The triple difference estimator

Summary Triple difference has become a widely used estimator in empirical work. A close reading of articles top economics journals reveals that the use to large extent rests on intuition. The identifying assumptions are neither formally derived nor generally agreed on. We give complete presentation triple estimator, and show even though can be computed as between two difference-in-differences estimators, it does not require parallel trend have causal interpretation. reason is biased estimators will unbiased long bias same both estimators. This requires only one assumption hold.