1. Executive summary

In December 2018, the government presented to Parliament a White Paper Help Shape our Future: The 2021 Census of Population and Housing in England and Wales (PDF, 967KB). This outlined the Office for National Statistics’ (ONS’s) proposal to collect information on date of birth, sex, marital and civil partnership status, and household relationships to meet the requirement for information on the population structure to understand for example future hospital, school, and housing needs.

We will use the 2011 Census question topics on demography for Census 2021 and collect these data in a way that is consistent with previous censuses. The questions used to collect data on demography are:

  • date of birth
  • sex
  • marital and civil partnership status
  • household relationships

The question on sex is not discussed in this report; information on the development of this question is in the Sex and gender identity question development for Census 2021.

Census 2021 will be an online-first census, with a target of 75% online returns. We have reviewed and tested each question online and have recommended additional design and functionality amendments specific to the electronic questionnaire. We have also recommended additional changes to the question designs following our stakeholder engagement, evaluation and testing programmes. These changes will be detailed in this report.

The main recommended changes to question designs are:

  • the marriage and civil partnership question, will be a new two-stage question design in Census 2021, whereby the first stage collects the legal status and the second stage asks if the respondent is, or was, in a marriage or civil partnership with someone of the opposite or same sex

  • we have updated the marriage and civil partnership question to reflect that civil partnerships will be available to opposite-sex couples by Census 2021

  • in the household relationship question, we have updated the response option “Same-sex civil partner” to “Legally registered civil partner” and added instructions to include half-brother or sister to the “brother or sister” response option

  • we have added extra guidance on the paper questionnaire to aid respondents answering the relationship matrix grid on paper

  • the household relationship question collects relationships between household members between every five people on paper and for the electronic questionnaire, which was previously every six people

  • the paper questionnaire captures the relationship between household members through a matrix, whereas on the electronic questionnaire this information is collected through page by page questions and response options, to meet government digital service’s service standards

Any additional changes to question designs, including online functionality and accessibility, will be detailed in the sections Research that led to the 2018 White Paper recommendations and Research that led to the recommended Census 2021 question designs.

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2. Aim of question development report

Since the publication of the White Paper, the Office for National Statistics (ONS) has conducted and concluded the final phase of testing on the demography questions.

This report provides links to previously published research and the findings of additional testing that led to the final recommended questions for Census 2021 in England and Wales. The questions and response options for Census 2021 have now been finalised through the census secondary legislation: the Census (England and Wales) Order 2020, and Census Regulations for England and for Wales.

The evidence base for the recommendations made in the White Paper and the finalisation of the date of birth questions for Census 2021 is discussed in the section Research that led to the 2018 White Paper recommendations. Further research into the relationship matrix and marital status questions are discussed in the section Research that led to the recommended Census 2021 question designs.

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3. Research and development timeline

In June 2015, the Office for National Statistics (ONS) held a formal, 12-week consultation process asking census users for their views on the topics that were required in the questionnaire in England and Wales. The aim of the consultation was to promote discussion and encourage the development of strong cases for topics to be included in Census 2021.

In May 2016, we published our response to the 2021 Census topic consultation. This set out our updated view on the topics to be included in Census 2021, including:

  • a summary of proposals for new topics
  • next steps
  • an overview of our plans

A detailed summary of the consultation responses relating to the topic of demography can be found in the Demography topic report (PDF, 1.6MB). In this report, we made clear commitments to the public. These were to ensure the marital and civil partnership status questions were kept up-to-date and in line with current legislation, such as the Marriage (Same Sex Couples) Act, 2013 and the Civil Partnerships, Marriages and Deaths (Registration Etc.) Act 2019. Also, to improve the respondent experience, reduce the respondent burden and investigate ways to improve data quality for the marital and civil partnership status question.

We have provided an update on how we met these commitments in Annex 1.

Overall, respondents to the consultation reported that the census is their main source of detailed information on each of these topic areas, which informs vital population estimates and projections and therefore underpins decision making, planning and resource allocation across central and local government. The information collected from these topics also effectively informs targeting of services and resource allocation for specific groups within the population. Additionally, age, sex, and marital and civil partnership status are protected characteristics under the Equality Act 2010.

Following this, we began a comprehensive programme of research and development. We provide a full list of the tests used in the development of the topic of demography in Annex 2. Further details are provided in the summary of testing for Census 2021.

The tests utilised a range of qualitative and quantitative research methods. A short description of the different research methods and sampling techniques is given in the question and questionnaire development overview for Census 2021. Testing included respondents from a wide range of backgrounds. This included differing marital and civil partnership statuses and ages.

In December 2017, we published a further census topic research update, which highlighted progress of the work on the legal marital or civil partnership question, and on the relationship matrix question.

In December 2018, the government presented to Parliament a White Paper Help Shape our Future: The 2021 Census of Population and Housing in England and Wales (PDF, 967KB). This outlined our proposals for the topics of date of birth, marital and civil partnership status, and household relationships. These were to:

  • collect information on name, sex and date of birth
  • collect information on family relationships for households with two or more people
  • conduct testing to review the marital status question and response options to ensure all the necessary data are collected and seek to ensure that all legally recognised statuses are covered
  • consider next steps for the marital and civil partnership status question response options in the light of the government’s response to the Supreme Court judgement concerning the availability of civil partnerships to opposite-sex couples

Alongside the White Paper we published a further Census topic research update. This provided additional details of the research that supported the demography recommendations announced in the White Paper.

The question recommendations for Census 2021 are now finalised. We have evaluated the questions on demography for potential impact on data quality, public acceptability, respondent burden, financial concerns and questionnaire mode. We present details of this evaluation in Annex 3.

Annex 4 provides details of the definitions and terms used in this report.

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4. Research that led to the 2018 White Paper recommendations

The starting point for reviewing the questions was the 2011 Census question designs. You can see these questions on the 2011 Census Household Questionnaire (PDF, 1.8 MB).

As set out in the White Paper Help Shape our Future: The 2021 Census of Population and Housing in England and Wales (PDF, 967KB), with further details provided in the December 2017 and December 2018 census topic research updates, we reaffirmed our commitment to asking questions on date of birth, marital and civil partnership status, and household relationships.

This section provides the details on how the questions on date of birth evolved from the beginning of testing through to the final recommended questions for Census 2021.

References to tests are provided in the form (Year: Test number). For example, the fifth test conducted in 2017 is referenced as (2017:5).

Date of birth

A question on age has been included since at least the 1841 Census (the first to ask detailed information about individuals) and date of birth since the 1939 Identity Card Registers for England and Wales.

There are no changes to the 2011 Census date of birth question stem on the paper questionnaire for Census 2021.

2011 Census date of birth question

What is your date of birth?
Day    Month    Year
[ ]      [ ]      [ ]

Electronic questionnaire

The electronic questionnaire date of birth question will use validation to ensure a valid date has been entered. The earliest date that can be entered is 21/3/1906 (115 years old), the latest date that can be entered is census day 21/3/2021. Additionally, there is an example text above the data entry fields that advises respondents on the correct format to use to supply their date of birth:

“for example, 31 3 1980”

Confirmation of age question question

Date of birth is crucial for the collection of demographic information critical across a wide range of census uses. Age is derived from date of birth and derives the age at a person’s last birthday (mid-year and census day). The variable informs population estimates and projections and therefore underpins decision making, planning and resource allocation across central and local government. Age is vital for multivariate analyses for the vast majority of users and is a protected characteristic under the Equality Act 2010.

In the 2011 Census, the agreement rate for date of birth question was 98.4% (single year) and 99.3% for five-year age bands, suggesting there was some inaccuracy in date of birth information. It is known in survey design that some people use “today’s” date for their date of birth in error, or mis-calculate the year of birth, particularly when answering on behalf of someone else.

Question design for online

In addition to the testing described earlier, the demography questions have undergone significant user experience (UX) testing (2017:2, 2018:2, 2019:1, 2020:2). UX testing focuses on understanding user behaviours as people interact with online services. Through observation techniques, task analysis and other feedback methodologies, it aims to develop a deep knowledge of these interactions and what it means for the design of a service.

UX research has taken place on a rolling, ongoing basis since 2017 and the programme will continue through 2020. All participants are purposively selected to include a wide range of ages and digital abilities across the country.

UX testing included various iterations of the demography questions described elsewhere in this report. Feedback from this research informed decisions made on the design of these questions. For more information on UX testing, see the Question and questionnaire development overview for Census 2021.

We tested adding a confirmation of age question on the electronic questionnaire to increase the accuracy of dates entered in the date of birth question. Findings from user research testing (2017:2, 2018:2, 2019:1, 2020:2) suggested the additional page to confirm respondents age helped, and made some respondents go back to the date of birth question to correct the digits entered.

We recommend using the following confirmation of age question.

You are XX years old. Is this correct?

[ ]    Yes, I am XX years old
[ ]    No, I need to change my date of birth

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7. Annex 1: Census commitments made on the topics of demography

In the 2021 Census topic consultation response, the Office for National Statistics (ONS) made clear commitments to the public. We committed to continuing to ask the questions on date of birth, marital or civil partnerships status and household relationships. We also made the following commitments:

Commitment to ensure the marital and civil partnership status questions were kept up-to-date and in line with current legislation

We updated the marital and civil partnership status questions so that they would reflect possible changes to the law that allow same-sex couples to marry and opposite-sex couples to register a civil partnership introduced by the Marriages (Same Sex Couples) Act, 2013 and Civil Partnerships, Marriages and Deaths (Registration Etc.) Act 2019.

Improve the respondent experience, reduce the respondent burden and investigate ways to improve data quality

We met these commitments by extensively testing the household relationships question to ensure the question is designed to minimise respondent burden. We were helping respondents to enter household relationships more easily online by using names instead of placeholders (for example, we used “Thinking of John Smith…” instead of “Thinking of Person 1…”) to help them enter the household relationships more easily.

We ensured the marital and civil partnerships status questions were considered acceptable by a large majority of respondents, and that they did not result in an unacceptable number of dropouts from the questionnaire.

We tested various possible layouts of the date of birth question for the online questionnaire to find the design that would give us the best data quality with the least respondent burden. We then used the date of birth data entered online to calculate age and therefore enabling respondents to check their answers.

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8. Annex 2: Summary of research undertaken for the topic of demography, 2017 to 2019

References to tests take the form (Year: Test number). “Year” refers to the calendar year the test was undertaken in and the test number is the position of the test within the year considering all testing that took place in that year. For example, the fifth test conducted in 2017 would be referenced as (2017:5).

A full description of each of these items can be found in summary of testing for Census 2021.

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9. Annex 3: Question evaluation

Evaluation of date of birth question

The potential impact for the date of birth question on data quality, public acceptability, respondent burden and financial concerns were assessed as “low”.

Potential for impact on questionnaire mode: “Medium”

The online question does not allow respondents to proceed without having answered the date of birth question. Furthermore, the online question is broken into two sections, first asking for date of birth and then asking the respondent to confirm their age calculated from the information given in the date of birth question. These differences between paper form and electronic questionnaire led to the potential impact on questionnaire mode being assessed as “medium”.

Evaluation of marital and civil partnership status question

The potential impact for the marital and civil partnership status question on data quality, public acceptability, respondent burden and financial concerns were assessed as “low”.

Potential for impact on questionnaire mode: “Medium”

The question on the electronic questionnaire has radio buttons and therefore prevents multi-ticking, however, more than 1% of respondents select multiple response options on the paper form. These differences between paper form and electronic questionnaire led to the potential impact on questionnaire mode being assessed as “medium”.

Evaluation of married or in a registered civil partnership with question

The potential impact for the married or in a registered civil partnership with question on data quality, public acceptability, respondent burden and financial concerns were assessed as “low”.

Potential for impact on questionnaire mode: “Medium”

The second stage of the marital and civil partnership status question asks again for sensitive information with the potential of respondents choosing a more socially acceptable response option, social desirability answers reduce when answering online. The question displayed on the electronic questionnaire depends on the response option chosen in the first stage of the marital and civil partnership status question and therefore looks different. In addition, the question on the electronic questionnaire has radio buttons and therefore prevents multi-ticking. All of these differences between paper form and electronic questionnaire led to the potential impact on questionnaire mode being assessed as “medium”.

Evaluation of household and family relationships question

The potential for impact on data quality, public acceptability and financial concerns have been assessed as “low”.

Potential for impact on respondent burden: “Medium”

On the paper questionnaire, the respondent must restate the names of household members, which is used to help respondent understanding of the question. On the electronic questionnaire, the names of other household members are piped into the question stem, however some respondents did not understand the question or the type of answer that was expected. There is also a lot of repetition in the question stem and responses. Therefore, the potential for impact on respondent burden has been assessed as “medium”.

Potential for impact on questionnaire mode: “Medium”

During testing (2018:42), there were more errors on the electronic questionnaire because of respondents misunderstanding or not reading the question stem. Once these errors were identified by the respondent, they would return to review the first stage of the multi-stage question. The paper questionnaire has a name write-in, while the electronic questionnaire will pipe in names to the question stem automatically. The two modes have different instructions and are visually different from one another. Therefore, the potential for impact on questionnaire mode has been assessed as “medium”.

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