Use of homogeneous social areas for ecological analyses. A study of accident rates in pre-school children

Abstract

Background: The results of ecological analyses are sensitive to the geographical areas used and census areas are not necessarily the most suitable units. This study compares the effects of using specially constructed areas with similar social characteristics rather than standard census areas as basic units in a small area ecological study. Methods: The study used ecological regression analyses of accident rates in pre-school children on social and demographic predictors using census enumeration districts, wards and specially constructed social areas as the units. The setting was the city of Norwich, UK and adjacent suburbs, consisting of 349 census enumeration districts nested within 30 wards or 21 social areas. Results: Analyses at different geographical scales produced similar estimates of the effects of material deprivation, presence of lone parent households and young population age structures on child accident rates, but the r² values varied considerably, the weakest relationships being found for enumeration districts and the best fitting for social areas. Adjusted r² values between log accident rates and material deprivation scores, for example, were 10.5% for enumeration districts, 52.7% for wards and 63.3% for social areas. Conclusions: Specially constructed areas were preferable to enumeration districts and wards as units for identifying ecological relationships between accident rates in pre-school children and social conditions. Homogeneous social areas are potentially useful units of analysis for ecological studies in epidemiology.