About the GSS Harmonisation Team
The Government Statistical Service (GSS) Harmonisation team is based in the National Statistician’s Office, within the Office for National Statistics (ONS). The team:
- is responsible for creating and embedding the UK Government’s ‘harmonised standards’ for all topics
- supports the harmonisation of data across the UK
Our work involves providing bespoke advice and harmonised standards and guidance about how data on different topic areas should be collected and presented to help support statistical producers. The Code of Practice for Statistics recommends that organisations producing official statistics should seek to design new statistics in ways that achieve UK comparability and improve consistency and coherence with related statistics, but does not mandate the use of harmonised standards. Others may also choose to use these standards where they help the consistency, comparability and coherence of data and statistics.
Background to this review
In December 2024, the GSS Harmonisation team announced a new phase of work towards developing harmonised standards for sex and gender identity data collection.
Our way of working is in line with the Government Design Principles, which reinforce the importance of building an understanding of user needs, and designing iteratively based on evidence. Both agile methodology and the Respondent Centred Design Framework emphasise the importance of gathering user needs early in project delivery, and using these needs to inform all subsequent work you undertake. The methodology we use for question design is all about ensuring evidence-based respondent-first research, in a multi-modal, research context. By developing harmonised standards iteratively based on the needs of our users and the feedback we gather from respondents, we can ensure the final harmonised standards are effective, evidence-based, and fit for purpose. Our job is to understand what statistical producers and data users need from their collection. We can then match this to a way of collecting that data which respondents will understand and be willing and able to answer.
This report presents the latest findings from our work to review user needs for harmonised standards on sex and gender. Our research with respondents to develop standards which address these user needs has been published separately for sex. We will also publish our research on the topic of gender identity as that workstream progresses.
We published a first report on our early research findings on sex and gender identity in May 2026. In that report we set out our findings that inconsistencies in the way sex and gender identity are defined and collected across UK surveys can pose risks to data quality and the coherence of statistics. Statistical producers across the GSS told us that they needed support and guidance to assist the collection of high quality data on sex and gender identity. In particular, they wanted standards that addressed:
- terminology and concepts
- question placement and ordering, both within a survey and between questions
- the applicability of proxy responses for sex and gender identity data collection
- data handling and presentation after collection
These GSS users emphasised a heightened requirement for standardised questions on sex, which would enable compliance with legislation and official frameworks. Consequently, we accelerated testing for a harmonised standard which supports data collection for:
- Biological sex (sex at birth) aligned with the definition for the purposes of the Equality Act, 2010,
and - Certificated sex (sex at birth or as modified by a Gender Recognition Certificate) aligned with the legal recognition provided by the Gender Recognition Act, 2004
Since this publication, further work has been completed to better understand user needs for harmonised standards on sex and gender identity, and to determine how to address these going forward. As our workplan progresses, we will continue to develop our understanding of user needs, and question and data issues.
This report presents our findings to date. We are publishing this now to provide transparency and to gather feedback on the user needs collected so far.
User needs for harmonised standards
In November and December 2025, we held a series of online roundtable discussions with data collectors and statistics producers recruited from across the GSS. In total, 54 GSS colleagues from 31 government departments, devolved governments, and public bodies took part in these events. A further nine colleagues took part in online roundtable discussions in March 2026, focusing on the data user needs of cross-government policy professionals.
We sought to understand the needs of cross-government statistical producers and data users who collect or use data on sex and gender identity topics, or who intend to. This included exploring:
- potential inconsistencies and differences in user needs
- challenges when collecting, producing and using statistics on sex and gender identity topics
- whether producers and data users had additional needs for data collection on sex and gender identity topics which were not fulfilled by existing data collection practices
Our primary focus in this phase of work was to engage with user needs from within the Government Statistical Service (GSS), in line with the Harmonisation team’s primary goal to improve the consistency, comparability and coherence of data and statistics across Government. We expect to carry out further roundtables with users later in 2026, this time with data users beyond government (for example those in academia, or the third sector).
We also intend to carry out further research into user and respondent needs for harmonised standards on gender identity, gender reassignment, trans status and trans history. These are more recent topics in official statistics. This means there is a need for further research to clearly articulate the needs of data producers, data analysts, and respondents, to ensure that data collection designs are clear, accessible, and fit for purpose.
Identified user needs
User need 1: Harmonised standards for sex and gender identity which encourage consistency across collection sources and over time, aiding data comparability
Users who collect or use statistical data on sex and gender identity need to be able to compare data across different data sources, including calibration with population measures from the UK’s censuses. In some cases, their user needs are established by the need for alignment with data collection in another Department, but even where a statistical instrument is designed to meet local user needs for data, there is a strong desire for consistency across Departments and over time.
Where questions have changed over time, users raised concerns about how this may affect comparability, and the desire to ensure future collection is reliable and consistent. They also identified a challenge in that concepts for sex and gender identity may continue to develop over time. This means there is a need for harmonised standards which would be robust and flexible enough to handle this.
User need 2: Harmonised standards for sex and gender identity which use clear and distinct terminology and concepts, and are legally compliant
Users raised concerns that the collection of accurate sex and gender identity data is difficult due to widespread conflation of terms. Both statistical producers and data users need target data collection concepts which are clear and distinct in order to be definitive about the way data are labelled and used. This includes the need for data on people with diverse identities, including trans identities and non-binary identities.
Users were concerned that respondents were not necessarily clear on the differences between different concepts of sex, gender, and gender identity. They need to be clear what data a given question is collecting and ensure respondents know what they are being asked to provide.
Users expressed the general need to ensure data collection was aligned to the UK’s legislative framework, noting that the legal definition for sex and the applicable legislation may differ in different contexts. Users expressed concern and confusion over which concept to use and noted the need for clarity on legal compliance, terminology and concepts, as well as the need for guidance on question wording support. Users have implemented the 2021 Census for England and Wales data collection question for sex, which aligned to the 2004 Gender Recognition Act (sex recorded at birth or Gender Recognition Certificate).
Users who need to collect data to fulfil their Public Sector Equalities Duty expressed the need for their data collection to be compliant with the Equality Act and to collect data based on sex at birth in line with the 2025 Supreme Court ruling.
User need 3: Sex and gender identity questions which meet respondent needs for acceptability, comprehension, inclusivity and information disclosure, and promote trust
Users who collect or use data on sex, gender identity, or both, need to ensure the questions they ask will produce valid data. This means ensuring that questions relating to sex and gender identity are understood by respondents, and also that respondents find the questions acceptable. This is important to help with the willingness of respondents to provide data through the survey instrument. Users raised this as a particular challenge for question development if the target question concept does not align with the way an individual wants to represent their own identity, since smaller groups may be under-represented in the data if they have a higher probability of questionnaire drop-out.
Users also raised concerns about questions which force disclosure of sensitive topics, such as gender identity or trans status. The need for data collectors to build trust with respondents by demonstrating inclusive question development practices was considered important in showing how diverse groups of respondents were reflected in research and policy development.
User need 4: Harmonised standards which include guidance for statistical producers on how to implement and administer sex and gender identity questions in data collection, including in administrative data
Users who collect sex and gender identity data need guidance to help them use and update questions on sex and gender identity in their collection instruments. This includes guidance on:
- question placement
- question ordering
- the applicability of proxy responses in surveys
Users identified particular challenges with multi-modal data collection, where data may be collected through various different mechanisms such as face-to-face and online interviewing. Question testing will also be required to meet the language requirements of the UK to ensure questions in Welsh and English produce comparable data.
Another complex data collection circumstance is where researchers rely on the secondary use of data sourced from administrative collections. In some contexts, this may mean a third party has made a judgement call about the person they are recording data for.
User need 5: Harmonised standards which include guidance for data collectors on data handling and presentation
Users who collect sex and gender identity data also need guidance to help them with end-to-end handling for the data, including data aggregation for small populations, data validation, and disclosure controls for published outputs. Privacy concerns and compliance with GDPR in data collection and processing were raised as challenges. Handling free text data was also identified as an area requiring further support, as users raised the challenge of balancing a respondent’s desire to self-define their gender with the statistical need to categorise outputs.
Users also raised the challenges associated with analysing merged data, where information may have been combined from across multiple low level data collections using variations of question wording and categories.
User need 6: Transparency and practical updates on the harmonised standard development which are regularly communicated
Users who are looking to implement or update their questions on sex and gender identity are looking for question development to be carried out using best practice methods. However, they highlighted their need to balance development timelines with their urgent need for data collection which is legally compliant and meets their own stakeholders’ data needs.
While some users have sought to avoid making a substantive change until clarity could be provided by the GSS on a harmonised approach, other users have initiated their own question testing research processes. There is, therefore, a strong need for the GSS to accelerate its development, and to provide frequent updates to users on the research evidence. This is necessary so that users can plan ahead for the implementation of an evidence-based harmonised standard. Users who have engaged in their own interim research on user needs and question testing also need regular updates on GSS work, in order to share learning.
Conclusion
Statistical producers and data users who work with sex and gender identity data within the GSS have multiple needs. They can find current data collection tools challenging to work with because of a lack of clear and distinct terminology and concepts. They are also concerned that the implementation of new standardised questions should encourage consistency across collection sources and over time, while meeting respondent needs for acceptability, comprehension, inclusivity and information disclosure.
To meet user needs, future harmonised standards should provide guidance both on how to implement and administer sex and gender identity questions in data collection, and on data handling and presentation.
Users need regular communication on the progress towards harmonised standards, providing transparency and practical updates on development.
We will continue to investigate needs and issues with respondents and data users outside the GSS, and will include these in a future update.
What happens next
The GSS Harmonisation team recognise how important it is for statistical producers to be able to rely on evidence-based harmonised standards for data collection on sex and gender identity. We started respondent testing for sex data collection questions in Spring 2026, reflecting the urgent user need for statistical guidance shared with us by official statistics producers.
We will carry out further research and engagement in the coming months, exploring user needs for data on sex and gender identity beyond government (for example, within academia and the third sector). We are also planning further research during 2026 to deepen our understanding of user needs for data collection on gender identity, gender reassignment, trans status and trans history. We will start respondent testing for gender identity questions following this work.
We also expect to carry out further qualitative research and engagement with populations who have variations in sex characteristics (VSC, sometimes referred to as intersex, or differences of sex development) during this time.
Contact us
If you would like to stay up to date with information about the development of new sex and gender identity harmonised standards, or would like to contribute to our future research on data user and respondent needs described in this report, please contact Outreach.Engagement.Comms@ons.gov.uk.