What types of health evidence persuade policy actors in a complex system?

The aim of this article is to explore the types of health evidence that diverse actors find most persuasive in a complex policy system. The impact of evidence depends on many factors, including how it is presented and translated to audiences. If diverse actors are to address complex health challenges collectively, it helps if they can draw on evidence that is accessible and meaningful to all. We explore how this can be done through a case study of promoting healthy urban development in the United Kingdom. Based on 132 in-depth interviews with critical actors from across the urban development system, we examined the types of evidence actors find most helpful. While there was some variation by sector, actors revealed a strong preference for narratives with a strong emotional impact, supported by credible evidence. Urban development decision makers are persuaded by both qualitative and quantitative evidence, although there was a slight preference among the public sector for quantitative data. All actors valued evidence on the impact of the urban environment on population health outcomes and the associated costs of ill health. There was, however, a preference among private sector actors for evidence showing economic valuations of health that demonstrate a commercial advantage. Our findings make an important contribution to the evidence-based policy literature by identifying the types of health evidence that appeal to diverse actors in the urban development system. These insights can be used to design evidence that meets the requirements of all actors in a complex system.