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- Genre: Masters Thesis
Description
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.
ContributorsValente, Matthew John (Author) / MacKinnon, David (Thesis advisor) / West, Stephen (Committee member) / Aiken, Leona (Committee member) / Enders, Craig (Committee member) / Arizona State University (Publisher)
Created2015
Description
Research methods based on the frequentist philosophy use prior information in a priori power calculations and when determining the necessary sample size for the detection of an effect, but not in statistical analyses. Bayesian methods incorporate prior knowledge into the statistical analysis in the form of a prior distribution. When prior information about a relationship is available, the estimates obtained could differ drastically depending on the choice of Bayesian or frequentist method. Study 1 in this project compared the performance of five methods for obtaining interval estimates of the mediated effect in terms of coverage, Type I error rate, empirical power, interval imbalance, and interval width at N = 20, 40, 60, 100 and 500. In Study 1, Bayesian methods with informative prior distributions performed almost identically to Bayesian methods with diffuse prior distributions, and had more power than normal theory confidence limits, lower Type I error rates than the percentile bootstrap, and coverage, interval width, and imbalance comparable to normal theory, percentile bootstrap, and the bias-corrected bootstrap confidence limits. Study 2 evaluated if a Bayesian method with true parameter values as prior information outperforms the other methods. The findings indicate that with true values of parameters as the prior information, Bayesian credibility intervals with informative prior distributions have more power, less imbalance, and narrower intervals than Bayesian credibility intervals with diffuse prior distributions, normal theory, percentile bootstrap, and bias-corrected bootstrap confidence limits. Study 3 examined how much power increases when increasing the precision of the prior distribution by a factor of ten for either the action or the conceptual path in mediation analysis. Power generally increases with increases in precision but there are many sample size and parameter value combinations where precision increases by a factor of 10 do not lead to substantial increases in power.
ContributorsMiocevic, Milica (Author) / Mackinnon, David P. (Thesis advisor) / Levy, Roy (Committee member) / West, Stephen G. (Committee member) / Enders, Craig (Committee member) / Arizona State University (Publisher)
Created2014
Description
Maternal intrusiveness is an important predictor of child mental health problems. Evidence links high levels of maternal intrusiveness to later infant negativity, and child internalizing problems. However, children also influence the manner in which parents interact with them. For example, infants that show more negative emotionality elicit less positive parenting in their caregivers. Infant affect is also associated with later child internalizing difficulties. Although previous research has demonstrated that maternal intrusiveness is related to infant affect and child internalizing symptomatology, and that infant affect is a predictor of internalizing problems and parenting, no studies have looked at the transactional relations between early maternal intrusiveness and infant affect, and whether these relations in infancy predict later childhood internalizing symptomatology. The present study investigates young children's risk for internalizing problems as a function of the interplay between maternal intrusiveness and infant affect during the early infancy period in a low-income, Mexican-American sample. Participants included 323 Mexican-American women and their infants. Data were collected when the infants were 12, 18, 24, and 52 weeks old. Mothers were asked to interact with their infants in semi-structured tasks, and mother and infant behaviors were coded at 12, 18, and 24 weeks. Maternal intrusiveness was globally rated, and duration of infant negative- and positive affect was recorded. Mother reports of child Internalizing symptomatology were obtained at 52 weeks. Findings suggest that there are transactional relations between early maternal intrusiveness and infant negative affect, while the relations between infant positive affect and maternal intrusiveness are unidirectional, in that infant positivity influences parenting but not vice versa. Further, findings also imply that neither maternal intrusiveness, nor infant affect, influence later toddler internalizing symptomatology. Identifying risk processes in a Mexican-American sample adds to our understanding of emerging infant difficulties in this population, and may have implications for early interventions.
ContributorsRystad, Ida A (Author) / Crnic, Keith A (Thesis advisor) / Enders, Craig (Committee member) / Bradley, Robert (Committee member) / Arizona State University (Publisher)
Created2014