Test students' ability to apply difference-in-differences to assess a regulatory policy's effect on firm performance, including defining treatment and control groups, verifying identification (parallel trends), selecting appropriate specifications (two-way fixed effects, event-study, handling staggered adoption), choosing estimation practices (clustering, standard errors), diagnosing threats (anticipation, spillovers, sorting), conducting robustness checks (placebo tests, pre-trend tests, heterogeneous effects), proposing corrective estimators or reweighting, and interpreting coefficient magnitudes and policy implications using firm-level panel data.