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 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 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.

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 1981 Census

1991 Census Again, both usual residence and population present used as enumeration bases 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: 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

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? Single or multiple bases at enumeration?

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).

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 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.