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. This outlined the Office for National Statistics's (ONS's) recommendation to collect information on the topics of second address, migration (including short-term, long-term and internal migration) and citizenship.

This would meet the need for population estimates and projections down to the local level that underpin planning and resource allocation. These question also contribute to our understanding of internal and international migration by helping us to arrive at a usual resident base.

The questions used to collect data on the topics of second address, migration and citizenship are:

  • second address and second address type

  • full-time education and term-time address

  • country of birth, date of arrival in the UK and intended length of stay in the UK

  • usual address one year ago

  • passports held

The main changes to questions designs from those used in the 2011 Census are:

  • adding guidance to the second address question to help respondent understanding

  • adding a "Partner's address" response option to the second address type question

  • combining the response options "Less than 6 months" and "6 months or more but less than 12 months" into a single option "Less than 12 months" on the intended length of stay in the UK question

As Census 2021 will be online-first, the question development also covers the online development research and testing of these questions.

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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 topics of second address, migration and citizenship.

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 finalisation of the questions for Census 2021 is discussed in Section 4: 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 stakeholders 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, the ONS published its 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

This response included a commitment to continue to collect information on migration (including long-term, short-term and internal migration) and citizenship. We also made a commitment to maintain the same enumeration bases as used in 2011. These included:

  • the second residence population

  • the out of term-time population

  • short-term residents

Production of these enumeration bases requires the continued collection of information on second address, including term-time address.

A detailed summary of the consultation responses relating to the topic of migration can be found in the migration topic report (PDF, 1.7 MB). In this report, the ONS made clear commitments. We have provided an update on how we met these commitments in Annex 1.

Following this, we began a comprehensive programme of research and development. We have provided a full list of the tests used in the development of the the questions on second address, migration and citizenship 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 participants from a wide range of backgrounds, including short-term and long-term international migrants, schoolchildren and students, and people who stay at a second address.

The questions for Census 2021 have now been finalised. We have evaluated each question for its potential impact on data quality, public acceptability, respondent burden, financial concerns and questionnaire mode. We have presented details of this evaluation in Annex 3.

The questions on second address, migration and citizenship are fundamental to achieving census definitions of a usual resident base. You can find out more about these definitions in Output and enumeration bases: residential address and population definitions for Census 2021.

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6. Next steps

Address look-up

We are developing address lookup technology for the electronic questionnaire. This will allow users to enter their postcode or first line of their address, then select their house from a list. This will reduce respondent burden, particularly when entering an address that is not the respondent's current permanent address. The functionality will also help to reduce input errors, which will reduce the processing required.

We have recommended that the technology is used for the following second address and migration questions in Census 2021:

  • second address (when in the UK)

  • term-time address (when "another address" and no second address has been provided)

  • usual address one year ago (when in the UK)

The exact wording of the address look-up will be finalised as part of this work.

Search-as-you-type

We are developing search-as-you-type technology for the electronic questionnaire. We present more details of this functionality in the Question and questionnaire development overview for Census 2021.

The exact wording of the search-as-you-type will be finalised as part of this work.

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7. Annex 1: Census commitments made on the topics of second address, migration and citizenship

In our response to the 2021 Census topic consultation, the Office for National Statistics (ONS) committed to collecting data on long-term migration, short-term migration, internal migration and citizenship. We also made the commitment to explore how the online question set can improve the collection of the data while still meeting user needs.

The data collected on the electronic questionnaire are the same as on the paper questionnaire. However, where relevant, we have provided additional guidance, updated question designs and implemented automatic routing to improve accessibility and reduce respondent burden. The easier a respondent finds the questions to answer, the better the data quality will be.

We are developing address look-up and search-as-you-type functionality for the electronic questionnaire. Although this functionality increases the differences between the electronic and paper questionnaires, this will mean that respondents completing the questionnaire online will find it easier and quicker to answer questions.

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8. Annex 2: Summary of research undertaken for the topics of second address, migration and citizenship, 2017 to 2020

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

All questions meet our thresholds to ensure reliable information will be collected in Census 2021.

A question that has been assessed as having a "High" potential for impact is closer to the threshold for exclusion from the census than a topic that has been assessed as having a "Low" potential for impact.

Second address

The second address question has been assessed as having “Low” potential for impact on public acceptability and financial concerns.

Potential for impact on data quality: “Medium”

This question collects information that cannot be directly observed, which can cause data quality issues when answering on behalf of another person. Feedback from the 2019 Rehearsal (2019:15) showed that some respondents found this question hard to answer. Around 10% of online respondents, well above the average seen in other questions, used the “Previous” button to go back and review their answer to this question.

Potential for impact on respondent burden: “Medium”

This question contains a write-in field, which can increase respondent burden. However, in Census 2021 on the electronic questionnaire, respondents will be able to use standard postcode look-up functionality to find addresses without typing them out in full, which can help reduce respondent burden.

Feedback from the 2019 Rehearsal (2019:15) showed that some respondents found this question difficult to answer, and use of the “Previous” button on the questionnaire was high.

Potential for impact on questionnaire mode: “High”

On the paper questionnaire, respondents are able to write in the address or country of the second address within the response options. On the electronic questionnaire, respondents enter the address or country on a separate screen. When entering a UK address on the electronic questionnaire, respondents will be able to use standard postcode look-up functionality to enter addresses using the postcode and street address.

Second address type

The second address type question has been assessed as having a “Low” potential for impact on public acceptability, financial concerns and questionnaire mode.

Potential for impact on data quality: “Medium”

This question collects information that cannot be directly observed, which can cause data quality issues when answering on behalf of another person.

Feedback from the 2019 Rehearsal (2019:15) showed that some respondents found this question difficult to answer, and this was backed up by quantitative data that showed respondents spent more time answering this question than was expected for a question of this type.

Potential for impact on respondent burden: “Medium”

This question has more response options than in the 2011 Census, which has increased respondent burden. Results from the 2019 Rehearsal (2019:15) showed that respondents found this question difficult to answer and, on average, took a longer time than expected to answer this question.

Evaluation of the full-time education and term-time address questions

The full-time address type and term-time address have been assessed as having “Low” potential for impact on data quality, public acceptability, respondent burden, financial concerns and questionnaire mode.

Evaluation of the country of birth question

The country of birth question has been assessed as having “Low” potential for impact on data quality, public acceptability, respondent burden and financial concerns.

Potential for impact on questionnaire mode: “Medium”

On the paper questionnaire, respondents write in their country of birth within the “Elsewhere” response option. On the electronic questionnaire, if respondents choose the response option “Elsewhere” then they will enter the country on a separate screen. The write-in response option has search-as-you-type functionality; a list of suggested countries will appear once the respondent starts to type a response.

Evaluation of the date of arrival in the UK question

The date of arrival in the UK question has been assessed as having “Low” potential for impact on public acceptability and financial concerns.

Potential for impact on data quality: “High”

This question requires respondents to recall a date in the past, which can cause data quality issues. In addition, this question is not observable and can be considered a sensitive subject and so may cause issues when answering on behalf of another person.

Data from the 2019 Rehearsal (2019:15) showed that respondents took a longer time, on average, to answer this question and this question had a relatively high, above 7%, non-response rate.

Potential for impact on respondent burden: “Medium”

This question has a write-in option and requires respondents to recall a date in the past, which can increase respondent burden. Respondents must answer this question so that they can be correctly routed to the next question. Feedback from the 2019 Rehearsal (2019:15) showed that some respondents reported that the question was difficult to answer, expecially when the date was a long time ago, and quantitative data showed that non-response and time taken to answer this question were above the expected levels.

Where the month of arrival is one year prior to the census date, 21 March 2020, respondents will be required to answer a follow-up question to identify whether they have stayed over one year or less than one year.

Potential for impact on questionnaire mode: “High”

The question stems on the paper and electronic questionnaire differ slightly. Also, on the electronic questionnaire the respondents are asked a separate question (“Did you arrive in the UK on or after 21 March 2020?”) to enable routing to the next question on intended length of stay. This question does not appear on the paper questionnaire except as a routing instruction (for example, “If you arrived before 21 March 2020, go to 13”).

This question also has hard validation on the electronic questionnaire, meaning respondents must give an answer; however, on the paper questionnaire this type of validation is not possible. Results from the 2019 Rehearsal (2019:15) showed that this question had a non-response rate of over 1% on paper.

Evaluation of the intended length of stay in the UK question

The intended length of stay in the UK question has been assessed as having “Low” potential for impact on public acceptability and financial concerns.

Potential for impact on data quality: “Medium”

This question is difficult to answer on behalf of another person. Feedback from the 2019 Rehearsal (2019:15) showed a high non-response rate, above 7%, and that some respondents reported difficulties in answering this question.

Potential for impact on respondent burden: “Medium”

Some respondents in the 2019 Rehearsal (2019:15) reported that they found this question dififcult to answer. The question had a high non-response rate and more than 2% of respondents used the “Previous” button to go back to review their answer, suggesting this question was burdensome to respondents.

Potential for impact on questionnaire mode: “Medium”

The electronic questionnaire uses radio buttons to ensure respondents only give one answer, but this is not possible on the paper questionnaire. Respondents are required to give an answer on the electronic questionnaire; however, this type of validation cannot be enforced on the paper questionnaire.

In addition, this question could be subject to social desirability bias, which is where people respond in a way that they consider socially acceptable, rather than what they believe to be true. Responses to the paper questionnaire are more at risk from this type of behaviour as they are more easily read by other members of the respondent’s household than those on the electronic questionnaire.

Evaluation of the usual address one year ago question

The usual address one year ago question has been assessed as having “Low” potential for impact on data quality and public acceptability.

Potential for impact on respondent burden: “Medium”

The question has long response options and may require the respondent to write in a response. In addition, this question could be difficult to answer on behalf of another person.

Potential for impact on financial concerns: “Medium”

All write-in responses require additional processing, which adds cost to the census. In the 2011 Census, 11.5% of respondents used the write-in response for the question on usual address one year ago. However, the introduction of postcode look-up functionality on the electronic questionnaire should reduce the manual processing required for this question.

Some respondents may have privacy concerns about sharing their address one year ago with other members of their household. This could lead to requests for individual forms, which come with additional postage and processing costs for the census.

Potential for impact on questionnaire mode: “High”

This question has multiple stages on the electronic questionnaire but appears as one question on the paper questionnaire. On the paper questionnaire, respondents have to write in the address but on the electronic questionnaire respondents are able to use postcode look-up functionality.

On the paper questionnaire, it is possible to select two or more mutually exclusive options, while the electronic questionnaire only allows for one option to be selected.

Evaluation of the passports held question

The passports held question has been assessed as having “Low” potential for impact on data quality, public acceptability, respondent burden and financial concerns.

Potential for impact on questionnaire mode: “Medium”

This question has instructions, in an include panel, helping respondents to answer this question on the electronic questionnaire. Because of space constrants, these instructions do not appear on the paper questionnaire.

On the electronic questionnaire, respondents can write in the country of their passport or select from a list of suggested countries that appears after they have typed a few characters (search-as-you-type functionality).

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10. Annex 4: Definitions and terms used in this report

Second address

A second address is any single address where a person has stayed for more than 30 days in the past year that is not their usual residence. This can be 30 days in a row or 30 days separated across the year.

Schoolchildren at boarding school and students

Schoolchildren at boarding school and students who stay at their term-time address for four or more nights per week (in general) should be counted as usually resident at their term-time address and complete the census form at that address. These students and schoolchildren should also be counted as usually resident at their permanent or family address (where this is not their term-time address), and only some information will be collected on the census form.

Schoolchildren at boarding school and students who stay at their term-time address for three nights or fewer per week (in general) should be counted as usually resident at their permanent or family address. They should not complete the census form at their term-time address.

This definition has changed from the 2011 Census to accommodate an increase in part-time boarders and flexi-boarders. We detail this change in definition in the Output and enumeration bases: residential address and population definitions for Census 2021 report.

Migration

The UN definition of a long-term migrant is a person who changes his or her country of usual residence for a period of at least 12 months. The country of destination effectively becomes the country of usual residence. The Office for National Statistics (ONS) uses this time period to distinguish short- and long-term residents.

The ONS has adopted these definitions for counting long- and short-term migrants in Census 2021 in England and Wales.

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