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A role for the ecological study in the developing world
Abstract
Retrospective case-control or prospective (followup) studies are important epidemiological tools and have provided useful infonnation on exposure disease associations. Prospective studies would be the ideal option, but m.any countries (Particularly in the developing world) do not have the necessary infrastructure to follow people up. Both retrospective and prospective studies are, however, som.etim. es conducted without due regard for their own lim.itations. These lim.itations are exacerbated when m.easures of exposure or disease are based on a single measurement and where the population under study is homogeneous with regard to exposure. The former is responsible for regression dilution bias and the latter for a lack of contrasts between exposure groups. Both factors would attenuate any relationship between exposure and disease. Ecological studies in epidemiology are weaker in design than case-control or prospective studies, but in some circumstances an ecological approach, which looks at the prevalence of an exposure or disorder in a number ofareas of varying disease rates, may offer some advantages.
