Lessons from San Francisco: health impact assessments have advanced political conditions for improving population health.

Health impact assessment is a structured decision support tool used to systematically characterize the anticipated health effects, both adverse and beneficial, of societal decisions. In San Francisco, the use of health impact assessments has not only produced evidence to inform health policy decision making but has also contributed to the political conditions needed to achieve optimal population health. Health impact assessments have helped increase public awareness of the determinants of health, routine monitoring of these determinants, cooperation among institutions, health-protective laws and regulations, and organizational networks for health advocacy and accountability. Drawing on more than a decade of local experience, we identify the direct and indirect effects of the assessments on the politics of governance as well as on health. We demonstrate that health impact assessment is both an analytic tool and a process that helps build the social institutions that can improve health.