Drawing on our five years of experience developing WWC evidence standards and reviewing studies against those standards as well as current literature on the design of impact studies, we highlight in this paper some of the most critical issues and common pitfalls in designing and conducting impact studies in education, and provide practical…

Data from the Sustaining Effects Study were used to investigate the impact of attrition. Four types of analyses were conducted: estimation of attrition rate by project, estimation of bias by project, prediction of bias at the project level, and estimation of bias associated with alternative aggregation procedures. Effects of attrition varied with…