Population Bases, Local Government
Users and the 2011 Census
Chris W Smith, Lucy Baker and Jacqui
Jones (Office for National Statistics)
Introduction
• Important to make the distinction between population
base at enumeration and population base at output
• Two choices of population base at enumeration:
– Usual Residence
– Population Present
• Usual Residence used in 2001 - what base, or bases,
should be used in 2011?
Past UK censuses
• In planning 2011
census, it is vital to:
– Evaluate advantages and
disadvantages of bases
used in the past
– Take note of why each
base was chosen.
• ‘Population present’
traditionally used by
census, at both
enumeration and
output, from 1801-1971
• 1931 Onwards: Some
statistics produced by
asking ‘usual address’
• 1981: Clear that users
needed more
information based on
‘usual residence’
• 2001: ‘Usual residence’
sole population base for
enumeration
1981 Census
• Two bases of enumeration: usual address, and
where individuals spent census night
• Three population counts:
– One of population present
– Two of usually resident:
• Census transfer method
• Present/absent method (lower count)
• Transfer method only transferred back to the
area of usual residence, so household analyses
did not include people away from usual
residence on census night.
1981 Census
• Some causes of under-counting:
– People wrongly left off census forms
– Enumerators classifying as absent a
household with someone present
• Causes of double counting:
– Misunderstandings by form-fillers
1991 Census
• Again, both usual residence and
population present used as enumeration
bases.
• 1981 counts considered to be too
complicated – attempts were made to
simplify counts:
– Transfer method not used
– Present/absent base was improved upon.
1991 Census
• Despite changes, people were still
being wrongly omitted. Problems
identified were:
– Confusing instructions on the census
questionnaire on who to include
– Wholly absent households not legally
obliged to complete a questionnaire
– Some people who were away from their
usual residence filled in two
questionnaires.
2001 Census
• Data collected for the first time solely on a
usually resident basis
• Only one count produced, adjusted for
underenumeration
• No substantive information collected from
visitors
• Disadvantages:
– Respondents need a very clear understanding of
what ‘usual residence’ is
– Not everyone would feel that they have a ‘usual
residence’.
International census taking
• Most other census-taking countries use
usual residence as base for output, but
there is some variation in the
enumeration base used:
– Australia and New Zealand enumerate on
a de facto basis (visitors are included)
– Canada and the USA enumerate on a
usually resident basis (visitors are not
included)
Changes in society
• We need to recognise that society is changing:
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More diverse employment patterns
More weekly commuting
More dissolved households/marriages
Children ‘shared’ between parents
Pensioners spending part of the year abroad
– What does ‘usual residence’ mean to different
individuals?
– What really constitutes a household?
– What data is needed for planning service areas with
large daily fluctuations, such as commuter areas?
Changes in society
• Definitions need to be relevant to contemporary
society:
– Household size is falling
– Census vital in providing accurate and comprehensive data
on old people
– Effects of EU enlargement may have an as yet unknown
effect on population structure as migration increases and the
workforce becomes even more mobile
• Definitions of usual residence must include
alternative patterns of living without compromising
the majority’s understanding
• Definitions must be as simple as possible.
Single or multiple bases at
enumeration?
• Population present as sole base at enumeration has
some disadvantages:
– Difficult in collecting full household structure information
– Visitors in England and Wales would need to be transferred;
this is technically difficult
• Population present and usual residence could both
be used at enumeration:
– Comparisons can give a better understanding of more
transient populations
– Population structure is very diverse – those who do not feel
they fit into ‘usual residence’ may not fill in a form
Single or multiple bases at
enumeration?
• With population present, the timing of the
census becomes an important factor: different
populations will be counted if census day falls
on a weekday rather than a weekend; altering
the time of day that enumeration takes places
(e.g. midnight or midday) will also have an
effect on the population captured
• Disadvantages of multiple population bases:
– Loss of simplicity to respondents
– Increase in burden on respondents who are away
from their usual residence
– Is there any actual need for a count of population
present?
Multiple population bases at output
• Usually resident population is important, but
does not always produce the most relevant
counts.
– Most commonly asked for bases are:
• Individuals usually resident – population usually resident
• Households usually resident – population usually resident in
private households
– Bases less frequently asked for include:
• Population present – numbers present during census night
• Working population – numbers present that are working in an
area
• Daytime population – numbers present during daytime hours
– Demands for counts based on ‘usually resident’ outweigh
any other
– Persons present counts are commonly requested, often to
be used as comparator for the usual residence data rather
than as a base in its own right.
Multiple population bases at output
– The working population might be an
approximation of the daytime population: in
the 2001 census respondents were asked
for their workplace address (though
obviously not all respondents will be at
work during daytime hours, but workplace
address may give a good enough estimate
of the daytime population).
Multiple population bases at output
• Other bases will also be considered for 2011:
– Temporarily resident (such as weekday and
weekend population)
– Those living in institutions (such as university halls
of residence, prisons or care homes)
– Legal populations (such as those eligible to vote in
an area)
– Populations for whom specific services are
required
• Some bases may be better conveyed by
surveys or administrative sources (e.g. The
Labour Force Survey)
Multiple population bases at
output
• Drawbacks to producing data on many
different population bases:
– Response rate can be affected by complex
questioning
– Address questions take up a lot of space on the
census form.
– Thus the “trade-off” between response rates and
information gathered will be critical in any decision
on which population base(s) the census will use.
Conclusions
• The choice of enumeration base for the
2011 census is complex
• ONS need to ensure that user needs
can be met with the chosen base or
bases – a consultation document was
recently produced
• Testing and research will allow informed
decisions to be made
• The 2011 Census should ensure high
coverage, and produce statistics that
are accurate and relevant.
ONS Population Definitions Working
Group: Convened September 2004
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Seven LA representatives
Four Central Government representatives
Two Academic representatives
Three ONS representatives
Towards a clearer view of population bases
for the 2011 census?
• Usually resident base is strongly favoured
• Population present is too vague to provide
meaningful statistics
• Population present would produce a result that was a
chance occurrence on a particular day
• A clear set of rules is required to define the usually
resident population – for the armed forces, students
and those with more than one address
• Close consultation with users can identify every
possible multi-address situation; the working group
will address this issue
• This consultation is now underway; additionally
comments from other interested parties are
welcomed.