Sample Size Requirements for Education Multi-Site RCTs That Select Sites Randomly
*Names in bold indicate Presenter
This paper provides plausible estimates of the sample size requirements for multi-site RCTs in education that select schools randomly. These estimates are based heavily on already published evidence from large-scale randomized trials on the variation in impacts across sites—a key statistical power parameter for this type of design. In addition, we contribute one additional piece of evidence on cross-site impact variation from a study of charter schools, which was selected because the effects of charter schools almost surely vary more than the effects of most educational interventions. This allows us to put a plausible upper bound (though clearly not a mathematical upper bound) on the cross-site impact variance and thus the sample size requirements for multi-site RCTs in education that select sites randomly.