Epidemiology & Biostatistics Theses and Dissertations

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Identification of Factors That Relate to Gestational Age in Term and Preterm Babies Using 2002 National Birth Data
(2009) Hammad, Hoda Tarek; Zhang, Guangyu; Public and Community Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Infant mortality and other subsequent handicaps have been found to be correlated with preterm births. The purpose of this study is to investigate which factors relate to gestational age in term and preterm babies using the 2002 Public-Use Natality data file. Using this data, an exploratory data analysis of both the important discrete and continuous variables will be conducted to obtain a general idea of the data set. This will be followed by the use of regression models to determine which explanatory variables best relate to gestational age. The results can be used to establish guidelines for monitoring and treatment plans for expectant mothers who are most susceptible to preterm labor.
Effects of birthplace, language and length of time in the U.S. on receipt of asthma management plans among U.S. adults with current asthma
(2009) Williams, Sonja; Carter-Pokras, Olivia; Public and Community Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Approximately 7% of the adult population in the United States suffers from asthma and only 32% of those adults have an asthma management plan, which is an important component in asthma management. Racial/ethnic minorities have higher rates of asthma and lower rates of good asthma management. There is a lack of research in examining how foreign birth and other proxy measures of acculturation may affect long term management of asthma. Using data from both the 2002 and 2003 National Health Interview Survey, this secondary data analysis examined the relationship between the receipt of asthma management plans among 18-64 year old adult asthmatics by birthplace, length of time in the U.S., and language of interview. Hispanic/Latino participants who spoke English during the interview had a 3.43 times greater odds of having an asthma management plan when compared to those who spoke Spanish (95% CI: 1.97-5.98).
Missing Data Analysis: A Case Study of a Randomized Controlled Trial
(2009) Patzer, Shaleah Mary Murphy; Zhang, Guangyu; Public and Community Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Missing data is a pervasive problem in the analysis of many clinical trials. In order for the analysis of a study to produce unbiased estimators, the missing data problem must be addressed. First, the missing data pattern must be established; second, the missingness mechanism must be determined; and third, the most appropriate imputation method for imputing the missing values must be found. The purpose of this paper is to explore the imputation methods best suited for the missing data from the Diet and Exercise for Elevated Risk Trial (DEER) in a secondary analysis of the data. The missingness pattern in the data set is arbitrary and the missingness mechanism is MAR. A simulation study suggests that the two best methods for imputation are subject-specific mean imputation and multiple imputation. I conclude that mean imputation is the best method for handling missing data in the DEER data set.
Survey on Horse-Related Injuries and Safety Practices in Maryland and Virginia
(2010) Bethune, Lisa Anne; Carter-Pokras, Olivia; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Horseback riding is a leading cause of sports injury. This thesis identifies socio-demographic characteristics of adults sustaining horse-related injuries, and factors associated with receipt of medical treatment and improvement of safety behaviors among those injured. A web-based, cross-sectional survey was conducted in Maryland and Virginia during July 1st - September 1st 2010 (n=908). Ninety-four percent (93.7%) of respondents had ever sustained a horse-related injury. Women and adults with ≥15 years of experience with horses had higher odds of injury than men and adults with <15 years of experience. Roughly half of the injured (48.2%) had received emergency treatment. The odds of receiving medical treatment for injuries occurring at a competition/show were 2.42 (1.08-5.44) times the odds of receiving medical treatment for injuries occurring at home. Provision of informational and emotional support from friends/family, healthcare professionals, or equine industry professionals was significantly associated with improving safety practices among the injured.
Association between Allostatic Load and Arthritis in NHANES Adults
(2010) Scully, Lynn; Lee, Sunmin; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Objective: To examine the cross-sectional association between allostatic load and arthritis using data from the National Health and Nutrition Examination Survey (NHANES). Methods: Complete data on 7,714 adults were included in the analysis. An allostatic load (AL) index, comprising of multiple regulatory systems, was calculated from 11 biomarkers. Multivariate logistic regression was used to estimate the odds ratio (OR) for the association between allostatic load and arthritis, while accounting for confounders. Results: Significant positive associations were found between both continuous allostatic load (OR=1.12, 95% CI= 1.08-1.17) and the two highest quartile categories of AL and arthritis compared to the lowest quartile (quartile 3: OR=1.73, 95% CI=1.38-2.17, quartile 4: OR=1.79, 95% CI=1.41-2.26), after adjusting for confounders. The subscales of the inflammatory (OR=1.27, 95% CI=1.15-1.40) and metabolic system (OR=1.20, 95% CI=1.13-1.28) were also significant predictors. Conclusions: Cumulative biological risk is a plausible mechanism that is associated with arthritis.
Investigating Neighborhood Walkability and its Association with Physical Activity Levels and Body Composition of a Sample of Maryland Adolescent Girls
(2010) Jones, Lindsey Irene; Young, Deborah R; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Recent ecologic studies have begun to focus on characteristics of the built environment that influence physical activity (PA). Specifically, neighborhood walkability is emerging as an important determinant of PA in adults. At this point in time, there is conflicting evidence on how neighborhood walkability influences the PA levels of adolescents. The aim of this study was to investigate the relationship between individual's neighborhood walk score and individual's body mass index, body fat percentage, weight status, PA levels and meeting PA guidelines in a sample of adolescent girls. Additional analysis investigated the correlation between two objective measures of neighborhood walkability. This analysis was unable to show an association between PA levels or body composition of adolescent girls from the TAAG Maryland field site. Neighborhood walkability as assessed by the website walkscore.com was positively correlated with a GIS derived walkability index (r=.63 p<.0001).
DIAGNOSTICS FOR MULTIPLE IMPUTATION BASED ON THE PROPENSITY SCORE
(2010) Wang, Jia; Zhang, Guangyu; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Multiple imputation (MI) is a popular approach to handling missing data, however, there has been limited work on diagnostics of imputation results. We propose two diagnostic techniques for imputations based on the propensity score (1) compare the conditional distributions of observed and imputed values given the propensity score; (2) fit regression models of the imputed data as a function of the propensity score and the missing indicator. Simulation results show these diagnostic methods can identify the problems relating to the imputations given the missing at random assumption. We use 2002 US Natality public-use data to illustrate our method, where missing values in gestational age and in covariates are imputed using Sequential Regression Multiple Imputation method.
Acculturation and BMI among Chinese, Korean and Vietnamese Adults in Maryland
(2011) Chen, Lu; Lee, Sunmin; Carter-Pokras, Olivia D; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Objective: To examine the relationship between acculturation and BMI among Asian Americans. Methods: Data of 847 Chinese, Korean and Vietnamese recruited for a health education program in Maryland were included. Acculturation was measured by the short version of Suinn-Lew Asian Self-Identity Acculturation Scale (SL-ASIA) and its individual components. Height and weight were measured by trained staff. Multiple linear regression was used to estimate the parameters of acculturation variables. Results: After adjusting for confounders, SL-ASIA (β=0.71, 95% CI: 0.15, 1.26), having education in the U.S (β=0.56, 95% CI: 0.01, 1.11), younger age of arrival (0-5 years: β=3.32, 95% CI: 1.84, 4.80, 6-10 years: β=1.55, 95% CI: 0.02, 3.07) and equal preference of Asian/American food in restaurants (β=0.92, 95% CI 0.38, 1.46) were associated with BMI. The association between acculturation and BMI was stronger among men than women, and weakest among Vietnamese. Conclusion: Acculturation is moderately associated with BMI among Asian Americans.
FACTORS ASSOCIATED WITH COMPLETION OF THE HUMAN PAPILLOMAVIRUS VACCINE SERIES AMONG HISPANIC AND NON-HISPANIC WHITE ADOLESCENT GIRLS IN THE UNITED STATES
(2011) Demarco, Maria Teresa; Carter-Pokras, Olivia; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Despite recommendations of three Human Papillomavirus (HPV) vaccine shots for all adolescent girls, only 29.1% of non-Hispanic Whites and 23.4% of Hispanics achieve completion. This study describes factors associated with completion of the HPV vaccine series among Hispanic and non-Hispanic White 13-17 year old girls who initiated the series. A secondary data analysis was performed of the cross-sectional 2009 National Immunization Survey-Teen survey. Despite similar initiation rates (one in five), Hispanic girls who had initiated the series (59.9%) were less likely to complete the series than non-Hispanic Whites (76.4%). After accounting for poverty status and home ownership, Hispanics were less likely to complete the HPV vaccine series. Factors associated with HPV vaccine series initiation were age at interview and age at HPV vaccine series initiation for Hispanics; and continuous health insurance since age of 11, mother's marital status, and number of children in the household for non-Hispanic Whites.
Subtype of depression as a moderator of response in the treatment of major depression with St John's wort
(2011) Ulbricht, Christine Marie; Lee, Sunmin; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Objective: To evaluate the effect of the melancholic and anxious subtypes of depression on treatment response in the Hypericum Depression Trial. Methods: 340 adults with depression were classified according to depression subtype at baseline. Linear and logistic regression models examined the effects of depression subtype and treatment assignment on treatment response. Results: 64.41% of participants had melancholic depression and 71.76% had anxious depression. The linear regression model demonstrated that melancholic depression status at baseline and the interaction of treatment assignment and baseline melancholic status had significant effects on depression severity. The linear regression model showed significant effects only for treatment and anxious depression status at baseline on depression severity. Conclusion: While depression subtype appears to be related to certain clinical characteristics, this study was inconclusive and did not find melancholic or anxious depression subtypes to significantly moderate response to treatment with St John's wort, placebo, or sertraline.
COUNTY AND CENSUS TRACT SOCIOECONOMIC ATTRIBUTES OF ESOPHAGEAL ADENOCARCINOMA CASES SEER 15 (2000-2007)
(2011) Ghazarian, Armen Alex; Saksvig, Brit I; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Esophageal adenocarcinoma (EAC) incidence rates have increased among U.S. men. We examined associations between area-level socioeconomic attributes and stage at diagnosis, an important prognostic predictor of survival time. Logistic regression models were developed to estimate odds ratios (OR) adjusted for age, race, gender and year of diagnosis and 95% confidence intervals (CI) for localized and regional versus distant stage by census tract and county level socioeconomic attributes. At the county level, a high percent of foreign born population was associated with distant stage EAC: >15.4%-26.6%, (OR=1.15, 95% CI: 1.04-1.28) and >26.6% (OR 1.16, 95% CI: 1.03-1.31). Median household income from $40.8-$45.6K (OR=1.14, 95% CI: 1.01-1.28) was also associated with distant stage EAC. Conversely, residence in an urban county was associated with localized or regional stage EAC (OR=0.90, 95% CI: 0.82-0.98). Findings regarding area level disparities in EAC stage may inform cancer control efforts.
Examining the role of stressful life events on cognition and determining mediating and moderating pathways among postmenopausal women
(2011) Bibeau, Wendy; Young, Deborah R; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
BACKGROUND: Major life events, largely considered to be a source of great stress, are an inevitable process of the life span. Preliminary evidence suggests that the stress arising from major life events may serve as a risk factor for cognitive function decline. Evidence also indicates external (e.g., physical activity) and internal factors (i.e., psychological variables) can attenuate the physiologic effects of stress. Thus, there may be two important pathways through which stress affects health. PURPOSE: The primary aim of this dissertation was to investigate the independent and interactive effects of stressful life events on cognitive function among a sample of postmenopausal women. In addition, the possible moderating and or mediating role of external and internal factors on the relationship between stressful life events and cognitive function were examined. METHODS: Data from the Women's Health Initiative Memory Study, a randomly selected subset of the Women's Health Initiative Hormone Trial, were analyzed. To control for any treatment effects, only data from participants randomized into the placebo groups were pooled and used for all analyses, leaving a total of 3775participants. All participants had five data collections points, including baseline through four years of follow-up. Linear mixed effects models were used to answer all prospective research questions. Moderation and mediation models were used to determine presence of effect modification or mediation of external or internal variables. RESULTS: Our results appear to indicate that there was a negative relationship between stressful life events and cognitive function scores. Reporting an ill spouse/partner was associated with lower cognition scores compared to those without reporting a spouse/partner (B = -0.68, p < 0.0001). Exposure to three or more stressful life events at every data collection period was also associated with lower cognitive function scores (B = -0.61, p = 0.021). External factors did not appear to moderate this negative relationship; however, internal factors such as optimism, hostility, and negative expressiveness did. Specifically, exposure to more stressful life events was associated with less favorable psychological states, which in turn, were associated with lower cognitive function scores. CONCLUSION: Our results appear to lend support that exposure to certain life events and repeated exposure of stressful life events is associated with lower cognitive functioning. In addition, our findings provide modest evidence that psychological mechanisms are an important pathway through which stressful life events affect cognitive functioning over time among a representative sample of post-menopausal women. While stressful life events are largely unavoidable, the associated increased risk of cognitive function decline may be in part offset by various psychological factors.
SEMIPARAMETRIC AND NONPARAMETRIC ANALYSIS FOR LONGITUDINAL DATA ON THE RELATIONSHIP BETWEEN CHILDHOOD EXTERNALIZING BEHAVIOR AND BODY MASS INDEX
(2011) Wang, Kejia; He, Xin; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This thesis is an extension of the longitudinal data analysis of the association between externalizing behavior in early childhood and body mass index (BMI) from age 2 to 12 years conducted in Anderson et al. (2010). Externalizing behaviors problems are characterized by aggressive, oppositional, disruptive, or inattentive behaviors beyond those that would be expected given a child's age and development. The aim of the thesis is to estimate the children's BMI trajectory and to evaluate to what extent the externalizing behavior is related to BMI using semiparametric and nonparametric time-varying coefficient models. Some valuable insights into how the externalizing behavior and BMI are associated will be provided.
Change in Physical Activity and Associated Factors among Adolescent Girls
(2012) Zook, Kathleen Renee; Rohm Young, Deborah; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Objective: Examine relationships between changes in physical activity (PA) and personal, psychosocial and environmental factors among adolescent girls. Methods: Longitudinal data were analyzed from two cohorts of adolescent girls. Participants were placed into four categories based on PA levels. Active Maintainer-AM, Inactive Maintainer-IM, Adopter-A, or Relapser-R. Anthropomorphic, personal, psychosocial and environmental data were collected. Multivariate logistic regression was used to estimate parameters. Results: In early adolescence, Free/reduced price lunch and PA Self-Efficacy were associated with AM; Race and Friend Support for PA with IM; and Friend Support for PA with R. In later adolescence, Distance to Nearest Park, PA Frequency with Friends, and Global Physical were associated with AM; BMI, Friend Support for PA, PA Frequency with Friends, and Age at Menses, with IM; BMI with A. Conclusion: PA predictors were different across the categories and the predictors were different for early adolescence and later adolescence.
Independent and joint effects of parental attitudes and special health care needs on physical activity and screen time among chlldren and adolescents in the United States
(2012) Gingold, Janet Ann; Carter-Pokras, Olivia; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Sedentary lifestyles pose a threat to the health of children, especially those with special health care needs (SHCN). Using data from the 2007 National Survey of Children's Health, this study examined relationships between parental attitudes and low physical activity and high screen time among 6- to 17-year-olds with and without SHCN. Perceived limitation was associated with increased likelihood of low physical activity (AOR, 1.339; 95%CI, 1.079-1.662). Parenting stress (AOR, 1.189; 95%CI, 1.052-1.344) and lack of trust (AOR, 1.243; 95%CI, 1.104-1.399) were associated with increased likelihood of high screen time. Perceived limitation modified the effect of special health care needs status on high screen time. The likelihood of combined low physical activity and high screen time was greatest among children with SHCN whose parents reported both functional limitations in the child and parenting stress (AOR, 2.659; 95%CI, 1.741-4.060). Parental attitudes and SHCN should be addressed in interventions to promote active lifestyles.
Analysis of Factors Associated With Tuberculosis Outcomes in District Kullu, India
(2012) Stone, Heather; Lee, Sunmin; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
India is the country with the largest number of tuberculosis (TB) cases, contributing 20% of the global burden of infection (1) and 2 million cases annually (2). However, few if any studies have examined the epidemiology of TB in the Northern state of Himachal Pradesh. This study is a retrospective review of medical records of all tuberculosis patients (N=1086) seen at the two hospitals in Manali, District Kullu, Himachal Pradesh, India between 2008-2011. The analysis determined that being younger, female, living in a town, and/or a patient at Mission Hospital, were factors significantly associated with having extrapulmonary versus pulmonary tuberculosis (EPTB). Being older was associated with an increased likelihood of previous/complex treatment compared to new patients. Being female, from a town, and/or older were associated with receiving a non-standard regimen. Finally, patients who were previously treated/complex were significantly more likely to receive a non-standard regimen than new patients.
DOUBLY PENALIZED LOGISTIC REGRESSION FOR GENOMEWIDE ASSOCIATION STUDIES WITH LINEARLY STRUCTURED GENETIC NETWORKS
(2012) Li, Xia; Wu, Tongtong; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This research aims to integrate linear structures of genetic networks into genomewide analysis studies (GWAS). Lasso penalized logistic regression is ideally suited for continuous model selection in case-control disease gene mapping, especially when the number of predictor variables far exceeds the number of observations. But it fails to consider the structure of genetic networks. Imposing an additional weighted fused lasso can further remove irrelevant predictors. Nesterov's method is employed to handle the high dimensionality and complexity of genetic data. It also resolves the non-differentiability problem of the lasso and fused lasso penalties. In simulation studies, this proposed method shows advantages in some cases compared with lasso and fused lasso. We apply this method to the coeliac data on chromosome 8.
Measuring Allostatic Load in a Nationally Representative Sample of Pregnant Women
(2012) Selmer, Stephanie; Shenassa, Edmond; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Allostatic load (AL) is a measure of cumulative "wear and tear" on the body resulting from exposure to chronic stress. Recently, a potential link between AL and poor birth outcomes was proposed, although it is unknown whether AL can be measured in a meaningful way during pregnancy. To determine this, an AL index was created using data from the National Health and Nutrition Examination Survey (NHANES), 1999-2006. The distribution of AL scores were significantly different in pregnant and non-pregnant women (p<0.01). AL scores were associated with race, age, income, and education level in the sample of non-pregnant women, but similar associations were not seen in pregnant women. Overall, the results of this study suggest that AL does not have the same attributes in pregnant women as it does in non-pregnant women. However, the findings suggest directions for future study of AL as a risk factor for poor birth outcomes.
Sleep Duration in Adolescent Girls: Correlates and Association with Obesity Risk
(2013) Moshkovich, Olga; Saksvig, Brit I; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The present study aimed to identify demographic, behavioral, and school-related factors associated with week night sleep duration among an ethnically diverse sample of 582 adolescent girls from the Trial of Activity for Adolescent Girls (TAAG) 2. The distribution of sleep duration categories (<7 hours, 7-9 hours, and >9 hours) differed significantly among ethnic groups in bivariate analyses, but not in the final multivariate model. Additionally, sleep duration was negatively associated with distance to school from home, typical time spent on the computer, and school start time. In contrast to previous findings, shortened sleep duration was not associated with increased body mass index (BMI), body fat percentage, or quantity of moderate-to-vigorous physical activity (MVPA). Findings show support for delayed school start times. In addition, future research should examine whether interventions to reduce screen time activities among adolescents is effective in increasing their sleep duration.
THE ASSOCIATION OF ORPHAN AND VULNERABLE CHILD (OVC) PRIMARY CAREGIVING, HOUSEHOLD WEALTH, AND FEMALE AUTONOMY ON WOMEN'S BODY MASS INDEX IN NAMIBIA, SWAZILAND AND ZAMBIA
(2013) Kanamori Nishimura, Mariano Juan; Carter-Pokras, Olivia D; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Background: This dissertation investigates factors associated with orphan and vulnerable child (OVC) caregivers' body mass index (BMI) in Namibia, Swaziland and Zambia. Methods: Secondary analyses were performed using cross-sectional data from Demographic Health Surveys conducted in 2006 and 2007. Manuscript 1 included de facto women from Namibia (n=6,638), Swaziland (n=3,285), and Zambia (n=4,497). Manuscript 2 included de jure women from Namibia (n=6,305), Swaziland (n=2,786), and Zambia (n=4,389). Manuscript 3 included married de jure women from Namibia (n=2,633), Swaziland (n=1,395), and Zambia (n=2,920). Statistical analyses using data from 20-49 year old women included weighted marginal means, logistic regression, and Sobel and Goodman tests. Results: Manuscript 1. OVC caregivers' overweight prevalence ranged from 26.98% (Namibia) to 61.3% (Swaziland). Namibian OVC caregivers were less likely to be overweight than non-OVC caregivers and non-caregivers not living with OVC. Swazi and Zambian OVC caregivers were more likely to be overweight than non-caregivers. In Namibia, women's age modified the effect of the association between OVC caregiving and overweight status. Manuscript 2. Namibian and Swazi OVC caregivers had lower Absolute Wealth Index (AWI) mean scores than non-OVC caregivers and non-caregivers. In Zambia, OVC caregivers had a lower mean AWI score than non-caregivers living with an OVC but a higher mean AWI score than non-OVC caregivers. In all countries, even small increases in household wealth (e.g., being a poorer women - 2 to 3 AWI items) were associated with higher odds for being overweight regardless of women's caregiving status. Manuscript 3. Women's educational attainment increased the odds for being overweight in Swaziland and Zambia, and decreased the odds for being underweight in Namibia. Decision-making autonomy mediated the association between AWI and OVC caregivers' BMI in Zambia (Z=2.13, p=0.03). Conclusions. As Africa is experiencing a nutritional and HIV/AIDS transition, overweight problems among OVC caregivers has emerged and should be addressed. These findings support the World Health Organization's recommendations that African countries should focus on addressing infectious diseases as well as the emergence of chronic diseases. Some African public health systems and OVC programs may face a new overweight epidemic alongside existing ones such as HIV/AIDS, tuberculosis, and malaria.