Shared-Donor Inference for Fixed-Set Heterogeneity in Synthetic Difference-in-Differences
合成双重差分中固定目标集合异质性的共享供体推断
Empirical studies often estimate several synthetic-control or synthetic Difference-in-Differences effects from a common donor pool and then summarize their heterogeneity. Because the same donors enter several comparisons, the first-stage errors are jointly distributed and affect different targets differently. We characterize three regimes for linear fixed-set summaries: nonconcentration, root-rate donor exposure, and donornegligibility. We also show that removing…