Sex is a key demographic variable and collecting high quality, robust data on sex is critical to effective policymaking across a wide range of fields, from health and justice to education and the economy. It enables policymakers to measure and address disparities between women and men, and girls and boys. The government has a strong interest in promoting high- quality data on sex, both in its role as a funder of research and as a producer and user of statistics.

Accurate record keeping is also vital for operational purposes, for safeguarding and, within the healthcare system, for patient safety and care.

Stakeholders have told us that they recognise the importance of collecting data on sex. Confusion regarding the legal position has posed a barrier to collecting data on sex for some organisations. This report includes specialist legal advice which is presented in appendix 1.

Both people’s material circumstances and their identities are important to their lives. We know that sex affects many dimensions of people’s lives, and we have much to learn about the ways in which having a transgender identity matters too. Rather than removing data on sex, government and other data owners should collect data on both sex and transgender identities, in order to develop a better understanding of the influence of both factors and the intersection between them.

Collecting data on sex does not reduce people to biological categories, neither does it imply that people should conform with the stereotypes associated with those categories, nor does it deny the existence or experience of people with diverse gender identities . Indeed, people with diverse gender identities are being let down by data collection practices which conflate sex and gender identity, making it impossible to track the outcomes of distinct groups.

Respondents may understandably question why they are being asked for certain information. It is vital that everyone participating in research or providing data for administrative purposes is treated with respect and is informed about the reasons for data collection and reassured about the way their data will be processed and used. Some respondents may be reluctant to provide data on sex while others are reluctant to provide data on gender identity. In both cases, the purposes of the data collection, including potential benefits to the individual and society, should be explained.

We have documented arguments against treating sex as a binary variable. These include arguments which instrumentalise the lives of people with Differences of Sex development (DSD) and propagate myths such as the claim that these rare conditions are ‘as common as red hair’ or that people with DSD do not have a sex. This has resulted in inappropriate and intrusive questions being asked about DSD.

Censuses and surveys internationally are increasingly seeking to capture information about the trans and/ or gender-diverse population. They have approached these questions in different ways and with varying results. It is critical to establish a clear target for any question on gender identity. Stakeholders have expressed a need for clear guidance on data collection in this area. Questions which conflate sex and gender identity have become common, but do not effectively identify the gender diverse population.

In order to test hypotheses regarding the importance of sex and gender identity in any context, distinct variables are required in order to avoid the multicollinearity which arises when a sex/gender hybrid variable is used in the same analysis as a sex variable. Multicollinearity refers to a high degree of correlation between explanatory variables in a statistical analysis. Sex/gender hybrid questions are not useful in disentangling the effects of sex and gender identity because in practice these questions elicit information on sex from most respondents.

In some cases, the conflation of sex and gender identity has been embedded in shared IT systems, posing a barrier to organisations wishing to collect data on sex. For example, a data management system used by rape crisis centres in Scotland uses the following ‘gender’ fields for both victims and alleged perpetrators: Male/ Female/Intersex/Gender queer/Other.

In the absence of a single source of authoritative guidance on data collection on sex and gender, various organisations have developed their own guidance. We reviewed guidance produced by national governments, non-departmental public bodies including regulators, prominent organisations engaged in market research, and a small number of charities working on issues relating to sex and gender. We found that guidance produced by many of these organisations lacked conceptual clarity, often eliding data on sex with data on self-declared gender identity.

There are well-established principles of question design which should be applied to any topic (we outline these in chapter 2). These principles have sometimes been overlooked in the field of sex and gender due to the politicisation of these questions. It is important to remember that the purpose of survey data collection is to gather data about populations rather than to provide an opportunity for each individual to express the full complexity and richness of their identity.

We recognise the high standards which the Office for National Statistics (ONS) typically upholds. However, we have seen evidence of a partisan climate on certain issues, including gender, within the organisation (see chapter 5). Political impartiality (which must be understood broadly, not simply in terms of party politics) is a principle of the Nolan Principles of Public Life. In addition, the UK Statistics Authority Code of Practice states that ‘People in organisations that release statistics should be truthful, impartial and independent, and meet consistent standards of behaviour that reflect the wider public good’.

Review of data collection practices

As part of the review, we examined over 800 administrative and research datasets, surveys, and data collection policies. Our analysis revealed that:

The meaning of sex is no longer stable in administrative or major survey data. This instability is evident across key policy areas including health and justice. This has led to a widespread loss of data on sex.
In some cases, the loss of data on sex poses risks to individuals. This is particularly apparent within health and social care. These risks are especially high in the case of minors.
How sex is defined is rarely made apparent in published outputs, including accredited official statistics. Some publications provide this information in accompanying documentation.
Some publications present binary data on sex but are underpinned by survey instruments that included additional response options, such as ‘other’.

Source: https://www.gov.uk/government/publications/independent-review-of-data-statistics-and-research-on-sex-and-gender/review-of-data-statistics-and-research-on-sex-and-gender-executive-summary