The index of multiple deprivation 2000 access domain: a useful indicator for public health?

The access domain of the UK index of multiple deprivation (IMD) 2000 was designed to identify populations in small areas with poor geographical access to certain local key services. The measure is a composite of straight line distances to post offices, large food shops, primary schools and general practice surgeries for population sub-groups. Using the region of East Anglia as a case study area, this research evaluated the utility of the IMD2000 as an indicator of access to primary care. IMD2000 access scores for electoral wards were compared with a range of more detailed indicators of travel times and bus availability for visiting a general practitioner generated in a geographical information system (GIS). A range of easy-to-calculate surrogate variables was developed and tested as possible candidates to improve the explanatory power of the IMD2000 access score. The access domain was negatively correlated with the other five deprivation domains that comprise the overall index, suggesting that access should not be combined with the other measures of deprivation into a composite single score. The access domain was also found to predict access to primary care only with moderate accuracy. Two additional indicators of accessibility calculated in a GIS (road kilometres per thousand population and the presence of a major road in each ward) were found to add slightly to the power of the index. The predictive power of the index was best in urban areas, although it is in rural areas that access to primary care is a more important public health issue. The IMD2000 should be therefore used with caution as a measure of health service accessibility in rural areas.