Randomized controlled trials (RCTs) are considered the gold standard in estimating treatment effects. When an RCT is infeasible, regression modeling or statistical matching are often used instead. Nonexperimental methods such as these could produce unbiased estimates if the underlying...

This paper draws on data and experiences observing and analyzing school lotteries from the National Evaluation of Charter School Impacts (Gleason et al., 2010) to describe the challenges associated with lottery-based research. In that study, covering 36 charter middle schools in 15 states, we...