2021 Census Outputs and Dissemination: Introduction

2021 Census Outputs and Dissemination:
Introduction
2021 Census outputs roadshows
Spring 2018

Aims for today
• Outline of 2021 Census outputs strategy as detailed in
our ‘Initial View on 2021 Census Output Content Design’
consultation launched at the end of February 2018
• Provide a demonstration of our current prototype of a
flexible dissemination system
• Update on our plans for enhanced census outputs
• Answer your questions and get feedback on our plans
for outputs

Session outline
13:30 – 13:45 Introduction to 2021 Census Outputs
13:45 – 14:15 Outputs Consultation
14:15 – 15:30 Flexible Dissemination System
Includes:
 Presentation
 Coffee break
 Try out the flexible table builder prototype
 Visit market stalls to find out more about other
2021 Census outputs
15:30 – 16:00 Enhanced Census Outputs
16:00 – 16:15 Wrap-up and questions
Next steps

Vision for 2021 Census Outputs
Flexible Timely Accessible

Analysis Programme
• Make the best use of census data, alongside
administrative and survey data to describe the
society we live in
• Add value by helping users understand and
interpret census data
• Statistical bulletins, interactive visualisations etc
• Currently being developed

Future User Engagement
Type of
Engagement
User
Research
Public
Consultation
Working
Groups
???
UKCC / UK
Harmonised
Working
Group
Conferences
User Groups
ONS staff

Any questions:
census.outputs@ons.gov.uk

Initial View on 2021 Census Output Content
Design: Public consultation
Spring 2018

Overview
• Initial high-level plans for 2021 Census output content
design and dissemination (England and Wales only)
 Outline our vision for 2021 Census outputs
 Our first step towards understanding what users
require from 2021 Census outputs
 Proposal at present
 Feedback will help inform our future research and
development of these outputs

Consultation open:
28th February – 23rd May 2018
https://consultations.ons.gov.uk/census/initial-view-
on-the-2021-census-output-design

Flexible Dissemination System
• Web-based interactive dissemination system
 Define own queries
 Select geography, population base and variables
required
• Pre-determined univariate tables
More details in next session

Enhanced Census Outputs
• 2021 Census-based outputs where census
data and administrative data are linked at the
record level to enable the production of
multivariate, small area outputs
More details in a later session

UK Harmonisation and UK Statistics
• Working with NRS and NISRA to harmonise
wherever possible
 Statistical disclosure control
 Dissemination approach
 Metadata
• Exploring how we provide UK data to users

Microdata
Public 1% sample - individuals
Accessed via ONS website
Safeguarded 2x5% sample – individuals
Accessed via UKDS
Secure 10% sample – individuals and household
Accessed via ONS SRS at ONS Titchfield,
Newport, London
2011:
• Requirements for safeguarded household file
• Review sample design and size
• Microdata Working Group

Origin-Destination
• Review statistical disclosure control methodology
• Aim to make more data publically available
• Consider number of tables produced
• Origin-destination Working Group
Migration Residence
Workplace Student

Accessing sensitive census data
• Provide access to sensitive census data in
secure and controlled research environments
• Access granted in accordance with ONS
Approved Researcher Scheme
• Continue to review locations and access
arrangements
• Longitudinal Study – 1% sample

Output categories and population bases
Output categories
• Topics - research is ongoing
• Recommendations to inform White Paper in
2018
Population bases
• Continue to use 2011 population bases
Small populations
• Continue to identify value and dissemination

Geography
Output Areas and Workplace Zones
• Continue to be building blocks for census geographies
• Keep maintenance to within 5%
Grids
• 2011 – 1km square grid for Eurostat using postcode-level
population estimates
• Explore user requirement for grids
Civil parishes
• 2011 – 10% parishes without data
• Identify methodology to make more data available for
parishes

Interpreting 2021 Census results
Metadata
• Will continue to produce metadata
• Will consider best way to provide this based on
the dissemination system
Quality Assurance
• National Statistics Accreditation
• Population estimates

Evaluation
• Strength of impact (positive, negative or none) of
our intended design on:
Accessibility
Flexibility
Timeliness of outputs for users
• Evidence used to identify the most important
concerns for users and prioritise research on
these aspects

Public good
• Work being undertaken to “serve the public
good”
 using census data for public policy decision making
 using census data for public service planning and
delivery
 using census data for allocation of public resources
 using census data for decisions which are likely to
significantly benefit the UK economy, society or
quality of life of people in the UK

Example response to consultation
As a private sector transport provider we worked with
local authorities [insert name of LA] in our region to
identify where a new bus route should be placed.
We required access to safeguarded and secure origin-
destination data as we needed to know where residents
lived and worked and how many cars they owned.
We were unable to easily access the safeguarded and
secure origin-destination data as we are based in the
North West and the VML is in Newport, London, Titchfield.
This caused us 12 month delay in the project to enable
time to travel to these locations and ££ in extra transport
costs to travel to these locations.
Once we did access the data, because it was 5 years after
census day, it was out of date.

Consultation open:
28th February – 23rd May 2018
https://consultations.ons.gov.uk/census/initial-view-
on-the-2021-census-output-design
Any questions:

Flexible Dissemination System
Spring 2018

Presentation Overview
• Our Aims for 2021 Census Outputs
• How we propose meeting those aims
• The benefits
• The trade-offs
• Where we are - the prototype
• What’s next ?
• Hands On Session
• Other Activities

Aims: Designed based on User Feedback

Proposal: Fast & Flexible Dissemination
Statistical disclosure control:
Aims to ensure that statistical outputs provide
as much utility to users, whilst maintaining the
confidentiality of individuals, households, etc.
Automated
checks

Statistical Disclosure Control
Automated
checks
The type of automated SDC checks we are looking at are:
•Maximum number of cells
•Maximum number of variables
•Small values in totals
•Percentage of cells that are populated
•Percentage of cases in one cell/row/column
•Real/fake 1s and attribute disclosures
Checks and parameters have not been finalised yet.
Record swapping and cell key information is on the display

Is this possible?
• Prototype developed by ONS with Sensible Code Co.
• User interface – for demonstration purposes only
• Automated Statistical Disclosure Control embedded.
• 60m record artificial database grossed up from a 2011
Census Microdata Sample
• 8 levels of Output Area geography hierarchy (181,408
OAs)
• 80 variables incl. person and household characteristics

Here is an example….
Number of areas for which data
will be released

Pass or Fail? - Same Query for Different Areas
Number of areas for which
data will be released

?
??
?
?
So… what are the benefits?
Users can
define their
own data
query
All standard
outputs
available from
one place
More detail
for some
small areas
Wider benefits for
data
dissemination
across the GSS
Multivariate data
earlier than before

The benefits come with some trade offs
• The protection added to reduce the potential for
“differencing” between similar tables is given by the
“cell-key method”.
• Small inconsistencies will exist in the totals
between different tables
• These inconsistencies can occur in two
ways………

Summing of Individual Cells
Ethnicity by occupation at local authority level
LA=1 Occupation
Ethnicity: 1 2 3 4 5 6 7 8 9
White 3885 6014 4325 5726 5202 4172 4394 4282 6784 44784
Mixed 27 55 64 44 47 53 70 34 70 464
Asian 198 357 134 168 171 135 292 233 294 1982
Black 23 93 42 49 34 76 44 38 97 496
Chinese 23 40 11 6 25 15 23 15 33 191
4156 6559 4576 5993 5479 4451 4823 4602 7278 47917
Ethnicity by occupation at Output Area level aggregated to local authority level
LA=1 Occupation
Ethnicity: 1 2 3 4 5 6 7 8 9
White 3886 6012 4324 5730 5205 4171 4391 4276 6784 44779
Mixed 27 57 66 43 48 52 68 35 70 466
Asian 196 359 133 166 172 137 292 231 291 1977
Black 23 93 41 48 33 76 44 41 94 493
Chinese 22 40 11 5 25 15 24 15 32 189
4154 6561 4575 5992 5483 4451 4819 4598 7271 47904
E.g. Local Authority total
White ethnic group
category:
Total for row at local
authority level is 44,784
Total for row in Output Area
aggregation is 44,779
Difference of 5
vs Sum of aggregated output areas

Tables Sharing a Common Variable
Age by marital status at local authority level
LA=1
Single Married Separated Divorced Widowed Total:
0-15 12176 0 0 0 0 12176
16-24 8313 207 11 13 8 8552
25-34 5249 2439 241 199 20 8148
35-44 2886 4468 403 914 44 8715
45-54 1517 5355 432 1521 160 8985
55-64 613 5312 223 1257 426 7831
65-74 308 3769 105 659 930 5771
75+ 274 2030 38 251 2357 4950
Total: 31336 23580 1453 4814 3945 65128
Age by ethnic group at local authority level
LA=1
N.A. White Mixed Asian Black Chinese Total:
0-15 89 10146 420 1179 233 107 12174
16-24 568 6946 186 679 106 67 8552
25-34 23 6895 145 822 158 106 8149
35-45 3 7810 87 581 178 57 8716
45-54 3 8378 83 393 96 34 8987
55-64 0 7518 37 227 29 20 7831
65-74 0 5612 15 111 26 8 5772
75+ 0 4856 13 54 22 4 4949
Total: 686 58161 986 4046 848 403 65130
0-15 Age category:
total for row by ethnic
group is 12174
total for row by marital
status is 12176
Difference of 2
E.g. Age by ethnic group
vs Age by marital status

Aims: Recap
Access to more data in some small areas

What’s next?
• User research:
o Increasing understanding of user needs and priorities
• Statistical Disclosure Control:
o Further assurance of SDC methods
o Refining disclosure control parameters
• Next phase of system development

Hands On Session
• Flexible Dissemination System Prototype
o Test out the tool yourself on the laptops provided
o Try out a User Persona to access Census data
o Please complete our mini questionnaire afterwards
o Opportunity to provide feedback in a group discussion in 45 mins
• Please remember: It’s a prototype…..
o The data are artificial
o It’s demonstrative not representative
o The SDC methods and parameters are a work in progress
o Pass rates are illustrative not actual

Other Activities
• User Journey Activity
o Plot your own User Journey
o How would you expect to access, create and download your own
Census table?
• Statistical Disclosure Control Display
o Find out more about the methodology behind Flexible
Dissemination System

Enhanced Census Outputs
Administrative Data Census Team
Spring 2018

Enhanced Census Outputs are…
Census based outputs where census
and administrative data are linked at
record level to enable the production of
multivariate, small area outputs

How do Enhanced Census Outputs differ
from Research Outputs?
Research Outputs Enhanced Census Outputs
Base Statistical Population
Dataset
2011 Census (to test quality)
and 2021 Census
Priorities Replicating as many census
topics as possible
Replacing some census
questions and producing new
topics

ECO topics
Number of rooms
Income
• Intend to recommend number of bedrooms question
be asked on the 2021 Census
• Continue research into using VOA data (and
potentially other sources) for 2021 Census outputs on
number of rooms (subject to statistical quality of the
admin data)
• High user requirement
• Admin Data Census Research Outputs already
produced – methodology to be applied to ECOs
• Awaiting self-assessment data (expected later this year)

ECO topics
Size of property
• Eurostat requirement currently met using English
Housing Survey
• Current research involves looking at the size of property
variable in the VOA data
• May provide more relevant data on occupancy rating
(research ongoing)

Possible other topics to consider in
medium-long term
Improving existing census topics (opportunistic use
of existing data)
Using VOA data to provide more detailed
breakdown of property type
Improving qualifications
statistics using data from
DfE, HESA etc

Next Steps
• To continue research and development for ECOs into:
1. Number of Rooms
2. Income
3. Size of Property
• Understanding data sources and user needs(See ‘Upcoming
Events’ slide)
• Developing and testing the methods and processes
• Assessing statistical quality of Enhanced Census Outputs
against National Statistics requirements
• Harmonisation

Our questions to you…
• Is there anything more on these topics
that you want to know?
• Are there any surprises in what we’re
covering?
• Statistical quality vs. geography?
National vs. experimental statistics?

How you can respond…
• Consultation
• Email:
Admin.Data.Census.Project@ons.gsi.gov.uk
• Come and have a chat

Upcoming Events
• Conference: Integrated data - Combining
data to answer society's biggest questions
9th – 10th July 2018
University of Surrey
• Transforming Labour Market Statistics by
Integrating Survey and Non-Survey Data
17th May 2018
Amba Hotel Charing Cross, London

2021 Census Outputs and Dissemination:
Closing
Spring 2018

2021 Census Outputs – What next?
2018
• Initial view on 2021 Census Output Content Design
2019
• Census Rehearsal
2020
• Finalise plans for 2021 Census outputs
2021
2022
• Begin publishing outputs
• Census Day

Questions
Please get in touch with any further feedback or questions:

2021
Microdata products
Census 2021 | Outputs and Dissemination team | census.outputs@ons.gov.uk
What are census microdata?• Samples of anonymous unit-
record data from both
individuals and households
• Variables and derived
variables created using
responses to census
questions
• Census microdata products
have been published since the
1991 Census
Successes and lessons in 2011:
Some users of our microdata:
2021: Priorities for microdata
• Repeat the successes of 2011 products
• Products more timely and accessible
• New variables to reflect new questions
• Update product design where necessary
• Review disclosure control methodology
• Identify if UK-wide products are
possible
• Assess the possible use of admin data
• Possibility of safeguarded household
file
2011 public-access file:
What went well:
• Most comprehensive products to date
• Nested sampling methodology across
files
• First ever public-access file produced
Lessons learned:
• Products need to be considered earlier
• Accessibility concerns must be
Other census microdata:
You can also access historical microdata:
• Similar products for past censuses
• Files made from 1981, 1971 and 1961
data
• Similar file types and access
2011 Microdata products:
How are we engaging with users?
• Public consultation with users
• Working group with users and census
offices of Scotland and Northern
Ireland
In 2011 we made three microdata
products, with different levels of detail
and security, which we plan to replicate
in 2021:
Advantages over aggregate
data:• More complexity
• More flexibility
• More variables
• Comparability
across censuses
• All data in one file
• More multivariates
• Better represents
small populations
• Useful in linkage
1% sample, available to everyone online
Public-access
file:
5% sample, available with registration
Safeguarded
files:
10% sample, available in secure settings
Secure files:
First Name Last Name DOB County Occupation Ethnicity
John Smith 07/07/1993 Hampshire Researcher White British
Sensitive input (census responses)
A random 1% sample of records is selected, identifiable
information is removed, disclosure control methods are
applied, derived variables are added, all variables are
coded, and a codebook is created to help users interpret
data.
caseno age region occg ethnicityew fmspuk11
####### 24 10 21 01 2
Microdata output (safeguarded file)
(Removed sensitive
data)
(New
variable)

Click to edit Master title style
55
What are origin-destination data?
· Provide information relating to the flows
between two locations, and the characteristics
(gender, age, ethnic group) of the individuals
who make these journeys
· Derived from several census questions, relating
to place of current residence, place of residence
one year prior to census day, main place of
work and second residence if applicable
Diagram showing the flows between location of usual residence and place of work using 2011
origin-destination data for Portsmouth. Image available from
https://www.nomisweb.co.uk/census/2011/WU03UK/chart/1132462339
Types of origin-destination data
There are two main types of origin-destination
data:
1) Residential migration in the year before the
census (both internally and from abroad)
2) Travel to work by those (aged 16 and over) in
employment the week before the census and
their mode of transport. In 2011, this was
available for both main and second residence, if a
respondent resides there for more than 30 days a
year
Why are they important?
Census information on migration and commuting patterns means we can
assess:
• movement patterns in the population
• how and if the characteristics (age, gender, ethnicity and socio-economic
status) of these populations are changing
These data are of vital importance to local and central government in order to
strategically plan infrastructure for health, education, transport and housing
based on population need.
3 ways to access 2011 data
What are our plans for 2021?
We’re currently developing our plans for the 2021
Census origin-destination data. We’re doing this by:
· assessing the most appropriate access
arrangements with consideration of confidentiality
· assessing the number of tables to be produced and
the variable groupings in tables
· assessing Statistical Disclosure Control methods in
order to make more data available publicly
· researching what went well in 2011 and what
improvements are needed for 2021
· establishing a working group with external
stakeholders to advise on the creation and
dissemination of origin-destination data
For 2021, our key aim is to ensure that origin-
destination data are available within two years of
census day (sooner than 2011).
If you want more information or have any
suggestions please contact us at
census.outputs@ons.gov.uk.
Public
Availability:
- Available under “Open
Government License”
- Available via the NOMIS
website
Users:
Local authorities,
transport planners,
academics, students,
general public and local
interest/community
groups
Key facts:
- There were 20 publicly
available tables
- Since 2011, public
origin-destination tables
have been downloaded
138,000 times
Safeguarded
Availability:
- Only available to data
analysts under certain
terms and conditions
- Safeguarded tables were
made available via the UK
Data Service
Users:
Central and local
government, researchers,
academics and higher
level students
Key facts:
- Since 2011,
safeguarded tables have
been downloaded 3,900
times
Secure
Availability:
- Tables only available via
the ONS Secure Research
Service
- The secure data provide
multivariate flows at low
levels of geography
Users:
Researchers engaged in
large-scale social research
Researchers must be
completing research
deemed for the “public
good”
Key facts:
-Users must become
“Approved Researchers”
before gaining access to
the data
-Since 2011, there have
been 24 unique projects
using origin-destination
data
Image showing travel to work flows using census origin-destination. Blue lines represent
flows coming in and red lines show flows out from the selected location, to work
elsewhere. Image available from http://blog.datashine.org.uk/2014/07/datashine-travel-
to-work-flows/
Origin-destination data

National Statistics for Census 2021
The Outputs and Dissemination team is working in collaboration with teams throughout ONS who are involved in delivering
a successful census. Our aim is to ensure we successfully retain the National Statistics accreditation for the 2021 Census.
Innovations such as the development of new questions, the Statistical Disclosure Control methodology and the flexible
dissemination system will be of particular interest to the awarding body, the Office for Statistics Regulation. We’ll provide
testable evidence to demonstrate that we meet the Code of Practice for Statistics.
The Code of Practice is… a framework for producers of official statistics with the detailed practices they must commit to
when producing and releasing official statistics. The Code is based on three pillars and the following principles:
TRUSTWORTHINESS
Confidence in the people
and organisations that
produce statistics and data
QUALITY
Data and methods that
produce assured statistics
VALUE
Statistics that support
society’s needs for
information
Suitable data sources
Sound methods
Assured quality
Relevance to users
Accessibility
Clarity and insight
Innovation and improvement
Efficiency and proportionality
Honesty and integrity
Independent decision making and
leadership
Orderly release
Transparent processes and management
Professional capability
Data governance
The interests of users of statistics sits at the heart of the Code and we’re committed to involving users in the development of
our outputs. Help us to deliver census outputs by informing us how you use our data and take part in the consultation.

Targeted Record Swapping
Disclosure Checks
Cell Key Perturbation
Impact
Pairs of similar households from different geographical locations are swapped
Key features:
• This was the main source of protection used in the 2011 Census and will be the main source of protection for 2021
• Risky households are more likely to be swapped than non-risky households but all households have a chance of being
swapped
• Households are only swapped with other households of the same size so the number of persons and households for
each area are preserved
• Households are swapped within Local Authorities, however in rare cases, if a household has very unusual
characteristics then it could be swapped with a match in a nearby Local Authority. There are no households in Cornwall
swapped to Birmingham for example
Small inconsistencies can occur from the cell key method
when cells are constructed or aggregated in different
ways
Small changes are made to cells consistently to protect against
differencing
The criteria determining what level of detail is safe to
publish
Key features:
• The checks will be applied automatically speeding up the time between census day and publication as there will be
no need for ONS staff to assess every table as was the case in 2011
• The checks will be applied to each geography individually allowing more detail to be published for the areas that
pass the checks, unlike in 2011 where only the minimum amount of detail that passed for the whole country could be
published
• Key tables, for example univariates, will be published for all geographic areas
Key features:
• This method is adapted from the method originally developed by Australian Bureau of Statistics for protecting
their census tables
• Perturbation is applied consistently so that cells will always be perturbed in the same way; the same cell in a
different table will always have the same value
• To allow small cells to appear in census tables, zero value cells are also perturbed using a similar method which
will result in a consistent perturbation of zeros
• The method was originally developed to protect against disclosure from differencing when similar tables are
compared
Key features:
• The cell key method will be applied as a “light touch” so inconsistencies that occur are likely to be small
• Larger tables and tables that contain a large number of small cells will be more affected
What is Statistical
Disclosure Control (SDC)?
The application of methods to
protect individuals,
households and their
characteristics from
identification in published
tables (and microdata).
Why do we need SDC?
The Office for National
Statistics (ONS) has legal and
ethical obligations to protect
the data that we collect.
Failure to do so could result in
reduced response rates
affecting the quality of the
data.
In order to protect the data
and include small cells in the
published tables, we need to
modify the tables or
underlying microdata by
adding a sufficient layer of
uncertainty as to whether a
disclosure is real or not.
Assign each record a random number (rkey) For each cell, sum rkey and apply a function to get a
cell key
Use a look up table to get a perturbation value Apply the perturbation value to
the cell
Record rkey
r1 54
r2 4
r3 93
…
rN 26
Record rkey
r2 4
r4 61
r56 7
r72 90
Sum = 162
e.g. take the last two digits →
ckey = 62
Age by
sex
Male Female
0-15 . .
16-24 . 4
25-34 . .
…
Age by
sex
Male Female
0-15 . .
16-24 . 5
25-34 . .
…
1 2 3 … 61 62 63 … 99
1 +1
2 +1 -1
3 +1
4 -1 +1
5 -1 -1
…
Cell
Key
C
e
l
l
V
a
l
u
e
The same marginal totals in different
tables
Marginal totals can be created by
summing over the other variables in the
table. If you create a table of variable x
by y and compare it with a similar table
of variable x by z, you may see
differences between the values in the
marginal total of variable x.
Variables that are grouped differently in
different tables
Perturbation is applied to each cell
independently and grouping categories in
different ways will result in different
record keys and different perturbation
values being applied. This can also affect
the zeros perturbation.
Aggregating smaller geographies into a
larger area
Tables at different levels of geography
are perturbed independently so if you
sum all the Output Area (OA) level tables
within a Middle Super Output Area
(MSOA), the values may not match the
values in the perturbed MSOA table.
Aggregated
OAs
T
o
t
a
l
+
3
T
o
t
a
l
-
3
T
o
t
a
l
-
4
T
o
t
a
l
+
2T
o
t
a
l
-
1
Perturbation
total = -3
MSOA table
T
o
t
a
l
+
2
Perturbation
total = +2
Difference
= 5
Five year age
groups
Ten year age
groups
Ag
e
10-
14
Ag
e
15-
19
+
0
+
1
Age
10-
19
-
1
Difference
= 2
Ag
e
0-4
Ag
e
5-9
+
1
+
0
Age
0-9
+
0
Difference
= 1
p
v
a
l
u
e
p
v
a
l
u
e
For each record in the sample, look in the
surrounding areas for a similar household of the
same size
3
Table: Pet ownership by weekly household
expenditure
Why is this table
not safe to
publish?
Identity disclosure
Lots of 1s in a
table could mean
that respondent
could be identified
Attribute
Disclosures
When all values in a
row fall into one
column, you can
learn something
new about a
respondent. For
example, you can
work out a
household’s
expenditure by
knowing which pet
they have
Swap the households4
Select a sample of households to swap with
risky households more likely to be selected
2Identify risky households, for example unique on
some characteristic
1
Difference
= 3
x x +1 x x
y .. .. +1 .. ..
y .. .. .. .. ..
y .. .. -1 .. ..
y .. .. .. .. ..
y .. .. +1 .. ..
x x -2 x x
z .. .. .. .. ..
z .. .. -1 .. ..
z .. .. .. .. ..
z .. .. -1 .. ..
z .. .. .. .. ..
Using the 2021
method:If this area is safe
then it will be
published
If this area is not
safe then it won’t
be published
Using the 2011
method:This area, although
safe, could not be
published…
… because this
area is too
disclosive to
publish
Output
Area 1 £0
- £499
£500
- £999
£1,000
- £1,499
£1,500+
Dog 4 40 11 3
Cat 2 34 5 2
Fish 3 15 2 0
Horse 0 2 3 1
Other 1 10 3 0
Mixed 0 5 2 2
None 5 137 18 0
Output
Area 2 £0
- £499
£500
- £999
£1,000
- £1,499
£1,500+
Dog 0 52 0 0
Cat 0 36 0 0
Fish 0 1 0 0
Horse 0 0 0 1
Other 0 1 0 0
Mixed 0 0 0 0
None 1 203 0 0
Statistical Disclosure Control team
SDC.Queries@ons.gov.uk
Flexible Table Builder: Statistical Disclosure
Control Proposed method for Census 2021
1 2
3 4
1 2 3

2021 Census Outputs and Dissemination: Introduction

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2021 Census Outputs and Dissemination: Introduction