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Addressing for Census 2021

With the Census in England and Wales taking place on 21 March 2021, we created a programme of webinars to showcase our plans for design and quality assurance. The series, which was carried out through November and December 2020, included a high-level introductory overview as well as 'In Focus' sessions that outlined specific aspects in more detail. These webinars gave attendees the opportunity to ask questions and provide feedback

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Addressing for Census 2021

  1. 1. 1 Addressing for Census 2021 Welcome Please turn off your camera and mute your microphone Questions? Visit and enter code 14856 to ask your questions Technology problems? Email Starting at 2:15pm #Census2021
  2. 2. 2 Speakers Rob Doherty Census Statistical Design Address Lead #Census2021 14856
  3. 3. 3 Speakers Jon Wroth Smith Senior Statistician Census Statistical Design #Census2021 14856
  4. 4. 4 Why are we running these webinars? • To explain how the census works in collecting information and producing great statistics • To sign-post where more information is available • To follow on from the material we published in October • COVID response • Statistical Design • Findings from 2019 rehearsal #Census2021 14856
  5. 5. 5 Aims for this session: - Explain how ONS has created a high-quality address frame for Census 2021. - Indicate what considerations, checks and quality measures were used in the frame creation. - Highlight how the frame will continue to be updated and improved throughout the Census 2021 data collection phase #Census2021 14856
  6. 6. 6 Overview • Why addressing is integral to a successful census • What different addresses we’ve factored into the census design • How these have been collected, managed and assured • What planned continuous activity for addresses ONS has planned through operations and beyond #Census2021 14856
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  8. 8. 8 An Address Based Design Addresses are at the heart of the 2021 Census #Census2021 14856
  9. 9. 9 Addressing Overview – a few statistics • In England & Wales there are in excess of 26 million residential addresses • Last year there were more than 400,000 new residential addresses with 83,000 removed • Total number of addresses in AddressBase is 39 million addresses #Census2021 14856
  10. 10. 10 A few key definitions • Residential Household (HH) Address – Person or people with shared cooking facilities and shared living room or sitting room or dining area #Census2021 14856
  11. 11. 11 A few key definitions • Special Population Group (SPG) – Household addresses which may need a tailored enumeration approach because of security or access issues (e.g. royal households or family accommodation on military bases) or because we don’t have individual household addresses (e.g. caravans, boats and transient communities) #Census2021 14856
  12. 12. 12 A few key definitions • Communal Establishment (CE) – Managed residential accommodation such as care homes, student halls and prisons #Census2021 14856
  13. 13. 13 Address Frame #Census2021 14856
  14. 14. 14 Overview of the address frame • Address frame is the list of HH, SPG and CE which ONS use to make initial contact in 2021 Census • AddressBase is the basis for the frame supplemented by administrative sources • Quality measures for the frame have been defined as no more than 0.75% under coverage and no more than 1% over coverage #Census2021 14856
  15. 15. 15 Address Frame AddressBase Maintenance #Census2021 14856
  16. 16. 16 Address Frame AddressBase Extracts Used • Initial extract based on July 2020 snapshot (epoch) of AddressBase for main print run of contact letters • Second extract later, based on November 2020 snapshot of AddressBase for a second print run of contact letters • New addresses; invalid addresses & changes in address type from later updates of AddressBase will be used to update the Address Frame and field operation, before and during census #Census2021 14856
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  19. 19. 19 Address Index Matching Service (AIMS) • AIMS is an established tool to look up addresses online and will be used as part of electronic questionnaire • Uses a broader Address Index which includes address types other than those included on the Address Frame • Respondent facing version: • Changes from address provided • Usual residence (if visitor) • Address one year ago • Workplace address • Census processing version: • Matching of paper questionnaire responses to AIMS addresses #Census2021 14856
  20. 20. 20 Coverage – Clerical Check • ONS have expanded the size and scope of the clerical address resolution team in response to the COVID-19 pandemic • Clerical work involved investigating uncertain address using a range of online searches • Clerical checking supplemented by automating searches using algorithms based on sources found to be most useful in online searches • More addresses clerically checked and resolved than originally planned in the summer 2020 address check exercise #Census2021 14856
  21. 21. 21 Coverage – Clerical Check • Desk-Based clerical resolution steps 1. Data ‘buckets’ of uncertain address to clerical team 2. Put address into the AIMS tool (ONS Address Index Matching Service) 3. Check for Council Tax 4. Check Business Rates 5. Check Google Earth/ Maps 6. Google the address #Census2021 14856
  22. 22. 22 Coverage – Data Linkage • Data Linkage automated resolution steps 1. Clean and standardise ‘uncertain addresses’ extract (500k) from Epoch & the admin data 2. Use matching algorithm to link extract to Council Tax, VOA and Land Registry Prices Paid data 3. Flag linked records as real residential addresses 4. Reduces number of uncertain records to be checked manually 5. Include flagged records in the frame with confidence #Census2021 14856
  23. 23. 23 Supplementing AddressBase • ONS use a range of administrative and commercial data sources to supplement AddressBase for CEs and SPGs • Prisons (Ministry of Justice) • Armed Forces (Ministry of Defence / US Armed Forces) • Student Halls (Cushman & Wakefield) • Care Homes (Care Quality Commission and Care Inspectorate Wales) • Boarding Schools (Edubase) • Traveller Sites (Ministry of Communities and Local Government) #Census2021 14856
  24. 24. 24 Supplementing AddressBase • Clerical resource has most recently been used to supplement student halls with room level address information (where this is not provided on LLPG) – approximately 2,200 addresses • c.400,000 unit level addresses obtained. • Clerical checking has also been carried out to validate other CE types on AddressBase such as religious establishments and staff accommodation - approximately 2,800 addresses #Census2021 14856
  25. 25. Continual improvement 25 #Census2021 14856
  26. 26. 26 Post Census Address Frame Creation – Delta Address Frame Delta • Initial Address Frame loaded in October 2020 • QA of the Frame identified a number of small issues and inconsistencies with a small number of addresses • These will be updated along with changes between versions of AddressBase through the Address Delta in January 2021 #Census2021 14856
  27. 27. 27 Address Frame Undercount on frame • HH / SPG / CE can request an access code/questionnaire during census • Census Coverage Survey (CCS), sampled independently from Census. designed to identify any missed addresses to be accounted for in coverage estimation #Census2021 14856
  28. 28. 28 Address Frame Overcount on frame • Addresses which no longer exist will be undeliverable • ONS will use admin data (such as Council Tax) in the process of evaluating where addresses have not returned, including those which are flagged as potentially vacant • Field officers will identify addresses as vacant or derelict during visits to non-responding households #Census2021 14856
  29. 29. 29 Post Census Address Frame Creation – Collection • Address Resolution • The design of the Census 2021 Collection operation provides opportunities for respondents to inform us of differences between their address and our records. • Processes are in place to handle address change scenarios such as: • ‘New’ addresses • Split addresses • Merged addresses • Changes in address type (HH to CE; CE/SPG to HH etc.). • This allows for the real-time updating of the Census Address Frame; and is intended to allow households and individuals flexibility in how they respond and complete their Census form. These address changes will also be reflected in the statistical outputs produced #Census2021 14856
  30. 30. 30 Summary • A high quality census needs a high quality address frame • The Address Frame for Census 2021 has been created using high quality and timely data sources • The Address Frame and Field Operation for Census 2021 has been designed to reflect the complexities and challenges of addressing varied accommodation types • Census collection has been designed to flexibly respond to these complexities • Improvement of the Address Frame will continue throughout preparations and collection for the Census, and beyond including through CCS. #Census2021 14856
  31. 31. 31 Addressing for Census 2021 Any questions? Visit and enter code 14856 Please complete our evaluation survey (we’ll email you a link) and let us know how we did. If you have any questions email us on Want to learn more about the Census 2021 Statistical Design? Visit our website to find out more about our other webinars. #Census2021