abstract: Methods to test hypotheses of mediated effects in the pretest-posttest control group design are understudied in the behavioral sciences (MacKinnon, 2008). Because many studies aim to answer questions about mediating processes in the pretest-posttest control group design, there is a need to determine which model is most appropriate to test hypotheses about mediating processes and what happens to estimates of the mediated effect when model assumptions are violated in this design. The goal of this project was to outline estimator characteristics of four longitudinal mediation models and the cross-sectional mediation model. Models were compared on type 1 error rates, statistical power, accuracy of confidence interval coverage, and bias of parameter estimates. Four traditional longitudinal models and the cross-sectional model were assessed. The four longitudinal models were analysis of covariance (ANCOVA) using pretest scores as a covariate, path analysis, difference scores, and residualized change scores. A Monte Carlo simulation study was conducted to evaluate the different models across a wide range of sample sizes and effect sizes. All models performed well in terms of type 1 error rates and the ANCOVA and path analysis models performed best in terms of bias and empirical power. The difference score, residualized change score, and cross-sectional models all performed well given certain conditions held about the pretest measures. These conditions and future directions are discussed. / Dissertation/Thesis / Masters Thesis Psychology 2015

The aim of this investigation was to determine whether there is a significant difference in the academic achievement of sixth grade Science students when teaching styles are matched to their learning styles. The research problem is encompassed in the following question: "Is there a relationship between matching teaching and learning styles and the academic success in Science?" A quantitative approach was undertaken, specifically, the pretest-posttest control group experimental design. The population comprised of sixth grade students selected according to a non-probability sampling method of convenience. The sample comprised of two class units randomly selected. The dependent sample t-test inferential statistic was used to analyze the data collected. The results indicated a statistically significant difference between the pretest and posttest scores of the experimental group. The conclusion reached is that matching teaching styles to learning styles improves the academic success of sixth grade learners in Science. / Educational Studies / M.Ed. (Educational Psychology)

The aim of this investigation was to determine whether there is a significant difference in the academic achievement of sixth grade Science students when teaching styles are matched to their learning styles. The research problem is encompassed in the following question: "Is there a relationship between matching teaching and learning styles and the academic success in Science?" A quantitative approach was undertaken, specifically, the pretest-posttest control group experimental design. The population comprised of sixth grade students selected according to a non-probability sampling method of convenience. The sample comprised of two class units randomly selected. The dependent sample t-test inferential statistic was used to analyze the data collected. The results indicated a statistically significant difference between the pretest and posttest scores of the experimental group. The conclusion reached is that matching teaching styles to learning styles improves the academic success of sixth grade learners in Science. / Educational Studies / M.Ed. (Educational Psychology)