Difference-in-Differences website (with Bret Zeldow and Laura Hatfield).Difference-in-DifferencesFoundational proofs in design-based causal inference, presented with greater step-by-step detail than standard expositions for improved clarity and understanding.Unbiasedness of Difference-in-Means estimatorDerivation of Difference-in-Means estimator’s varianceConservative estimation of Difference-in-Means estimator’s variance
