Study Designs
Environmental epidemiology uses several study designs to establish links between exposures and health outcomes. Cross-sectional studies measure exposure and disease at one point in time—useful for generating hypotheses but unable to establish causation. Cohort studies follow exposed and unexposed groups over time to compare disease incidence—the Framingham Heart Study and the Nurses' Health Study are landmark examples. Case-control studies compare past exposures between people with disease (cases) and without (controls)—efficient for rare diseases. Ecological studies compare populations (e.g., cancer rates in counties with vs. without a chemical plant). Each design has strengths and limitations in establishing causation, and the strongest evidence comes from consistent findings across multiple study types.