Sampling and recruitment methodology for a national eye health survey of Indigenous Australians

To review the process of sample selection and highlight the methodological difficulties encountered during a nationwide survey of Indigenous Australians, to determine the prevalence and causes of vision impairment and evaluate access to and utilisation of eye care services.

Using a multi-stage, random cluster sampling methodology, 30 geographic areas stratified by remoteness, were selected to provide a representative population of approximately 3,000 Indigenous Australians aged 5-15 and 40 years and older, and a small non-Indigenous sample in selected remote areas. Recruitment was adapted to local conditions. The rapid assessment methodology included a questionnaire, tests of visual acuity, trachoma grading, frequency doubling perimetry and non-mydriatic fundus photography.

The number of people examined was 2883/3662 (78.7%) Indigenous and 136 (83.4%) non-Indigenous. The percentage of the expected population who were enumerated during the survey varied; discrepancies were largest in urban areas (34.5%) compared to very remote areas (97.1%).

The unexpected variation in predicted population numbers and participation rates could be explained in part by local circumstances, degree of urbanisation, interpretation of the definition of 'Indigenous' and time constraints.

For successful recruitment, a community-specific approach is essential, including collaboration with local organisations and liaison with health workers of each gender.