When do we know enough to recommend action on the social determinants of health?

The Robert Wood Johnson Foundation Commission to Build a Healthier America was charged to identify strategies beyond medical care to address health disparities in the U.S. related to social and economic disadvantage. Based on insights gained while providing scientific support for the commission's efforts, this paper presents an overview of major issues that arise when assessing evidence to inform policies and programs to address the social determinants of health. While many of the insights are not new, they have not been widely assimilated within medicine and public health. They have particular relevance now, given growing awareness of the important health influences of social factors. The discussion presented here is intended to highlight key considerations for researchers who study social determinants of health and policymakers whose decisions are shaped by research findings. Policies should be based on the best available knowledge, derived from diverse sources and methods. An array of tools and guidelines is now available to guide the assessment of evidence on the social determinants of health, building on--and going beyond--principles first articulated in the "Evidence-Based Medicine" movement. The central thesis of the current paper is that the standards for evidence to guide social policies must be equally rigorous but also more comprehensive than those traditionally used to inform clinical interventions, because social policies must deal with upstream factors that affect health through complex causal pathways over potentially long time periods.