We look at groups rather than individuals. Why do some get certain illnesses, while others do not? How do you define and select populations to study? What can you learn by studying groups that you cannot learn by studying individuals?
Populations can be studied with methodologies that range from simple description with interviews with written, audio or video records to analyses that involve complex statistical models. The challenge is to identify questions that can be answered best through population-based studies, identify appropriate populations that are available to study, implement methodologies that will help answer the questions, and translate the answers into ways to improve the health of the public.
Population-based scholarship can be organized in many ways: categories like international health and rural health define populations by place or level of economic development. Occupational and environmental health defines populations by jobs and exposures to toxic agents. Infectious and chronic disease epidemiology defines populations by the diseases they get. We also look at the impact of public policy on population health. There are many other ways to categorize population studies: by nutrition, injuries, war and disasters, poverty, age, and insurance status for instance.