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Future ABS housing surveys
The AHS was last conducted in 1999, with significant user-funding provided by the Commonwealth Departments of Family and Community Services, the Commonwealth Department of Industry, Science and Resources, the 6 state housing authorities and Australian Capital Territory Housing. The 1999 AHS incorporated a significant supplementary sample to provide estimates for the housing circumstances of Aboriginal and Torres Strait Islander Australians (excluding those living in sparsely settled or remote areas of Australia).
A 1998-99 review of the ABS household survey program concluded that the content of the 1999 AHS was already largely covered in other ABS surveys and that it would be more cost effective to collect the required additional information in existing survey vehicles. The two main topic areas not covered by other surveys were physical information about the dwelling and information about housing mobility. These areas will be covered by a housing supplement to the 2007-08 Survey of Income and Housing.
APPENDIX 2 SAMPLING VARIABILITY
The estimates in this publication are based on information obtained from the occupants of a sample of dwellings. Therefore, the estimates are subject to sampling variability and may differ from the figures that would have been produced if information had been collected for all dwellings. One measure of the likely difference is given by the standard error (SE), which indicates the extent to which an estimate might have varied because only a sample of dwellings was included. There are about two chances in three that the sample estimate will differ by less than one SE from the figure that would have been obtained if all dwellings had been included, and about 19 chances in 20 that the difference will be less than two SEs. Another measure of the likely difference is the relative standard error (RSE), which is obtained by expressing the SE as a percentage of the estimate.
For estimates of population sizes, the size of the SE generally increases with the level of the estimate, so that the larger the estimate the larger the SE. However, the larger the sampling estimate the smaller the SE in percentage terms (RSE). Thus, larger sample estimates will be relatively more reliable than smaller estimates.
In the tables in this publication, estimates with high RSEs, particularly those over 25% should be used with caution. Each table containing numerical data also contains the RSEs for that data.
RSEs OF COMPARATIVE ESTIMATES
Proportions and percentages
Proportions and percentages, which are formed from the ratio of two estimates, are also subject to sampling errors. The size of the error depends on the accuracy of both the numerator and the denominator. For proportions where the denominator is an estimate of the number of households in a grouping and the numerator is the number of households in a sub-group of the denominator group, the formula for the RSE is given by
Differences between estimates
The difference between survey estimates is also subject to sampling variability. An approximate SE of the difference between two estimates (x-y) may be calculated by the formula:
This approximation can generally be used whenever the estimates come from different samples, such as two estimates from different years or two estimates for two non-intersecting subpopulations in the one year. If the estimates come from two populations, one of which is a subpopulation of the other, the standard error is likely to be lower than that derived from this approximation, but there is no straightforward way of estimating how much lower.
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