Current challenges in population health intervention research.

Population health interventions (PHIs) are generally complex; their results depend on their interaction with the context of their implementation. Moreover, the distinction between intervention and context is arbitrary: we need rather to consider an 'interventional system', including both interventional and contextual components. Evaluation must go beyond effectiveness and must include two key research questions: a viability analysis, to verify that the intervention can be routinised in a real-life context; and a theory-based evaluation, to analyse mechanisms and to understand what produces effects among components and their interactions with each other and with the context. PHI research is a question not only of the object but also of perspectives. This means doing research differently, making use of interdisciplinarity and involving stakeholders. Such an approach may contribute to the development, transfer, implementation and scaling-up of innovative interventions. © Author(s) (or their employer(s)) 2019. No commercial re-use. See rights and permissions. Published by BMJ.