Test undergraduate students' understanding of confounding and causal identification in observational studies, including how to construct and interpret directed acyclic graphs (DAGs) to identify confounders, colliders, and mediators; choose and justify common adjustment methods (regression, stratification, matching, propensity scores, IPTW); and recognize assumptions and limitations (exchangeability, positivity, unmeasured confounding, overadjustment) when estimating causal effects.