Sampling methodology and site selection in the National Eye Health Survey: an Australian population-based prevalence study

Background To present the sampling methodology and selected testing sites of the National Eye Health Survey (NEHS); a cross-sectional population-based survey that aimed to determine the prevalence of vision impairment and blindness in Australia. Design Indigenous Australians aged 40 years and older and non-Indigenous Australians aged 50 years and older residing in all levels of geographic remoteness in Australia. Methods Using multi-stage, random-cluster sampling, 30 geographic areas were selected to provide a sample of 3000 non-Indigenous Australians and 1400 Indigenous Australians. Site selection involved; 1) Selecting Statistical Area-Level 2 (SA2) sites, stratified by remoteness; 2) Selecting Statistical Area-Level 1 (SA1) sites within SA2 sites to provide targeted samples; 3) Grouping of target SA1 sites with contiguous SA1s or replacing SA1s to provide sufficient samples. Participants were recruited using a door-to-door approach. Main outcome measures Sites selected and participants sampled in the National Eye Health Survey. Results Thirty sites were generated, including; 12 Major City, 6 Inner Regional, 6 Outer Regional, 4 Remote, and 2 Very Remote sites within 5 States and one Territory. 3098 non-Indigenous participants and 1738 Indigenous participants were recruited. Selection of SA1s overestimated the number of eligible residents in all sites. 20% (6/30) of SA1s were situated in non-residential bushland, while 26.67% (8/30) of SA1 populations had low eligibility or accessibility, requiring replacement with contiguous SA1s. Conclusions Representative samples of Indigenous and non-Indigenous Australians were selected, recruited and tested, providing the first national data on the prevalence of vision impairment and blindness in Australia.