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2940.0 - Census of Population and Housing - Details of Undercount, Aug 2006  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 31/08/2007   
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1 The 2006 Census of Population and Housing was held on 8 August 2006. The objective of the Census was to measure the number and key characteristics of people in Australia on Census night, and the dwellings in which they live.

2 The Census attempts to count every person who spent Census night in Australia. This includes Australian residents in Antarctica and people in the territories of Jervis Bay, Cocos (Keeling) Islands and Christmas Island. The other Australian External Territories, Norfolk Island and minor islands such as Heard and McDonald Islands, are outside the scope of the Australian Census. Australian residents out of the country on Census night are also out of scope of the Census. The only people who spend Census night in Australia but are excluded from the Census are foreign diplomats and their families. People were counted where they stayed on Census night. This means that the Census was conducted on an 'actual location' or 'place of enumeration' basis.

3 Visitors to Australia are counted regardless of how long they have been in the country or how long they plan to stay. People outside Australia who are not required to undertake migration formalities, such as those on oil and gas rigs off the Australian coast, are included. People visiting Australia on Census night are included in the Census counts on a place of enumeration basis but not those on a place of usual residence basis.

4 All private dwellings, except diplomatic dwellings, are included in the Census, whether occupied or unoccupied. Caravans in caravan parks, manufactured homes in manufactured home estates and houseboats in marinas are counted only if occupied. Occupied non-private dwellings, such as hospitals, prisons, hotels, etc., are also included.

5 Details about the 2006 Census content, collection operations, confidentiality and privacy protection, processing and evaluation activities are contained in 2006 Census Nature and Content (cat no. 2008.0).


6 The scope of the Census is every person present in Australia on Census night (with the exception of foreign diplomats and their families). Ideally the PES would sample from all people who were or should have been counted in the Census - thus this set of people constitute the theoretical scope of the PES. For practical reasons there are a number of areas, dwellings and people excluded or not able to be covered by the PES. Of the people present in Australia at the time of the PES, the following are not included:

  • people in non-private dwellings such as hotels, motels, hospitals and other institutions
  • homeless people (as the sample selected in the PES is based on the selection of dwellings)
  • foreign diplomats and their families
  • overseas visitors who were not in Australia on 8 August 2006 (Census night)
  • babies born after 8 August 2006
  • people in Cocos (Keeling) Islands, Christmas Island, Australian Antarctic Territory, and Jervis Bay Territory.

7 The PES also does not obtain information about people who died between Census and the PES. However, it does obtain information about Australian residents who are overseas during the PES enumeration period and who departed some time in August, provided that they usually live with people remaining in Australia (in private dwellings).

8 The 2006 PES included remote areas and discrete Indigenous communities for the first time. Previous PESs have excluded these areas from the coverage of the survey due to operational reasons - mainly the additional cost and the need to use the same local contacts as Census, which was considered likely to compromise the independence of the PES. Inclusion of these communities in 2006 ensures that the geographic coverage of the PES is more complete than it has been in the past. In practice, the PES is used to produce estimates for the full Census scope, even though its actual coverage is somewhat less.

9 The PES interview process determines whether each person in the sample should have been counted in the Census, and a few of the categories in which they should have been counted (such as age, sex, Indigenous status, country of birth, region of usual residence, etc). The match and search process involves comparing dwellings and people enumerated in the PES with dwellings and people counted in the Census. The objective is to determine how many times each person in the PES sample was actually counted in the Census. PES output processing and estimation then combines and weights results from the match and search process to produce an estimate of the number of people who should have been counted in the Census.


10 Following the 2001 PES, a review of the PES estimation method was commissioned to develop an estimator for the PES that adjusts adequately for non-response and non-coverage in PES, and for miscounting in the Census.

11 The 2006 PES introduced a number of methodological improvements that allow more aspects of the Census to be appropriately measured. A side-effect of these changes is that the sampling error on the overall population estimates has increased, with previously unmeasured potential errors now being measured by the survey and included in adjustments.

12 Broadly speaking, PES estimation involves assigning a 'weight' to each selected PES dwelling and then to each person for whom a PES response was obtained. The PES estimate of the number of people who should have been counted in the Census is obtained as a weighted sum of the number of people in the PES sample who should have been counted in the Census.

13 Further details of PES estimation are in Appendix 3 of Census of Population and Housing - Undercount (cat. no. 2940.0) released on 5 June 2007. Technical details of the PES estimator were reported in Research Paper: An estimating equation approach to Census coverage adjustment (cat. no. 1351.0.55.019) released on 7 May 2007. Further descriptions of PES estimation can also be found in Information Paper: Measuring Net Undercount in the 2006 Population Census, Australia (cat. no. 2940.0.55.001) released on 7 May 2007.


Not-stated values

14 For Census purposes, age, sex, marital status and state of usual residence are imputed during Census processing where these items have been left blank, including where a whole person record has been imputed. Missing values for any other items remain 'not-stated' in the final version of Census counts.

Usual residence

15 The Australian Census counts people where they actually were on Census night, rather than where they usually live. There is, however, a need for data based on place of usual residence, and Census counts are available on this basis.

16 For usual residents of Australia, 'place of usual residence' for the 2006 Census is defined as the address at which a person has lived or intends to live for six months or more in 2006. While for most people their usual residence was the same as their actual location on Census night, some people spent Census night at a place other than where they usually lived. Thus, their 'place of enumeration' and their 'place of usual residence' were different.

17 Usual residents of Australia who are temporarily overseas on Census night are not included in Census counts on either a place of usual residence or place of enumeration basis. However, these people are accounted for in the estimated resident population of Australia (ERP). For information on the calculation of ERP, see the ABS publication Australian Demographic Statistics, December quarter 2006 (cat. no. 3101.0), released on 5 June 2007.

18 Estimates presented in this publication are on a place of usual residence basis.


19 The standard error (SE) on the PES estimate of the population in the non-contact sector has been calculated, and used in comparing the accuracy of the PES estimate with that of the unadjusted Census count for this sector. Analysis showed that the overall population estimates are considerably more accurate if the PES estimates are used for this sector rather than using the Census counts (which in this sector were mostly imputed). See Appendix for further information.

20 Net undercount estimates presented in this publication incorporate the PES estimates for the population in the non-contact sector.

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