Discontinuity in the UK censuses on the definition of sex

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As reported in the Sunday Times (24 January 2021), the Chief Statistician Sir Ian Diamond has stated that the sex question in the forthcoming census in England and Wales will be framed in terms of legal sex, although it should be noted that this is still to be confirmed by the Office for National Statistics (ONS).

The statement by Mr Diamond does not mean that the sex question itself will change. The question simply asks ‘What is your sex? and has always allowed individuals to record whether they are male or female.

Rather, the statement refers to the accompanying guidance, which effectively frames the question by explaining how respondents should answer it. The issue then, is how sex is defined in the census.

Until last week, all three census authorities (England and Wales, Scotland, Northern Ireland) had proposed accompanying guidance that framed the sex question as one about self-declared gender identity, rather than sex registered at birth (i.e. biological sex), or ‘legal sex’, which for most people is their biological sex, but would also include around 5,000 people across the UK who have changed their legal sex in law via acquisition of a Gender Recognition Certificate

The move by ONS potentially introduces a significant departure from the Scottish Government’s position: in February 2020 the Cabinet Secretary for Economy, Fair Work and Culture confirmed that Scotland’s next census will ask a sex question framed in terms of self-declared gender identity.

As such, this creates impetus for Scotland’s census authority – the National Records of Scotland (NRS) – to shift to a legal sex question, or risk discontinuity in a core demographic variable between the jurisdictions. There is already significant discontinuity as a result of NRS choosing to postpone Scotland’s census to 2022, while ONS still intend to proceed in 2021.

Prior to 2011, no guidance for the sex question was provided. In the 2011 census, both ONS and NRS quietly introduced guidance stating that people could answer based on their own self-declared gender identity. In both cases, the guidance was introduced at the request of LGBT lobby groups, without wider consultation (see Figures 1 and 2 below).

Until last week, the ONS had indicated that they intended to proceed with similar guidance in the next census, although this remained under active consideration, in part as a result of recent interventions by the Office for Statistics Regulation (OSR) and the Chair of the UK Statistics Agency’s Methodological Assurance Review Panel, who requested assurances on data reliability. Expert data users have also repeatedly raised concerns about the about the impact on equalities monitoring and data reliability, particularly among smaller population groups (for example, by age and sex) (see here and here).

While not meeting concerns about the loss of data on biological sex, the prospective shift to legal sex nonetheless helps to alleviate some of the issues raised by quantitative data scientists, particularly around data reliability. The move would also set a welcome precedent for other data collection exercises, including crime recording, where as a result of lobbying, data on sex has already been replaced by that on gender identity.

As well as a sex question, in both England and Wales, and Scotland, the census will ask a new, separate voluntary question on gender identity for respondents who identify as transgender or non-binary. For ONS, having separate and conceptually distinct questions on sex and gender identity would mean a more balanced approach to different characteristics, and as a richer dataset.

What about Scotland?
The move by the ONS potentially introduces a significant departure from the Scottish Government position, which still supports framing the sex question in the Scottish census as one about self-declared gender identity, despite the new, separate question on trans status.

While advised by OSR that NRS should actively address the issues raised by expert data users, which include data reliability, there is no evidence to suggest this has happened. In response to concerns raised by Edinburgh University Professors Lindsay Paterson and Susan McVie, NRS stated that the guidance was settled, citing a letter to the Scottish Parliament’s Culture, Tourism, Europe and External Affairs Committee from the Cabinet Secretary for Economy, Fair Work and Culture:

I can confirm that, subject to the Census Order and Census Regulations being in force, the Registrar General will conduct a census that has a binary sex question with guidance that provides for a self-identification basis of response if required and I support this approach for Scotland’s Census 2021.

As a core demographic variable, this variation matters. It means that on either sides of the border, the census authorities would be defining sex in significantly different ways. It departs from the 2015 statement of agreement between the UK census authorities, aimed at securing comparable outputs across the UK.

‘Common definitions and classifications, typically based on international standards, should be agreed, used and published. [This includes a common population base.]

Common topics and questions should be agreed wherever possible, with the intention of making available consistent census outputs across the UK.’

It is also likely to exacerbate the significant discontinuity already introduced by the decision to delay Scotland’s census to 2022, while in England, Wales and Northern Ireland, the census remains on course to be held on 21 March 2021.

The potential move by ONS also puts England and Wales on a different track to Scotland more broadly, where recently published draft guidance by the Chief Statistician for Scotland advises that public authorities should cease collecting data on biological sex – apart from in some exceptional circumstances – and that in most cases this should be replaced with data on self-declared gender identity.

Figure 1. England and Wales census 2011: sex question guidance
Figure 2. Scotland census 2011: sex question guidance