2940.0 - Census of Population and Housing - Details of Undercount, 2011  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 21/06/2012   
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For Census and PES purposes, scope refers to the group of people about which information is required. Usually a set of rules is applied to determine whether a selected person is within this population of interest.

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. However, for practical reasons there were a number of areas, dwellings and people outside the scope of the 2011 PES. Some people who were selected in the PES sample did not meet these scope rules, however were identified during the PES interview and excluded from the PES population. Of the people present in Australia at the time of the PES, the following were not included:

  • overseas visitors who were not in Australia on 9 August 2011 (Census night);
  • foreign diplomats and their families;
  • people in non-private dwellings (NPDs) such as hotels, motels, hospitals and other institutions;
  • people who were not in dwellings (as the sample selected in the PES is based on a selection of dwellings);
  • babies born after 9 August 2011; and
  • people in Cocos (Keeling) Islands, Christmas Island, Australian Antarctic Territory and Jervis Bay Territory.

The PES does not obtain information about people who died between Census and PES. However, it does obtain information about Australian residents who were overseas during the PES enumeration period and who departed after the Census, provided these people usually live with people remaining in Australia in a private dwelling selected in the PES.

In practice, the PES is used to produce estimates for the full Census scope, even though its actual scope and coverage is somewhat less.

Remote areas and discrete Indigenous communities

The 2011 PES included remote areas and discrete Indigenous communities. These areas and communities were first included in the 2006 PES. Prior to this, these were excluded from PES coverage due to operational difficulties around enumeration and around ensuring the independence of the PES from the Census, given the important role of local facilitators in these areas and communities.

Inclusion of these remote areas and discrete Indigenous communities in 2011 ensured a more complete geographic coverage of the PES. In 2011, the risk to statistical independence in these areas and communities was effectively managed through interviewer training and field staff procedures. No PES interviewer collected for Census in the same area where they were enumerating for PES.

Non-private dwellings

The 2011 PES sample excluded people living in non-private dwellings, as has been the case in previous PES cycles. Non-private dwellings are establishments which provide predominantly short-term accommodation for communal or group living, and often provide common eating facilities. They include:
  • hotels;
  • motels;
  • hostels;
  • hospitals;
  • religious institutions providing accommodation;
  • educational institutions providing accommodation;
  • prisons;
  • boarding houses; and
  • short-stay caravan parks.

Non-private dwellings each comprise a number of dwelling units. For further information on the operational difficulties around effectively enumerating non-private dwellings for the PES, see Information Paper: Measuring Net Undercount in the 2011 Population Census, Australia (cat. no. 2940.0.55.001).


Coverage refers to a set of rules designed to give each person in the PES sample, who is also in scope, a single chance of selection in the survey. These rules are implemented by associating each person with a single dwelling through a series of questions in the PES interview, such as where each person usually lives and whether they (or anyone else) are staying at their usual residence on 'PES night'.

An example of the need for coverage rules is for a visitor staying at a dwelling selected in the PES. If they report that someone else is staying at their usual residence during PES enumeration, then there is a possibility that this visitor could be included twice in the PES, once at their usual residence by another person, and again at their current location. Regardless of the low probability of both dwellings being selected in the PES, this respondent will be deemed out of scope as there is a chance that they would otherwise be included more than once in the PES.


Field procedures

Various field strategies were devised for the enumeration of the 2011 PES. Where possible, standard procedures were used when enumerating private dwellings and in discrete Indigenous communities. However, in some cases it was necessary to modify these procedures, particularly in discrete Indigenous communities, to account for language and cultural issues, while still ensuring the underlying concepts remained the same across both sample components.

The collection methodology of the PES was tested in a formal dress rehearsal, held after the Census dress rehearsal in August 2010. This allowed PES collection procedures to be tested. Efficiencies identified as a result of the dress rehearsal were then implemented before 2011 PES enumeration.

Mainstream sample

Specially trained PES interviewers collected data through face-to-face interviews which started around three weeks after Census night. Some telephone interviews were conducted by office staff, where the respondent made contact with the office and asked to complete the interview on the spot. All mainstream dwellings were enumerated using Computer Assisted Interviewing (CAI). Interviews were conducted with any responsible adult of the household who was asked to respond on behalf of all household members.

This collection methodology differed to the way Census collected its information, where most forms were self-completed.

A major advantage of interviewer-administered questionnaires is that people can be provided with assistance if they are uncertain about the meaning of questions, and help is also given to ensure no questions are left unanswered.

To ensure a high response rate was achieved, the number of repeat visits made to non-contact dwellings was twice that of most other ABS household surveys.

Discrete Indigenous communities sample

Interviews in discrete Indigenous communities were conducted by specially trained ABS interviewers with the assistance of facilitators recruited from within the selected community. The facilitator assisted in establishing rapport with respondents, helped identify residents of the selected households, and provided interpretation when needed.

To preserve the independence of the Census and the PES, every effort was made to recruit facilitators who were not involved in Census collection. Where this was not possible, PES interviewers ensured facilitators had only a limited role in the PES interview and provided assistance only where necessary, such as with language interpretation. In some communities it was acceptable to enumerate without the help of a facilitator, but generally they played an important role in being able to effectively enumerate in the communities.

The primary collection method in discrete Indigenous communities was also face-to-face interviewing using a CAI instrument. However, for practical reasons, a pen-and-paper interview (PAPI) questionnaire was also available, which provided interviewers with flexibility in situations where it was difficult to use a computer. Where PAPI forms were used, interviewers later transcribed the information into the CAI instrument, generally while still in the field.

Census follow-up

In each Census there are always dwellings for which Census forms have not been returned within the required time frame. For this reason, intensive Census follow-up procedures were employed at the end of the Census collection period.

Census follow-up periods for both the mainstream areas and discrete Indigenous communities were closely monitored by PES staff to ensure that the risk of overlap between the Census and PES was effectively managed. The timing of PES enumeration was based around the dates of Census follow-up, and was designed to start as soon as possible after Census activities had concluded in each area.

PES enumeration in mainstream areas began on Sunday 4 September 2011 and continued until Monday 3 October 2011. Almost all Census follow-up activities had been completed by the time PES enumeration began, although PES enumeration was delayed by a few days in a small number of areas to avoid overlap with final Census follow-up.

PES enumeration in discrete Indigenous communities began in early September 2011 and was completed by early October 2011. As PES enumeration of discrete Indigenous communities had a staggered start date (based on when Census field operations in each community were complete), there was no overlap between PES enumeration and Census collection in the selected communities.

As in previous PES cycles, special procedures were implemented for Census forms received after the start of the 2011 PES field work. These procedures ensured the independence of the Census and the PES was maintained, as receiving the PES primary approach letter or the arrival of a PES interviewer may have prompted the return of uncollected Census forms.

Any Census form received after the start of PES field work was flagged as a 'late return'. The treatment of late returns is explained in the Identifying Census late returns Technical Note (in Explanatory Notes).


Private dwelling questionnaire

The PES questionnaire collected personal details (name, sex, date of birth, age, relationship in household, marital status, country of birth and Indigenous status) to facilitate the matching of PES person records to Census person records during processing, and to allow accurate undercount estimates to be generated for age and sex categories, and Indigenous status.

The PES also asked respondents:
  • whether they were included on a Census form (and if so, where);
  • whether they could have been included on a Census form at other addresses (and if so, where); and
  • where they stayed on Census night.

The different addresses collected in the PES were used to search Census records to determine the number of times each PES respondent was included in the Census. Visitors to households included in the PES were also asked for their address of usual residence.

In addition to questions relating to Census night, the PES collected a small amount of information on dwelling tenure and structure.

Change to the collection of Indigenous status

The most significant change to the Private dwelling questionnaire was a change in how Indigenous status was collected.

In order to ensure that Indigenous status was effectively collected in the 2011 PES and that all Aboriginal and Torres Strait Islander persons were identified, the ABS removed a household 'screening' question that had been previously used in the PES. This meant that the Indigenous status question was collected for everyone in the dwelling, on a person by person basis. This aimed to reduce an assumed response bias in the previous questionnaire.

This represented a departure from the format of previous PES questionnaires, but was considered by the ABS to be a necessary departure based on trials of the change in the 2010 PES Dress Rehearsal. It was also well supported by a robust Interviewer training program and support materials, which reinforced the importance of collecting and recording Indigenous status correctly for all respondents.

This brought the Private dwelling questionnaire into alignment with the Discrete Indigenous Community questionnaire.

Discrete Indigenous community questionnaire

As in 2006, a number of questions in the mainstream PES questionnaire were not considered applicable to people living in discrete Indigenous communities and were adapted to ensure information was collected in the most culturally appropriate manner. For example, it is more common for Indigenous persons in a community to be known by more than one name. The tailored discrete Indigenous community questionnaire ensured that sufficient information was collected to effectively match persons, taking into account the potentially different nature of matching for people in discrete Indigenous communities.

A community-level questionnaire was also completed for each selected community with the help of the community contact or council officer. Information collected, such as whether a significant event occurred at the time of the Census (for example, a sports carnival), helped with respondent recall and assisted in the completion of parts of the individual questionnaires.


PES sample

The 2011 PES sample comprised two components; private dwellings (houses, flats, etc.) within the mainstream sample, and private dwellings within discrete Indigenous communities. As described earlier, non-private dwellings (hotels, motels, hospitals) were again excluded from the PES sample for operational reasons.

In total, approximately 35,000 dwellings were expected to respond to the PES, including around 500 dwellings from 28 discrete Indigenous communities. This was more than the 2006 PES sample, where approximately 32,000 dwellings were expected to respond, with 200 of these from 20 discrete Indigenous communities.

Focused sampling

In order to improve the estimates of Indigenous undercount, the 2011 PES increased the number of discrete Indigenous communities selected as well as the total number of dwellings selected within these communities. Also, since approximately three-quarters of the Indigenous population usually reside outside of discrete Indigenous communities (based on 2006 Census data), the number of selected dwellings in the mainstream sample was increased within areas identified as having a relatively high proportion of Indigenous persons.

These two methods were employed with the aim of being able to obtain a more accurate estimate of net undercount for Australia's Indigenous population by decreasing sampling error on the estimates.

For more information on the PES sample design, see the Explanatory Notes.

2011 Response Rates

After allowing for sample loss, the total number of fully responding dwellings (for both sample components) was almost 36,000. This represented a response rate of approximately 94% for the mainstream sample (the same rate as was achieved in 2006) and 96% for the discrete Indigenous communities (up from 91% in 2006).

The diagram below shows the number of dwellings in the two components of the PES sample for the main response types.

Diagram: 2011 Response Rates

The expected and actual dwelling selections for the 2011 PES Mainstream and ICF samples are shown in Tables 14 and 15 respectively.

14 DWELLINGS, PES sample - Expected and actual dwelling selections - Mainstream sample

Expected selections
Actual selections
Expected fully responding
Actual fully responding

New South Wales
8 967
9 504
7 618
7 805
7 614
8 039
6 450
6 727
7 608
7 858
6 394
6 468
South Australia
4 380
4 592
3 694
3 869
Western Australia
5 382
5 576
4 410
4 607
2 373
2 469
1 971
2 063
Northern Territory
2 923
2 975
2 460
2 466
Australian Capital Territory
1 564
1 538
1 349
1 368
40 790
42 551
34 346
35 373

15 DWELLINGS, PES sample - Expected and actual dwelling selections - ICF sample

Expected selections(a)
Actual selections
Expected fully responding
Actual fully responding

New South Wales
South Australia
Western Australia
Northern Territory
Australian Capital Territory

- nil or rounded to zero (including null cells)
(a) The number in the brackets refers to the number of discrete Indigenous communities from which the ICF dwellings were selected.