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The
One Number Census (ONC) project aims to integrate the 2001 Census
counts with the estimated underenumeration. First it will
provide a new base for the mid-year population estimates at the
Local Authority District (LAD) level, and second it will adjust the
Census database itself for the estimated undercount so that all
statistics add to 'One Number' - the national estimate of the
population.
The
primary source in estimating the underenumeration will be the Census
Coverage Survey (CCS). This has a notably different design
to the Census Validation Survey undertaken following the 1991
Census.
The
project derives its name from the intention to eliminate different
population counts so that all census outputs add to one number - the
national population estimate which has been adjusted for
underenumeration. Furthermore the mid-year population
estimates will be based on these ONC population estimates and there
will be transparency between them.
The
ONC Project considered the methodology separately for England and
Wales, Scotland and Northern Ireland. The high-level
methodology presented here is consistent throughout the UK.
Although there are some differences, these are mainly associated
with the design and practical aspects of the Census Coverage Survey
and the use of health board areas during the Quality Assurance
process in Scotland.
Why
is a One Number Census necessary?
The
primary aim of the Census is to provide a snapshot of the entire
population and thus provide high quality counts of the population
for small areas across the country. These statistics are used
for many important purposes. In particular, they provide a new
base for the mid-year population estimates which are used to help
distribute central government support to local authorities.
They also allow central and local government as well as health
authorities to plan health, education, transport and housing needs
for the years ahead.
Every
effort was made to ensure everyone was counted in 2001 and a
number of initiatives were introduced to maximise coverage.
However, no census is perfect and some people will have been missed.
Therefore, it is accepted practice throughout almost all similar
census-taking countries to assess the extent of any underenumeration,
usually by means of a post-enumeration survey.
How
will a One Number Census be achieved?
The
key ONC stages can be summarised as follows:
1. A Census Coverage Survey (CCS),
undertaken independently of the Census, was designed to establish
the coverage of the 2001 Census. For the CCS, the UK was
divided into one hundred and twelve areas (3 in Northern Ireland),
each with a population of about 500,000. These areas re known
as 'design' groups' and are made up of whole LADs or groups of
smaller LADs. The CCS took place in all of these design
groups.
2. The CCS records are matched with
those from the Census using a combination of automated and clerical
matching.
3. Design group populations, by age and
sex, are estimated using a combination of standard estimation
techniques are used to estimate Local Authority District populations
by age and sex.
4. Households and individuals estimated
to be missed by the Census are imputed to produce a fully adjusted
Census database.
5. All ONC population estimates are
quality assured using demographic analysis and aggregate level
administrative data.
Consultation
It
is important that users of census data have confidence in the 2001
Census figures produced by the One Number Census. Acceptance
was sought in a number of ways, including
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The
composition of the Census Advisory Group; |
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The
consultation process with census user groups; |
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A
Series A RSS paper (Brown et al, 1999); |
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Several
RSS seminars; |
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The
Census Consultation paper '2001 - A One Number Census'
(Available here in PDF
format); |
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The
Spring 1999 Consultation paper 'A Guide to the One Number
Census'. |
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A
workshop devoted to the One Number Census project in May 1998;
and |
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Special
workshops held in conjunction with Census Output Roadshows
during April/May 1999 and September/October 2001. |
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