This paper investigated consequences of measurement error in the pretest on the estimate of the treatment effect in a pretest-posttest design with the analysis of covariance (ANCOVA) model, focusing on both the direction and magnitude of its bias. Some prior studies have examined the magnitude of the bias due to measurement error and suggested…

Pretest-posttest experimental designs are often used in randomized control trials (RCTs) in the education field to improve the precision of the estimated treatment effects. For logistic reasons, however, pretest data are often collected after random assignment, so that including them in the analysis could bias the posttest impact estimates. Thus,…

A computer simulation procedure was developed to reproduce the overall pattern of results obtained in the Educational Testing Service Growth Study. Then simulated data for seven sets of 10,000 to 15,000 cases were analyzed, and findings compared on the basis of correlations between estimated and true growth scores. Findings showed that growth was…