Evaluations of educational programs or interventions are typically conducted in nonrandomly selected samples of schools or districts. Recent research has shown that nonrandom site selection can yield biased impact estimates. To estimate the external validity bias from nonrandom site selection, we combine lists of school districts that were…

As a result of the use of random assignment to treatment, randomized experiments typically have high internal validity. However, units are very rarely randomly selected from a well-defined population of interest into an experiment; this results in low external validity. Under nonrandom sampling, this means that the estimate of the sample average…

Introduction: The results of a 2009-2010 program evaluation study that examined parents, teachers of students with visual impairments, administrators, and students regarding overall satisfaction with and effectiveness of the short-term programs at a residential school for students who are blind and visually impaired are described. The findings are…