14.1) First-Difference Estimator
https://youtu.be/p9NhSrTugYM
14.2) Algebra of Difference-in-Differences (DID)
https://youtu.be/_mOJK8A6nR0
14.3) Python: Diff-in-Diff (DD)
https://youtu.be/lxgGqV5zfnw
14.4) Quasi-Experiment Diff-in-Diff (DID)
https://youtu.be/jDEe8qhpzRc
14.5) Common Trend Assumption in Difference-in-Difference (DD) Estimator
https://youtu.be/B-Y4GpPYJ4Q
14.6) Introduction to Difference-in-Differences (DiD)
https://youtu.be/qaSV2lx3K7c
