Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item THE PHYSICAL AND MENTAL HEALTH EFFECTS OF ADULT CHILDREN ON FATHERS: A LONGITUDINAL STRUCTURAL EQUATION ANALYSIS(2019) Blick, Ryan; Anderson, Elaine; Roy, Kevin; Family Studies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Men are entering the later stages of life at an unprecedented rate. As fathers and their children age, a gradual transition in the hierarchy of their relationship occurs, eventually resulting in fathers being recipients, rather than providers, of care. Unfortunately, little is known about the effect that adult children (children ages 19 years old and above) have on fathers’ physical and mental health in the middle-to-late stages of life. Using a sample of 588 fathers who were between the ages of 50- and 80-years-old and who had at least one adult child, a series of structural equation models using a cross-lagged panel design were conducted to increase our understanding of 1) the nature of the associations among fathers’ physical health, mental health, relationship quality with their spouse, and relationship quality with their adult children over time in middle-to-late adulthood, and 2) how these associations change as fathers age in middle-to-late adulthood. The findings indicate that fathers’ mental health is strongly correlated with their physical health, marital relationship quality, and relationship quality with their focal child across all age groups of fathers between 57- and 80-years-old. However, a transition seems to occur for fathers between 63- and 68-years-old that increases the within-time salience of fathers’ relationship quality with their focal child. In spite of the strong bivariate correlations, the structural equation models revealed high levels of within-trait stability and a lack of cross-trait predictive power among each of these aspects of fathers’ lives across age groups. The lone exception to this was in the emergence of a significant effect from father’s mental health between the ages of 69- and 74-years-old to their father-child relationship quality six years later, suggesting the possibility of a final transition in father-child relationship dynamics late in fathers’ lives.Item A Comparison of Methods for Testing for Interaction Effects in Structural Equation Modeling(2010) Weiss, Brandi A.; Harring, Jeffrey R.; Hancock, Gregory R.; Measurement, Statistics and Evaluation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current study aimed to determine the best method for estimating latent variable interactions as a function of the size of the interaction effect, sample size, the loadings of the indicators, the size of the relation between the first-order latent variables, and normality. Data were simulated from known population parameters, and data were analyzed using nine latent variable methods of testing for interaction effects. Evaluation criteria used for comparing the methods included proportion of relative bias, the standard deviation of parameter estimates, the mean standard error estimate, a relative ratio of the mean standard error estimate to the standard deviation of parameter estimates, the percent of converged solutions, Type I error rates, and empirical power. It was found that when data were normally distributed and the sample size was 250 or more, the constrained approach results in the least biased estimates of the interaction effect, had the most accurate standard error estimates, high convergence rates, and adequate type I error rates and power. However, when sample sizes were small and the loadings were of adequate size, the latent variable scores approach may be preferable to the constrained approach. When data were severely non-normal, all of the methods were biased, had inaccurate standard error estimates, low power, and high Type I error rates. Thus, when data were non-normal, relative comparisons were made regarding the approaches rather than absolute comparisons. In relative terms, the marginal-maximum likelihood approach performed the least poorly of the methods for estimating the interaction effect, but requires sample sizes of 500 or greater. However, when data were non-normal, the latent moderated structure analysis resulted in the least biased estimates of the first-order effects and had bias similar to that of the marginal-maximum likelihood approach. Recommendations are made for researchers who wish to test for latent variable interaction effects.Item EFFECT OF CATEGORIZATION ON TYPE I ERROR AND POWER IN ORDINAL INDICATOR LATENT MEANS MODELS FOR BETWEEN-SUBJECTS DESIGNS(2006-07-28) Choi, Jaehwa; Hancock, Gregory R; Measurement, Statistics and Evaluation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Due to the superiority of latent means models (LMM) over the modeling of means on a single measured variable (ANOVA) or on a composite (MANOVA) in terms of power and effect size estimation, LMM is starting to be recognized as a powerful modeling technique. Conducting a group difference (e.g., a treatment effect) testing at the latent level, LMM enables us to analyze the consequence of the measurement error on measured level variable(s). And, this LMM has been developed for both interval indicators (IILMM; Jöreskog & Goldberger, 1975, Muthén, 1989, Sörbom, 1974) and ordinal indicators (OILMM; Jöreskog, 2002). Recently, effect size estimates, post hoc power estimates, and a priori sample size determination for LMM have been developed for interval indicators (Hancock, 2001). Considering the frequent analysis of ordinal data in the social and behavior sciences, it seems most appropriate that these measures and methods be extended to LMM involving such data, OILMM. However, unlike IILMM, the OILMM power analysis involves various additional issues regarding the ordinal indicators. This research starts with illustrating various aspects of the OILMM: options for handling ordinal variables' metric level, options of estimating OILMM, and the nature of ordinal data (e.g., number of categories, categorization rules). Also, this research proposes a test statistic of the OILMM power analysis parallel to the IILMM results by Hancock (2001). The main purpose of this research is to examine the effect of categorization (mostly focused on the options handling ordinal indicators, and number of ordinal categories) on Type I error and power in OILMM based on the proposed measures and OILMM test statistic. A simulation study is conducted particularly for the two-populations between-subjects design case. Also, a numerical study is provided using potentially useful statistics and indices to help understanding the consequence of the categorization especially when one treats ordinal data as if they had metric properties.Item NANO ELECTRIC DISCHARGE MACHINING OF GOLD THIN FILMS WITH A MODIFIED SCANNING TUNNELING MICROSCOPE(2005-05-03) Golub, Marcia A.; Gomez, Romel D; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This Master's thesis presents the development of an instrument and a technique to locally ablate solid surfaces using a scanning tunneling microscope and an electrostatic discharge processes. The design and construction of the scanning tunneling microscope inside the scanning electron microscope along with the designs of the control electronics are reported. Several methods of surface modification are investigated, namely mechanical contact and near-surface discharge in air and vacuum. Images of gold and graphite surfaces in air and vacuum, and feature formation using electrostatic discharge in air and vacuum are discussed. Analysis of the relationship between energy of the discharge and feature's size is presented, along with a discussion of the geometrical characteristics of the features.