ONS definitions of “Woman” in Statistical Classifications

Dyddiad y datganiad:
23 January 2026

FOI reference: FOI-2025-3308

You asked

I am submitting this request under the Freedom of Information Act 2000. 

I am requesting only information already held within ONS statistical classifications, coding standards, or metadata frameworks. 

No new analysis or interpretation is requested. 

Please limit your response solely to definitions recorded in classification systems, metadata documentation, census standards, or harmonised principles. 

I would be grateful for point-by-point confirmation of the following.

1. Statistical Classifications and Harmonised Standards
1a. Does ONS hold any definition or classification wording for "woman", "female", or "adult female" within its statistical standards or harmonised principles?
1b. If yes, please provide the recorded wording.

2. Census or Survey Metadata
2a. Do ONS census or survey metadata documents contain a definition of "woman", "female", or "adult female"?
2b. If yes, please provide the wording exactly as recorded.

3. Sex and Gender Coding Standards
3a. Do ONS coding frameworks include definitions that distinguish between biological sex and gender identity, specifically in relation to the term "woman"?
3b. If yes, please provide the wording exactly as held.

We said

Thank you for your request.  

While your questions relate to ONS statistical classifications, coding standards, or metadata frameworks, you might find it useful as context to understand how we use the terms "female" and "woman" in our outputs. 

Our data-collections generally use "female" rather than "woman" or "women", with the latter term used in relation to populations made up only of adult females. This is in line with guidance in our published "Service Manual" for ONS publications on language about Sex, gender and gender identity: 'If a population is made up of only adult females, it should be described as "women". If it includes children, use "females". If it is only children, use "girls".' (Equivalent guidance is provided for the use of "men" and "boys").  

1. Statistical Classifications and Harmonised Standards
1a. Does ONS hold any definition or classification wording for "woman", "female, or "adult female" within its statistical standards or harmonised principles?
1b. If yes, please provide the recorded wording.

There is currently no harmonised standard on the topic of sex. Full harmonised standards include definitions, survey questions, suggested presentations, and information for data users. The Government Statistical Services (GSS) Harmonisation team are currently working to harmonise measures of sex in statistical data collection across government1. While this work is taking place, sex harmonisation guidance2 is available setting out the way that sex has been measured in the UK censuses. The guidance does not provide definitions for the terms “woman”, “female”, or “adult female”, and instead provides links to the question text and associated respondent guidance used in the most recent censuses. This provides a reference for researchers seeking to use Census data or to compare with data collected using Census question designs.

A provisional, ‘under development’ standard for data on gender identity was published in July 2020, using research and testing undertaken for Census 2021 in England and Wales. This was archived in 2024, recognising the limitations to the data collected by this question. The GSS Harmonisation team has provided new guidance3 for producers of official statistics and researchers who are considering a gender identity question for their surveys while work to develop a new harmonised standard progresses. This guidance does not include any definitions for the terms “woman”, “female”, or “adult female”.

2. Census or Survey Metadata
2a. Do ONS census or survey metadata documents contain a definition of "woman", "female, or "adult female"?
2b. If yes, please provide the wording exactly as recorded.

Metadata for census questions is provided through several publications. None of these publications includes a definition of "woman", "female", or "adult female". 

The Census 2021 dictionary provides information about the questions asked, while each dataset contains a metadata page relating to the topic or topics covered in the dataset. For the sex question, the relevant links are: 

Both include the definition: 'This is the sex recorded by the person completing the census. The options were "Female" and "Male".' This is in line with the definitions used in previous censuses, which can be found via the UK Data Service website: Census definitions - UK Data Service 

For Census 2021, question guidance was provided online through the census website and by phone through our contact centre. The guidance can now be accessed through the Government Web Archive. The guidance for the sex question was changed on 9 March 2021; the two iterations of this guidance were:

For the gender identity question the relevant links are:

There is no specific definition of “woman”, “female” or “adult female” within any metadata associated with ONS social surveys definitions for sex or gender identity. The questionnaire for the Labour Force Survey (LFS) provides guidance for the sex question: “By sex we are referring to current sex.” The LFS is undergoing a transition to the Transformed Labour Force Survey (TLFS). The TLFS will aim to align with the new harmonised standard when available.

3. Sex and Gender Coding Standards
3a. Do ONS coding frameworks include definitions that distinguish between biological sex and gender identity, specifically in relation to the term "woman"?
3b. If yes, please provide the wording exactly as held.

The sex question as asked in the census and in our surveys does not use the term “woman” and does not have a free-text response option. For many surveys including the census, the response options are “Female” and “Male”, while some surveys include options of “Prefer not to say”, “Don’t know” or “Refused to answer”. There are therefore no coding frameworks for sex relating to the term “woman”.

The gender identity question asked in Census 2021 in England and Wales asked "Is the gender you identify with the same as your sex registered at birth?", with tick-box response options of "Yes" and "No". For those answering "No" there was a free-text box to write in their gender identity. The coding framework for write-in responses can be found in the dataset Census 2021: Quality of Census 2021 gender identity data. Responses of "No" to the initial question followed by "woman" were coded as "trans woman". How the respondent answered the sex question was not part of the coding for their response to the gender identity question. 

Gender identity is not asked in the regular ONS surveys, however it is asked on the Labour Force Survey in Northern Ireland. In that survey the question is the same as for Census 2021 in England and Wales, but with the tickbox response options of "Yes", "No" and "Prefer not to say". There is no free-text response option and therefore no coding frameworks relating to the term "woman".

Gwneud cais Rhyddid Gwybodaeth

Everything you need to know about Freedom of Information and how to go about making a request.