What is the primary purpose of directed acyclic graphs (DAGs) in epidemiology?

• A. To visualize and reason about causal structures and identify confounding paths
• B. To measure prevalence in a population
• C. To replace all statistical analyses
• D. To establish correlation only

Answer: (A)

Directed acyclic graphs in epidemiology serve as a concise visual map of causal assumptions. By representing variables as nodes and causal influences as arrows with no cycles, they show how an exposure might affect an outcome directly or through other variables, and they reveal paths that could bias an effect estimate. Identifying backdoor paths helps determine which variables to adjust for to block those noncausal routes, guiding the selection of a proper adjustment set. DAGs also illuminate the roles of mediators and colliders, helping to avoid conditioning on variables that could introduce bias. In short, their primary purpose is to clarify causal structure and inform how to adjust analyses to obtain valid causal inferences; they do not measure prevalence, replace statistical analyses, or imply mere correlation.