1. Quality information

Reliability of estimates

Census 2021 was the first census to provide estimates of gender identity, and so while there are no previous directly comparable estimates available, the estimates are considered broadly in line with other data on gender identity. All census estimates contain a degree of statistical uncertainty as described in the Section 6 of our Quality and methodology information (QMI) for Census 2021. This uncertainty will be proportionately higher for relatively small population groups such as those who report a gender identity different to their sex at birth. This relative uncertainty will increase if the population group is further broken down by geographic area or other characteristics.

Not answered

As sexual orientation and gender identity were voluntary questions in the census, missing values on census responses were legitimate responses. So, (unlike with mandatory questions) we did not impute values to replace those missing on received responses. This means that these questions include a "not answered" category in standard outputs. Any write-in responses that did not relate to the question were coded as if the question had not been answered. Take care to not confuse between proportions of all people aged 16 years and over falling in a particular category and proportions of all people aged 16 years and over who answered the question falling in that category.

Data collection and coding

As with all census questions, the questions on sexual orientation and gender identity were tested thoroughly as described in our Sexual orientation question development for Census 2021 and Sex and gender identity question development for Census 2021. The final questions collected information on these topics using a combination of tickboxes.

Answers for these questions did not always correspond to well-defined concepts and write-in answers have been coded, both automatically and manually, to categories shown in published tables. While overall estimates for both these topics are consistent with other available sources it is possible that the comparability of individuals’ responses was affected by different interpretations of the questions and that proxy responses for these sensitive topics may be less accurate than for other topics. A proxy response is where someone has answered the census questions on behalf of someone else.

Student adjustment for sexual orientation and gender identity

An adjustment made to improve the estimation of students living at their term-time address will have slightly increased the proportion of “Not answered” and decreased proportions of other categories. Take care when interpreting data for 18- to 22-year-olds or, specifically, full-time students. Other than this, the effect of this adjustment should not materially affect analysis of these topics.

Age and geographical distributions

Census data on sexual orientation and gender identity show age and geographical patterns which may affect relationships between these topics and topics such as education, employment, health and housing. In particular, people who report a sexual orientation other than ‘straight/heterosexual’ and people who report a gender identity different from sex registered at birth are more likely than average to be younger and to live in urban areas. You should be aware of these factors when drawing conclusions from the census estimates for these topics.

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3. Cite this methodology

Office for National Statistics (ONS), released 6 January 2023, ONS website, methodology, Sexual orientation and gender identity quality information for Census 2021.

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Contact details for this Methodology

Census customer services
Telephone: +44 1392 444972