Type of Document	Dissertation
Author	Petscher, Yaacov M.
Author's Email Address	ypetscher@fcrr.org
URN	etd-06042009-150245
Title	A Simulation Study On The Performance Of The Simple Difference And Covariance Adjusted Scores In Randomized Experimental Designs
Degree	Doctor of Philosophy
Department	Psychology, Department of
Advisory Committee	Advisor Name Title Christopher Schatschneider Committee Chair Jon Maner Committee Member Richard Wagner Committee Member Young-Suk Kim Committee Member Akihito Kamata Outside Committee Member
Keywords	Monte Carlo Randomized Experiment Gain Score
Date of Defense	2008-11-14
Availability	unrestricted
Abstract A Monte Carlo simulation was conducted to examine the conditions under which the simple difference and residualized change scores were more or less powerful than each other, and if the two estimators produced a biased estimate of the average treatment effect. Five factors were manipulated in the design including: sample size, normality of the pretest and posttest distributions, average treatment effect, the correlation between pretest and posttest, and posttest variance. A 5 x 5 x 3 x 4 x 4 mostly-crossed design was run with 1,000 replications per condition, resulting in 905,000 conditions. Results suggested that the covariance adjusted score in an ANCOVA designed should be used in pretest-posttest randomized experiments when power is of interest. Additionally, neither estimator produced a biased estimate of the average treatment.
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