Statistical Power for Regression Discontinuity Designs in Education: Empirical Estimates of Design Effects Relative to Randomized Controlled Trials

Using data from four previously published education studies, this working paper finds that a study using a regression discontinuity design needs between 9 and 17 times as many schools or students as a randomized controlled trial to produce an impact with the same level of statistical precision. The need for a large sample is driven primarily by bandwidth selection, not adjusting for random misspecification error.