ISSUES IN THE DESIGN AND INTERPRETATION OF STUDIES TO EVALUATE THE IMPACT OF COMMUNITY-BASED INTERVENTIONS

Increasingly, epidemiologists are faced with the need to evaluate the impact of an intervention that is delivered at the level of a communit y or cluster of individuals, rather than at the individual level. This has profound implications for the design and interpretation of a stud y to evaluate its impact. We start by discussing the issues arising in the extension of the randomized double-blind controlled trial methodo logy to the evaluation of interventions delivered to clusters of indiv iduals, or to whole communities, where the unit of randomization is a cluster of individuals rather than an individual. We then consider alt ernative approaches to design, discuss their relative strengths and we aknesses and present a framework of design options. Finally we propose a pragmatic approach to evaluation design in this setting. We believe that the answer lies in the judicious selection of different design e lements, combined in such a way that when the evidence from each is pr esented together, a clear picture of the impact of the intervention em erges. We illustrate this using an example from the recent literature.