Thread by @MForstater

Old Census forms....

One of the ideas that is getting bandied around is that "sex" has always been self identified on the census.

This is codswallop...

And as the ONS say it is important to maintain comparability over time

census.ukdataservice.ac.uk/use-data/censu…

One of the things in census design is also making sure that relationships between the questions are consistent

- with the modern census they use computer power to weed out errors like people who listed as under 16 and in full time work , or women giving birth over 65 etc...

The census asks about relationships between people in the household

In 1971 they put this as the "Head" of the household (i.e. the husband/father if their was one) and the wife.

The 1971 census also asked some specific questions of women - which clearly relate to biology

(not that there was a distinction between legal sex and biological sex in 1971)

By 1981 the marriage question was phrased in less sexist terms.

You answer how is person 2 related to person 1.

Legally only a woman could be married to a man then

So a "self-identified" gender/sex would yield a computer-says-no response when it came to data crunching

In 2005 same sex civil partnerships were brought in, so this was included as an option in the 2011 census (the last census)

A same sex husband or wife or opposite sex civil partner would have yielded a computer says no response here

So this means, in effect in 2011 the "sex" Q was legal sex (i.e. taking into account GRA 2004 for a tiny number) - since this is the only answer that would maintain consistency w the answers on marriage.

Self identified sex would have been read as an error for a married couple

As the ONS said at the time if a person ticked both "male" and "female" (to indicate non-binary) a single response would be created

It is likely one of the corroborating pieces of data and rules used to create that single response would be marriage

whatdotheyknow.com/request/census…

Nevertheless the ONS said in its online guidance to answer according to "self identified sex"

Presumably they thought this was a fudge they could get away with because (1) not much attention was being paid and ...

... (2) given that same sex marriage was not yet legal it would not be possible for a transsexual person to be living in 'stealth' as the opposite sex and also be married IRL

In 2013 same sex marriage was brought in, & in 2019 civil partnership was opened up to opposite-sex couples.

So now there is no computer-says-no error detection between marriage and the the sex question.

But this doesn't mean that the definition of sex has changed

To maintain comparability with 2011 it should be legal sex.

To maintain comparability with every census before that it should be biological sex