Population health is “the health outcomes of a group of individuals, including the distribution of such outcomes within the group” (Kindig and Stoddart 2003).  Population health considers questions such as what factors underlie the large disparities in morbidity and mortality among social groups in the U.S., why the U.S. population’s health lags behind the health of other high income countries, why life expectancy has been declining for less educated American women, and how social, economic, environmental or other policy interventions and investments at the community, regional, and national levels might improve population health.

“Populations” are defined by geographic and/or political boundaries, and also include subgroups that share a particular social, economic, or ethnic status. Health, too, is broadly conceptualized in the range of outcomes considered — for example, life expectancy, disability, and the array of conditions that comprise physical, mental and social well-being in the population.

The field of population health science has developed over the past several decades in response to the recognition of the critical need to understand health at the population level and the often complex interplay of biologic, behavioral and contextual factors that give rise to health problems in the population. Population health science:

• – focuses on the levels of health within populations (e.g., mortality trends in the U.S.), disparities in health within populations (e.g., ethnic differences in adult diabetes in a community), and differentials in health over time and across populations (long-run trends in U.S. states’ infant mortality rates);
• – conceptualizes health as a multifactorial product of biologic, behavioral, contextual factors and their upstream and downstream interactions from “cells to society” across time and place;
• – often requires scientists to examine common etiological factors across different diseases and conditions. This approach offers possible solutions that operate at the population level to improve health not only for a given disease but also for multiple conditions; and
• – produces knowledge about the contextual, behavioral, and biological causes of health and disease, the mechanisms through which levels of health and health disparities are produced, and the evidence base for policies and practices that improve population health and ameliorate health disparities.

Population health science is an interdisciplinary field that seeks to integrate knowledge, theory, and tools from multiple disciplines – e.g., biology, the social and behavioral sciences, epidemiology, and genetics — to develop a broad understanding of the multi-factorial pathways that produce health and health disparities so that more effective solutions can be found. The field is a scientific response to the critical need to understand and address large scale and complex population health problems such as asthma, diabetes, obesity, and ethnic and socioeconomic disparities in a range of physical and mental health outcomes. Population health science recognizes that much of what determines health outcomes originates outside the clinical setting, pointing to the need for solutions that encompass the full range of clinical and non-clinical interventions, policies, and practices.