14.5) Common Trend Assumption in Difference-in-Difference (DD) Estimator

14.1) First-Difference Estimator

14.2) Algebra of Difference-in-Differences (DID)

14.3) Python: Diff-in-Diff (DD)

14.4) Quasi-Experiment Diff-in-Diff (DID)

14.5) Common Trend Assumption in Difference-in-Difference (DD) Estimator