range of alternative and complementary data sources ever. In addition, for the first time, we invited local authorities to review provisional census estimates, drawing upon their local expertise, in parallel to our own quality assurance checks. Detailed information is provided in our
Maximising the quality of Census 2021 population estimates report
.
Census estimates are important for understanding the accuracy of other population estimates. For example,
mid-year population estimates (MYEs)
are based on the most recent census and adjusted for live births, deaths and migration, but the potential for error in MYEs increases over time between censuses. We are also developing
admin-based population estimates (ABPEs)
, which use administrative data sources rather than being based on census estimates. Reports comparing the Census 2021 population estimates with the latest MYEs and ABPEs, including explanations for any differences, are planned for publication later this year.
Our very high response rate and extensive online collection has ensured that we have collected extremely high-quality data about the population and its characteristics on Census Day. It was particularly important to understand how the coronavirus (COVID-19) pandemic affected, and continues to affect, our population in a variety of ways (for example, health impacts, working from home). Census data and our ongoing transformation of our social statistics system will help us to both understand and to measure population change more effectively than ever before.
Limitations and mitigations
The first results from Census 2021 provide early rounded population and household estimates for England and Wales; figures may not add exactly because of this rounding. Unrounded figures will be released in autumn 2022. Figures may differ slightly in future releases because of the impact of removing rounding and applying further statistical processes. Unrounded historical census data are used for all comparisons with previous censuses.
Census statistics are estimates rather than counts, and therefore have measures of uncertainty associated with them. We take numerous steps to minimise possible sources of error, as described in our
Quality and Methodology Information (QMI) report
.
The coronavirus (COVID-19) pandemic may have affected some people's choice of usual residence on Census Day, for example, students and in some urban areas. These changes might have been temporary for some and more long-lasting for others. We discuss what this means for the data in our
QMI report
.
No census is perfect - some people are inevitably missed or counted twice. Our Census Coverage Survey (CCS) enables us to estimate how many people have been missed or double-counted. We also have processes that check for and resolve multiple responses, allowing us to adjust the census counts accordingly. More information is provided in our
Maximising the quality of Census 2021 population estimates report
.
As with all self-completion questionnaires, some forms will have contained incorrect, incomplete, or missing information about a person or household. We used editing and imputation strategies to correct inconsistencies and missing information. Further information will be provided in a more detailed report later this year.
National Statistics status for Census 2021
These National Statistics have been independently assessed by the UK Statistics Authority. They have been produced by following the standards set out in the
Code of Practice for Statistics
and the
Statistics and Registration Service Act 2007
.
This means that they:
meet identified user needs
are well explained and easily accessible
are produced based on appropriate data and methods
are managed impartially and objectively in the public interest
Date of most recent full assessment: June 2022
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