Census data for those who entered a non-binary sex

The request was successful.

Dear Office for National Statistics,

In the run up to the 2011 census, transgender and transsexual people contacting Census Customer Services were advised to answer question 2, 'What is your sex?' with the option that most closely matched their self identity, rather than their legal status.

Several transgender individuals who genuinely do not identify as female or male were also advised that if they were to tick both of the options provided, they would not be penalised for failing to answer a required question.

In another Freedom of Information request response, your Office has explained that when indicated sex or marital status does not correspond with expected or 'legally recognised' structures, this may be 'resolved using a probabilistic statistical system'. Reference:


Could you please explain:

1a) How is the 'sex' question used in census statistics? What is an answer of 'male' or 'female' taken to mean?

1b) How the ONS compensates for the inaccuracies/ambiguity introduced by conflating the separate concepts of sex, social gender, legal gender and gender identity into one binary question?

2a) Does the census system accept answers for this question other than responses of only 'male' or 'female'?

2b) Will the figures be made available for the number of people who answered census question 2 to indicate they are:

i) Both male and female
ii) Neither male nor female
iii) Some other sex/gender, indicated by adding an additional box or writing an answer in the space around the question
iv) Abstaining from answering the question, indicated by writing this in the space around the question or by crossing out or otherwise spoiling the question

2c) Are such figures available for the 1981, 1991 and 2001 censuses? If so, where may I read these?

3a) Will people who indicated that they do not have a single sex ever have their answer 'corrected' or 'resolved' to assign them a single binary sex?

3b) If so, what criteria will be used to assign this sex? How is this justified?

4) Approximately how many people had their answer for sex 'corrected' in the 1981, 1991 and 2001 census statistics for any reason?

Yours faithfully,

Nat Titman

Dear Office for National Statistics,

I made a Freedom of Information request of you on 14th of May, link here:


I have not received a response, nor any acknowledgement that the request was received or that you are working on gathering the requested information.

I am requesting an internal review to ensure that my request receives a prompt response.

Yours faithfully,

Nat Titman

Paul Wearn, Office for National Statistics

Our Reference: FOI01194/Titman/QE1

Dear Nat Titman

1a) Responses to the ***sex*** question, which has been asked since the
first UK Census in 1801, are used, together with age, as the basic
variable, by which the full range of other characteristics, such as
health, employment and unemployment in particular occupations and
industries, education levels, migration, etc are measured. Such
characteristics have always been measured by the sex as reported
subjectively by the respondent. Information on the category of transgender
is not specifically collected in the census since the small numbers
resulting would prevent ONS from disclosing any detailed statistical
information about them, even if a need had been expressed for the census
to collect such information.

1b) For the overwhelming majority of the population ***sex*** and
***gender*** will be the same, and no statistically significant
inaccuracies are introduced by conflating the two. Where someone has
ticked both options or left the question unanswered, a single response
will be created. This is not in any way intended to reflect the true
gender identity of any individual, it is simply done to ensure the
completeness of the final outputs as for every other census question
(except the question on religion which is voluntary). Note that the
scanned image of the original census record, which is stored for 100
years, will retain the original response.

2a) No, the census system does not accept answers to the ***sex***
question other than ***male*** or ***female***.

2b) i) Information on the number of instances of multi-ticking for any
question (including the question on sex) will be recorded, and could be
made available on request subject to the numbers not being disclosive,
once data processing is complete.

2b) ii) Item non-response for all questions (where respondents do not use
any tick or text boxes available) will be published as part of the data
quality report. If any other indication of being neither male or female
was specifically recorded, no figures will be available.

2b) iii-iv) No. This information would not be identified or captured in a
structured way, in the scanning process, although as noted above, the
scanned image will be retained and released in 100 years.

2c) Item non-response results for the 2001 Census are available on the ONS
website (which showed that 0.4% of the population did not answer the
question on sex), but none of the other information requested or item
non-response for 1981 and 1991 Censuses is available.

3a) The response as recorded on the questionnaire will not be changed.
However, the data processed from every such record will be edited to
assign the category ***male*** or ***female*** for statistical purposes.

3b) A probabilistic statistical system will assign the sex, based on other
characteristics. This system is called CANCEIS (Canadian Census Edit and
Imputation System), and is used by census offices worldwide.

The system identifies a "donor" record (someone who has answered the
question with a single tick, and has other similar characteristics) and
copies their response. This statistical method is known as

4) Information about edited records is not available for 1981 and 1991.
ONS has published imputation rates for each variable from 2001 on our
website at

Note that the imputation rate will include people who have left the
question blank and those who have ticked both male and female.
You have the right to have this response to your freedom of information
request reviewed internally by an internal review process and, if you
remain unhappy with the decision, by the Information Commissioner. If you
would like to have the decision reviewed please write to Frank Nolan,
Office for National Statistics, Room 1127, Government Buildings, Cardiff
Road, Newport, Gwent, NP10 8XG.

If you have any queries about this email, please contact me. Please
remember to quote the reference number above in any future communications.

Kind regards,

Paul Wearn LLB (Hons)
Legal Services
Office for National Statistics

For the latest data on the economy and society consult National Statistics
at http://www.ons.gov.uk

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not necessarily those of the Office for National Statistics


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