The sample was designed to produce reliable estimates for broad aggregates for households resident in private dwellings aggregated for Australia, for each state and for the capital cities in each state and territory. More detailed estimates should be used with caution, especially for Tasmania, the Northern Territory and the Australian Capital Territory (see Section 2.8 'Reliability of estimates').
In the 2005-06 SIH, dwellings were selected through a stratified, multistage cluster design. Selections were distributed across a twelve month enumeration period so that the survey results would be representative of income patterns across the year. In the final quarter of enumeration, 25% of the selected dwellings were dropped from the sample. This reduced the overall number of dwellings selected to participate in the survey. This outcome will increase the standard error in the final quarter estimates and hence the standard error in the annualised estimates. This increase in standard error is included in the error estimation. The relative change in sample size across the enumeration quarters may also introduce some bias to the annualised estimates but this is expected to be much less than the standard error.
SELECTED DWELLINGS, SAMPLE LOSS AND SELECTED HOUSEHOLDS
In the 2005-06 SIH, 14,169 dwellings were selected for the sample. This excludes dwellings removed as part of the deselection mentioned above. When field work commenced some dwellings selected for inclusion in the SIH sample were found to have no possibility of delivering a survey response. Collectively these are referred to as sample loss, and are composed of the following groups:
- dwellings which are out of scope of the survey; under construction, demolished, or converted to non-private dwellings or non-dwellings
- private dwellings which:
- are vacant
- contain only:
- out of scope residents (e.g. dwelling occupied by foreign diplomats and their dependents): or
In 2005-06 sample loss was 1,915 dwellings, 13.5% of the selected sample.
Sometimes dwellings that have been selected for inclusion in a survey are found to comprise more than one actual dwelling because, for example, an additional residence such as a 'granny flat' has been added to the original dwelling. In such cases, each actual dwelling becomes a separate household. Occasionally the residents of a selected dwelling request that their details be provided separately from other dwelling residents, for privacy reasons. A separate household is created for each such group of residents. In 2005-06, 45 selected dwellings were split into 2 households, and 6 were split into 3.
The net result was that 12,311 households were approached to complete the SIH.
RESPONDING HOUSEHOLDS AND FINAL SAMPLE
Households selected for inclusion in the survey can be categorised as responding or non-responding households. Responding households are either fully responding or partially responding. In the SIH, information missing from partially responding households is imputed, as described in 2.4 'Data processing'.
Non-responding households include:
- households affected by death or illness of a household member
- households in which the significant person(s) in the household did not respond because they could not be contacted, had language problems or refused to participate
- households in which the significant person(s) did not respond to key questions.
In the 2005-06 SIH, households in which the significant person(s) responded to key questions but one or more other persons in the household aged 15 or over did not respond, were also treated as non-responding. In prior surveys these households were regarded as partially responding and responses for the missing persons were imputed.
Of the 12,311 households that were approached to complete the SIH, 9,961 (80.9%) were included as part of the final estimates. These 9,961 households comprised 19,212 persons aged 15 years old and over.
Table 2.2.1 shows the distribution of the final samples between states and territories and between capital cities and the balance of state.
TABLE 2.2.1 SIH FINAL SAMPLE, Number of households, 2005-06
Balance of State
|- nil or rounded to zero (including null cells) |
|(a) Number of persons aged 15 years and over |