Measuring spatial accessibility to services within indices of multiple deprivation: implications of applying an enhanced two-step floating catchment area (E2SFCA) approach

Approaches to calculating spatial accessibility within existing indices of multiple deprivation (IMD) methodologies are based on ‘traditional’ accessibility metrics and tend not to adopt more recent methodological enhancements. In particular, the last decade has seen a relatively large body of studies that have applied floating catchment area (FCA) methods that account for both service supply and potential demand interactions, mediated by the impact of distance, in a wide range of application areas. In this paper, we investigate potential implications of incorporating an FCA-based approach to measuring spatial accessibility within an existing IMD framework. Using the Welsh Index of Multiple Deprivation (WIMD) as a case study, FCA-derived accessibility scores were substituted for the existing approach used to calculate accessibility and a revised index was computed. The published methodologies used to construct the other ‘domains’ within the WIMD were followed and the implications for the overall deprivation measure were assessed. Statistical and visualisation tools revealed implications for both the access and overall IMD rankings, with sparsely populated (predominantly rural) areas tending to receive higher accessibility scores from FCA-based approaches than more densely populated (predominantly urban) areas. These areas in turn showed the greatest decline in ranking on the WIMD calculations following the application of FCA approaches. Potential reasons for such trends are posited before we conclude by drawing attention to the implications of adopting FCA-based approaches to calculate IMDs particularly for those policies designed to distribute funds or allocate resources to areas of need.