Anna Matheson, Mat Walton, Rebecca Gray, Kirstin Lindberg, Mathu Shanthakumar, Caroline Fyfe, Nan Wehipeihana, Barry Borman

This article outlines the methods being used to evaluate a community-based public health intervention. This evaluation approach recognizes that not only is the intervention, Healthy Families NZ, complex, but the social systems within which it is being implemented are complex. To address challenges related to complexity, we discuss three developing areas within evaluation theory and apply them to an evaluation case example. The example, Healthy Families NZ, aims to strengthen the prevention system in Aotearoa/New Zealand to prevent chronic disease in 10 different geographic areas. Central to the evaluation design is the comparative case method which recognizes that emergent outcomes are the result of 'configurations of causes'. 'Thick', mixed-data, case studies are developed, with each case considered a view of a complex system. Qualitative Comparative Analysis is the analytical approach used to systematically compare the cases over time. This article describes an approach to evaluating a community-based public health intervention that considers the social systems in which the initiative is being implemented to be complex. The evaluation case example provides a unique opportunity to operationalize and test these methods, while extending their more frequent use within other fields to the field of public health.