Measuring spatial accessibility to primary health care services: Utilising dynamic catchment sizes

• Highlights flaws of current use of single catchment size to the 2SFCA method.
• Trials use of ‘remoteness’ as break-point for dynamic catchment sizes.
• Develops a smoothing technique for catchment size transitions.
• Demonstrates initial successful application of dynamic catchment sizes in Australia.
• Enables use of 2SFCA method in national-level access models and health policy.

The two-step floating catchment area (2SFCA) method continues to be a popular measure of spatial accessibility, especially in relation to primary-level health care. Despite its popularity, most applications of the 2SFCA method are limited by the utilisation of only a single catchment size within a small geographic area. This limitation is significant to health policies which are mostly applied at the state or national scale. In this paper, a five-level dynamic catchment size was trialled within the 2SFCA method to all of Australia, with a population's remoteness used to delineate increasing catchment sizes. Initial trial results highlighted two perverse outcomes which were caused by sudden changes in catchment sizes between each level. Further refinement led to trialling an additional three-level catchment sub-type to the 2SFCA method, which created a smoother transition between remoteness levels. This study has demonstrated an effective approach to dynamically apply variable and more appropriate catchment sizes into different types of rural areas, which for the first time enables the 2SFCA method to be suitable for national-level access modelling and its potential application to health policy.