Most randomized field experiments experience some attrition. Moreover, the extent of attrition may differ by treatment condition in systematic, non-random ways, biasing estimates of treatment effects and contributing to invalid inferences. We address concerns about non-random attrition by quantifying the conditions necessary in the attritted data…

I discuss three common practices that obfuscate or invalidate the statistical analysis of randomized controlled interventions in applied linguistics. These are (a) checking whether randomization produced groups that are balanced on a number of possibly relevant covariates, (b) using repeated measures ANOVA to analyze pretest-posttest designs, and…

Head Start is the largest publicly funded preschool program in the U.S., and one of its primary goals is to improve the school readiness of low-income children. As has been widely reported, the first randomized trial of Head Start in the program's history found some evidence that it is achieving this goal. Receiving one year of Head Start had…