Recent months have witnessed an acceleration in attempts to erase trans people from data collection activities in the UK, the last-minute change to guidance for the sex question in the English and Welsh census is only the latest example of data vandalism.
On 12 February 2021 the Office for National Statistics (ONS) issued new guidance on how to answer the question ‘What is your sex?’ in the 2021 English and Welsh census. The new guidance explained: ‘If you are considering how to answer, use the sex recorded on one of your legal documents such as a birth certificate, gender recognition certificate, or passport’.
Alongside its announcement of the revised guidance, the ONS also published a 32-page account of the methodology and evidence used to inform its decision. In the document, the ONS describes how it considered five concepts of sex that the census could collect data on:
- Sex as registered at birth
- Sex as recorded on birth certificate
- Sex as recorded on legal/official documents
- Sex as living/presenting
- Sex as self-identified
For each concept, the ONS then evaluated whether this would (i) maximise census responses and (ii) ensure any perceived invasion of privacy is justified.
The ONS arrive at the conclusion that guidance aligned to ‘Sex as recorded on legal/official documents’ was the best option for the 2021 census, although the concept ‘Sex as living/presenting’ actually had a less negative impact on the census (the report fails to explain why ‘Sex as recorded on legal/official documents’ was chosen rather than ‘Sex as living/presenting’).
Jump forward to March 2021 and, following a court case brought against the ONS by campaign group Fair Play for Women, an interim ruling forced the ONS to remove the words ‘such as’ and ‘or passport’ from the guidance so that respondents were advised to answer according to the sex recorded on their birth or gender recognition certificate. The ONS chose not to defend their position and the interim ruling was therefore maintained.
Red, amber and green
In practice, the court case therefore changes the concept asked about in the English and Welsh census from ‘Sex recorded on legal/official documents’ to ‘Sex recorded on birth certificate’.

Helpfully, the ONS had already evaluated differences in collecting data on these two concepts in their 32-page account of methodology and evidence, using a red, amber and green (RAG) traffic light system.
In terms of maximising census responses, ‘Sex as recorded on legal/official documents was Green (no evidence of negative impact on overall response or sex question response across all groups either at the individual level or at a societal level) whereas as ‘Sex as recorded on birth certificate’ was Amber (evidence of negative impact on overall response or sex question response for subsets of society either at the individual level or at a societal level).

In terms of ensuring any perceived invasion of privacy is justified, ‘Sex as recorded on legal/official documents’ was Amber (data need insufficient to justify collection of data, OR trans respondents would be forced to reveal their gender history) whereas as ‘Sex as recorded on birth certificate’ was Red (data need insufficient to justify collection of data, AND trans respondents would be forced to reveal their gender history).

Using the traffic light system designed by ONS, we see how this month’s court case has negatively impacted the collection of data about sex in the census on both counts (moving from Green to Amber and Amber to Red, respectively).
Policing how trans people answer the census
The case brought to the High Court was not intended to alter how cis respondents (people whose gender identity matches their sex assigned at birth, estimated to be around 99% of the population) answer the sex question, as highlighted in the table below. Rather, the case’s purpose was to police how trans respondents without a gender recognition certificate (GRC) answer the census.

A wake-up call for researchers
This debacle must serve as a wake-up call for researchers engaged in the collection, analysis and use of quantitative data about identity characteristics. As well as posing wider questions as to the relationship between evidence-based decision making undertaken by statistical and research organisations and crowdfunded legal challenges, which can quickly undo months if not years of detailed research.
Aware of these issues, scientific experts in quantitative data, surveys and/or large datasets have written an open letter stating that the self-reporting of lived sex in the census poses no threat to the collection of high-quality data. This follows a previous letter in September 2019 from researchers, academics, practitioners and data users to the Scottish Parliament to state that trans people should continue to answer the sex question in the census in line with how they live.
The data vandalism instigated by this month’s court case is not necessarily about how changing guidance necessarily disrupts the count but the trust and confidence in organisations like the ONS to capture data about gender, sex and sexuality that is inclusive and reflective of people’s day-to-day lives.
Nobody checks how anyone answers the census and the ONS remain clear that census guidance is only intended for those who need help in answering a question. This month’s court ruling and a change to the sex guidance will therefore not alter how trans people, who choose to engage with census, answer the sex question. However, the optics of this decision and the likelihood of further campaigns intent on policing how trans people participate in data collection activities is likely to have a negative impact on efforts to capture vital data about individuals’ gender, sex and sexuality.