[Evaluating population health interventions: The contributions of theory-driven evaluations]

Population health intervention research has been characterized by the deployment of scientific methods designed to produce knowledge on policy and program interventions directly or indirectly involving the health sector, and potentially affecting population health. The proposed solutions encompass a multitude of interventions of variable types, scale, focus and implementation, rendering them particularly complex and difficult to understand. This complexity raises major conceptual and methodological issues because in reality, we assess not an intervention, but rather a set of interventional elements interacting with those specific to the context in which they appear. It is the interactions that produce effects, to the extent that it makes little sense to speak of an intervention, and more sense to consider an interventional system defined by the interactions. To grasp the numerous elements brought into play, it behooves us to amalgamate evaluation paradigms and approaches. In a precise context, theory-driven evaluations are of pronounced interest. This article presents the main principles of this type of evaluation by focusing on its capacity to shed light on the stakes involved in intervention/context interplay, and by putting forward conclusions transferable to population health research.