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INTRODUCTION

THE CENSUS OF POPULATION AND HOUSING

The Population Census is a valuable data source for estimating the size and geographic distribution of the Australian population, and for analysing the major demographic, social and economic characteristics of the population, particularly for small geographic regions and other small sub-populations. It provides statistics for decision-making by governments, businesses, community organisations and individuals.

A Census is conducted in Australia every five years by the Australian Bureau of Statistics (ABS). The most recent Census night was Tuesday 8 August 2006. Every person present in Australia on Census night, excluding foreign diplomats and their families, should have been included on a Census form at the place where they stayed.

The Australian Census counts people where they were on Census night. The ABS augments this Census count for net undercount and for Australian residents who were temporarily absent from Australia on Census night, and subtracts the count of overseas visitors temporarily in Australia and enumerated in the Census, to form a basis for the calculation of the Estimated Resident Population (ERP) of Australia on a place of usual residence basis.

Accurate ERPs are required for a wide range of uses, including the allocation to states and territories of seats in the Federal House of Representatives, the distribution of Commonwealth payments to states and territories, and demographic, social and economic studies.


NET UNDERCOUNT

Whenever a Census is undertaken, questions about the completeness and accuracy of the Census count invariably arise. In such a large and complex exercise, it is inevitable that some people will be missed and some will be included more than once. Some of the reasons why people may be missed (i.e. undercounted) include:

• they were travelling and were difficult to contact
• they mistakenly thought they were counted elsewhere
• there was insufficient space on the Census form in the household where they were staying and they did not obtain additional forms
• the person completing the form thought that, for example, young babies, the elderly or visitors should not be included
• they did not wish to be included due to concerns about the confidentiality of information or a more general reluctance to participate
• the dwelling they were in was missed because it was difficult to find (e.g. in a remote or non-residential area)
• the dwelling they were in was mistakenly classed as unoccupied.

• they were included on the Census form at the dwelling where they usually live, even though they stayed, and were counted, elsewhere on Census night
• they were overseas on Census night and so should not have been counted at all, but were included on the Census form at the dwelling where they usually live.

While every effort is made to eliminate these potential causes of error, some undercount and overcount will invariably occur in the Census. Usually more people are missed than overcounted in Australia, so the Census count of the population would be less than the true count. This difference is called net undercount. In this context, 'Census count' includes person records imputed for dwellings that were non-responding in the Census.

Rates of net undercount can vary significantly for different population groups depending on factors such as sex, age, ethnicity (including Indigenous status) and geographic location. The ABS obtains estimates of net undercount using information collected in a post-enumeration survey conducted immediately following the Census. Estimates of net undercount are used to:

• derive an estimate of the resident population for 30 June of the Census year (2006)
• provide users with an assessment of the completeness of Census counts, allowing them to take this into account when using Census information
• evaluate the effectiveness of Census collection procedures so that improvements can be made for future Censuses.

Contact Merilyn Henden on (02) 6252 5489 or email <merilyn.henden@abs.gov.au> for further information.