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Addressing for Census
2021
Welcome
Please turn off your camera and mute your microphone
Questions?
Visit www.sli.do and enter code 14856 to ask your questions
Technology problems?
Email sdr.stakeholder.engagement@ons.gov.uk
Starting at 2:15pm
#Census2021

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Speakers
Rob Doherty
Census Statistical Design
Address Lead
#Census2021 www.sli.do 14856

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Speakers
Jon Wroth Smith
Senior Statistician
Census Statistical Design
#Census2021 www.sli.do 14856

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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 www.sli.do 14856

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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
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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
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An Address Based Design
Addresses are at the heart of the 2021 Census
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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
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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
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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)
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A few key definitions
• Communal Establishment (CE) – Managed residential
accommodation such as care homes, student halls and prisons
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Address Frame
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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
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Address Frame
AddressBase Maintenance
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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 www.sli.do 14856

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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
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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
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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 www.sli.do 14856

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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
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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)
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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 www.sli.do 14856

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Continual improvement
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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 www.sli.do 14856

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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
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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 www.sli.do 14856

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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 www.sli.do 14856

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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 www.sli.do 14856

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Addressing for Census
2021
Any questions?
Visit www.sli.do 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 SDR.stakeholder.engagement@ons.gov.uk.
Want to learn more about the Census 2021 Statistical Design? Visit our website to find out
more about our other webinars.
#Census2021