Publication Details

This report was originally published as Clark, RG, Comments on Sample Design for Proposed Australian Asthma Survey, Report prepared for the Woolcock Foundation, June 2006, 12p.


The proposed design for the Australian Asthma Survey involves: a phone or face-toface screening interview with approximately 20,000 responding adults, followed by an in-depth interview and objective testing of all asthmatics and 1/10th of nonasthmatics in the screen. This report elaborates on sample design options based on the aims and approaches in the Australian Asthma Survey Proposal. The main requirement affecting the sample design is the need for a relatively small number of objective testing centres to be able to service the whole sample. This report considered a number of options where the sample was clustered in only 25 Statistical Local Areas (SLAs), as well as other options. This will facilitate the objective testing with the penalty of a significant loss of precision for other statistics. The priority and operational process for objective testing should therefore be carefully thought through. In particular, the cost of objective testing should be estimated under different scenarios including selecting 50 SLAs rather than 25. There are a number of options for conducting the screening sample and subselection for the in-depth survey. These include screening all adults or just one adult in each household. One attractive option is to select one adult from each household for the screening interview, then to conduct the selection for the in-depth survey and if possible the in-depth survey interview as part of the same call. Other options exist which are more complex but which give good results with a smaller screening sample. The survey will also include children (at most one child per household) but this report focuses on the adult sample. The major issues to be considered in finalising the sample design are: • clustering of the sample to accommodate the objective testing process (in particular the number of SLAs); • method of conducting screening sample (one adult or all adults per household); • method of selection and conduct of in-depth survey, in particular can this be done by interviewers in one visit or phone call; • whether the screen and in-depth survey will be conducted by face to face or telephone interviewing. Other detailed issues will include: the stratification and selection method for SLAs; the number of CDs to select if face-to-face interviewing is used; the method of selecting CDs, the method of selecting households within CDs; weighting and variance estimation. Section 2 of this report summarises some relevant terms and concepts in comparing sample designs. Section 3 describes three alternative approaches for conducting the screen and in-depth surveys. Section 4 compares six alternative sample designs including alternative approaches to clustering the sample. Appendix 1 contains some detailed comments on the Proposal, Appendix 2 elaborates on one of the sample design options in more detail and Appendix 3 contains some comments on weighting.