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Covariate-Based Diagnostics for Randomized Experiments are Often Misleading

Over the last couple of years, I’ve seen a large number of people attempt to diagnose the quality of their randomized experiments by looking for imbalances in covariates, because they expect covariate imbalances to be ruled out by successful randomization. But imbalance is, in general, not guaranteed for any specific random assignment — and, as […]