2.2 SELECTED SAMPLES AND FINAL SAMPLES
SAMPLE DESIGN
The samples were 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 2.8 'Reliability of estimates').
The SIH sample was designed in conjunction with the HES. In the combined sample, some dwellings were selected to complete both the SIH questionnaire and the HES questionnaire, while other dwellings were selected to complete the SIH questionnaire only. Dwellings were selected through a stratified, multistage cluster design from the private dwelling framework of the ABS Population Survey Master Sample. Selections were distributed randomly across a twelve month enumeration period so that the survey results are representative of income and expenditure patterns across the year.
SELECTED DWELLINGS, SAMPLE LOSS AND SELECTED HOUSEHOLDS
In 2003-04, 16,554 dwellings were initially selected for the combined sample. When field work commenced some dwellings selected for inclusion in the HES and SIH samples 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 surveys; 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. dwellings occupied by foreign diplomats and their dependants); or
- visitors.
In 2003-04 sample loss was 2,067 dwellings, 12.5% of the initially 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. In 2003-04, a separate household was created for each such group of residents. In 2003-04, 51 selected dwellings were split into 2 households, 2 into 3, and 1 into 4.
The net result of these activities was that 14,545 households were approached to complete the HES and/or SIH.
RESPONDING HOUSEHOLDS AND FINAL SAMPLE
Households selected for inclusion in the surveys can be categorised as responding or non-responding households. Responding households are either fully responding or partially responding. In the HES and 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.
The table 2.2.1 shows the differences between the number of households selected for inclusion in the surveys and the number of responding households included in the final samples.
Table 2.2.1 Selected and responding households |
| |
| | Households approached | Non-response | Final sample | |
| |
HES sample (ie included in HES and SIH) | 9 753 | 2 796 | 6 957 | |
SIH sample | | | | |
| -included in HES and SIH | 9 753 | 2 425 | 7 328 | |
| -included in SIH only | 4 792 | 759 | 4 033 | |
| -Total | 14 545 | 3 184 | 11 361 | |
| |
Of the 9,753 households initially selected for inclusion in both the HES and the SIH, 6,957 (71%) responded with sufficient information to be included in the final HES and SIH samples and an additional 371 responded with sufficient information to be included in the final SIH sample but not the final HES sample. Of the 4,792 households initially selected for inclusion in the SIH only, 4,033 (84%) responded with sufficient information to be included in the final SIH sample. In aggregate, 11,361 households were included in the final SIH sample, representing an overall response rate of 78%.
Tables 2.2.2 and 2.2.3 show the distribution of the final samples between states and territories and between capital cities and the balance of state.
Table 2.2.2 FINAL NUMBER OF HOUSEHOLDS IN HES AND SIH SAMPLES |
| |
| Capital City | Balance of state | Total | |
| HES | SIH | HES | SIH | HES | SIH | |
| no. | no. | no. | no. | no. | no. | |
| |
NSW | 1 199 | 1 537 | 545 | 1 093 | 1 744 | 2 630 | |
Vic. | 1 087 | 1 690 | 445 | 696 | 1 532 | 2 386 | |
Qld | 579 | 845 | 308 | 1 151 | 887 | 1 996 | |
SA | 581 | 890 | 283 | 367 | 864 | 1 257 | |
WA | 475 | 950 | 254 | 490 | 729 | 1 440 | |
Tas. | 416 | 423 | 139 | 400 | 555 | 823 | |
NT | 301 | 335 | 76 | 87 | 377 | 422 | |
ACT | 269 | 407 | . . | . . | 269 | 407 | |
Aust. | 4 907 | 7 077 | 2 050 | 4 284 | 6 957 | 11 361 | |
| |
. . not applicable |
Table 2.2.3 FINAL NUMBER OF PERSONS IN SIH SAMPLE(a) |
| |
| CAPITAL CITY | BALANCE OF STATE | TOTAL | |
| no. | no. | no. | |
| |
NSW | 3 131 | 2 117 | 5 248 | |
Vic. | 3 474 | 1 338 | 4 812 | |
Qld | 1 607 | 2 236 | 3 843 | |
SA | 1 713 | 701 | 2 414 | |
WA | 1 909 | 929 | 2 838 | |
Tas. | 811 | 739 | 1 550 | |
NT | 666 | 161 | 827 | |
ACT | 783 | . . | 783 | |
Aust. | 14 094 | 8 221 | 22 315 | |
| |
. . not applicable |
(a) Number of persons aged 15 years and above |