Table of contents
1. Quality information
Search-as-you-type for ethnic group
There was an increase in the number of people using one of the write-in response options to the ethnic group question. Each of these responses had a new search-as-you-type function in the 2021 online census questionnaire. The ethnic groups that offered this function were:
"Any other Asian background"
"Any other Black, Black British, Black Welsh or Caribbean background"
"Any other Mixed or Multiple background"
"Any other White background"
"Any other ethnic group"
We specifically designed the search-as-you-type function to make it easier for people to self-define when completing the census online. We believe that the new functionality encouraged individuals to identify their ethnic group this way. This may have partly contributed to the increases in numbers seen in these groups since 2011.
Combining ethnic groups
One way to analyse data is to compare values between groups. If you combine the many diverse ethnic groups from Census 2021 data into two broad groups, the insights and analysis may not be useful. You should use the five main ethnic groups at a minimum for your research, which are:
"Asian, Asian British or Asian Welsh"
"Black, Black British, Black Welsh, Caribbean or African"
"Mixed or Multiple ethnic groups"
"Other ethnic group"
Ordering of identity tick-boxes
The increase since the 2011 Census in people identifying as “British” and fall in people identifying as “English” may partly reflect true changes in self-perception. It is also likely to reflect that “British” replaced “English” as the first response option listed on the questionnaire in England. Read more about the change of this question in National identity question in the 2021 Census. Take care when interpreting results for these groups.
National identity is a self-identified assessment of people's own identity with respect to the country or countries with which they feel an affiliation. This assessment of identity is not dependent on legal nationality or ethnic group.
Search-as-you-type for Main Language: Other
The number of different main languages specified through people who answered "Other" to the question about main language is much lower than in the 2011 Census. This is likely to be because of the search-as-you-type function in the online questionnaire. It is believed the function reduced the number of write-in responses that did not match any language on a predefined index for coding. Read more about this coding process in Design for Census 2021.
There were changes in the top 10 languages spoken in England and Wales in Census 2021 from the 2011 Census. Some of these changes could, in part, have been because students were less likely to be at their term-time address because of the coronavirus (COVID-19) pandemic. Some of these students may have been overseas, returning to home countries during the coronavirus pandemic.
Our Maximising the quality of Census 2021 population estimates methodology provides information on student enumeration and processing.
Religion not answered
As religion was a voluntary question on the census, "missing values" on census responses were legitimate responses. We did not impute values to replace the missing value as with mandatory questions. This means that this topic includes a "not stated" category in outputs. Take care when analysing the data to avoid confusion between proportions of all people falling in a particular category and proportions of all people who stated a response falling in that category. It is recommended that percentages are calculated out of the total population, as opposed to those who have answered the question, to aid comparisons and interpretation.
An adjustment made to improve the estimation of students living at their term-time address will have slightly increased the proportion of "Not stated" and decreased proportions of other categories. Take care when interpreting data for those aged 18 to 22 years or, specifically, full-time students. Other than this, the effect of this adjustment should not materially affect analysis of these topics.
2011 religion classification
Take care when comparing the religion data from Census 2021 with the detailed religion classification from the 2011 Census. In 2011, an error in the processing of census data led to the number of usual residents in the "Religion not stated" category being overestimated by a total of 62,000 for three local authorities: Camden, Islington and Tower Hamlets.
We have published corrected figures for estimates based on the tick-box classification. However, it could not be corrected for the detailed religion classification because the processing and relationships with other output variables is so complex.
For this reason, only apply comparisons for these three local authorities to the tick-box classification and using the corrected figures set out in our Census products: Issues and corrections notice.
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3. Cite this methodology
Office for National Statistics (ONS), released 29 November 2022, ONS website, methodology, Ethnic group, national identity, language, and religion quality information for Census 2021
Contact details for this Methodology
Telephone: +44 1392 444972