Which type of observational study follows a group of people over time to see who experiences a specific outcome?

Cohort studies are a type of observational study that track a group of individuals over a period to observe how certain exposures or characteristics affect specific outcomes. In a cohort study, researchers identify a group (the cohort) based on shared characteristics or experiences, such as age, risk factors, or demographic information, and then follow them over time to monitor who develops a particular condition or outcome.

This longitudinal approach allows for the establishment of temporal relationships between exposures and outcomes, meaning researchers can see if and when certain exposures lead to specific results. For example, in a nutritional context, a cohort study might examine groups of individuals with varying dietary patterns and follow them to see how these patterns influence health outcomes like obesity or diabetes.

The other types of studies listed do not fit this description. Case-control studies typically look back at individuals who have a specific outcome (cases) and compare them with those who do not have the outcome (controls), without following them over time. Randomized controlled trials involve assigning participants to different groups to test interventions, which is distinct from observational studies. Cross-sectional studies collect data at a single point in time rather than following a cohort over time, thus lacking the temporal aspect characteristic of cohort studies.