Complexity, evaluation and the effectiveness of community-based interventions to reduce health inequalities.

Reducing health inequalities has been part of the New Zealand government's agenda since the early 1990s. As a result, interventions have been implemented nationally with the explicit goal of reducing health inequalities. This paper describes findings from a comparative case study of two community-based interventions - carried out in different New Zealand communities. Complexity theory was used as an analytic tool to examine the case data, and provided a systematic way in which to explore 'local' issues by taking a 'whole system' perspective. The findings showed that two important influences on the successful implementation of the interventions were the existence and capacity of local organisations and their relationships with government agencies. The analysis provided a dynamic picture of shared influences on the interventions in different communities and in doing so offered insight into intervention effectiveness. It is argued in this article that, for examining intervention effectiveness, it is essential to have a theoretical understanding of the behaviour of the complex system in which they are implemented. This theoretical understanding has implications for the appropriate design of interventions to reduce health inequalities, and in turn should lead to more meaningful ways to evaluate them.