A longitudinal cohort study is a type of research design that involves following a group of individuals over a period of time to observe how their characteristics or behaviors change. This type of study allows researchers to examine trends, causality, and the effects of certain factors on outcomes over time. Longitudinal cohort studies are often used in epidemiological research to track the development of diseases or health outcomes in a population. They are also used in social science research to study changes in attitudes, behaviors, or other variables over time.