1504.0 - Methodological News, Mar 2002  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 16/11/2001   
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SAMPLING STRATEGIES FOR INDIGENOUS HOUSEHOLD SURVEYS

The expanded ABS household survey program involves a series of regular large scale surveys of Aboriginal & Torres Strait Islander people. Upcoming surveys include the Indigenous Social Survey (ISS) and an Indigenous Supplement to the 2004 National Health Survey (NHSI). These surveys both aim to enumerate in excess of 10,000 Aboriginal & Torres Strait Islander people Australia wide, a significant proportion of the Indigenous population. The surveys present numerous challenges to all aspects of the survey process, particularly the development of appropriate sampling methodologies.

Remote Area Sampling

Approximately 20% of the Indigenous population reside in remote areas as defined in the Access/Remoteness Index for Australia (ARIA). These areas are in-scope of Indigenous household surveys, unlike most other ABS special social household surveys. Surveying in remote areas presents many problems, including

  • the very high cost of sending interviewers out to these areas;
  • protocol in approaching and conducting interviews in Indigenous communities; and
  • high levels of sample loss.

The 2001 NHSI saw the introduction of a list based frame into an ABS household survey which aimed to address the problems of sampling in remote areas. The frame was constructed from the 1999 ABS Community and Housing Infrastructure Needs Survey (CHINS), an administrative survey which collected information on housing and infrastructure from all Indigenous communities in Australia. In remote areas the Indigenous population resides largely in communities which are registered on CHINS. It was considered that the operational advantages of using a list based frame of CHINS communities far outweighed the impact of slight undercoverage. These advantages include:
  • more precise identification of where Indigenous people reside thereby avoiding high costs of screening large remote Collection Districts (CDs) (see non-remote sampling below);
  • appropriate formation of groups of associated communities, including smaller communities known as out-stations, into primary sampling units enabling interviews to be conducted more effectively with necessary permission and facilitation; and
  • a more cost effective sample.

As part of the Monthly Population Survey (MPS) redesign an Indigenous community stratum is being developed. This stratum will form the basis of the 2002 ISS and 2004 NHSI remote area samples. Although sample selection within this stratum will be CD based, the general sample selection concepts underpinning the 2001 NHSI sparse sampling methodology will be adopted. In particular, the 2001 CHINS will be crucial to the formation of groupings of CDs which will form the stratum frame. In addition, the use of a CD based frame will facilitate overlap control between the MPS and Indigenous special social surveys.

Non-Remote Area Sampling

Sampling Indigenous people in non-remote areas faces the daunting prospect of attempting to sample a rare population whose exact location is unknown. Sampling in non-remote areas involves a large search phase to initially identify households which contain Indigenous persons. It is this facet of the sampling methodology which is the most problematic. Based on 1996 Census figures, approximately 7% of the Indigenous population reside in CDs which contain only one Indigenous household. For some states this figure is much higher, (e.g. 28% in Victoria). Due to the significant numbers of Indigenous people residing in low Indigenous household density CDs it is not feasible to justify putting them out of scope of Indigenous surveys. This invariably leads to very high screening costs in order to identify and enumerate Indigenous households in these areas. For example, the 2001 NHSI non-remote sample aimed to select approximately 1065 fully responding Indigenous households. In order to achieve this, roughly 37,250 households were selected to be screened!

Adding to the problem is the mobility of the Indigenous population. For example, the 2001 NHSI sample design was based on Census figures which were 5 years out of date. This has resulted in lower than expected Indigenous sample takes in some areas, leading to a less efficient than expected sample.

For the upcoming 2002 ISS a number of methodologies are being investigated to develop more effective and efficient sampling methodologies for non-remote Indigenous surveys. These include:
  • stockpiling households from outgoing MPS rotation groups identified as containing Indigenous persons and then using these households to represent low Indigenous household density CDs;
  • putting low density Indigenous household CDs out of scope in some states;
  • introducing quota sampling for some strata in order to more effectively control the number of households screened;
  • sampling next door neighbours of identified Indigenous households in order to maximise the likelihood of obtaining expected Indigenous household sample size in the field.

Suggestions on alternative screening mechanisms are most welcome!

For more information please contact Alistair Rogers on (02) 6252 7334

Email: al.rogers@abs.gov.au