Public health and transportation literature documents links between walking and overall wellbeing among people of all ages. However, quantifications of these links frequently reflect only one type of walking, such as exercise walking or walking for transportation. Often, this work concentrates on healthy, working age adults. This results in limited understanding of how total walking cumulatively relates to overall health status, especially among other populations. Demographic shifts in the United States will result in population aging, which informs a sense of urgency around understanding how older and more disability-burdened groups will engage in walking, and how socioeconomic contexts in which they reside will shape these patterns. This dissertation used data from the 2017 National Household Travel Survey, which measures travel behaviors to quantify total walking patterns among subsamples of older adults, people with disabilities, and young adults. Each of the three interrelated studies used a theoretical framework informed by the Life Course Perspective and Social Ecological Model to develop multivariable statistical models predicting walking outcomes. Findings indicate that older adult walking frequency correlates most strongly with gender, overall health status, and household vehicle access. Mobility disability status, overall health status, use of mobility devices, and educational attainment were also highly correlated with any walking among older adults. Among disabled and non-disabled working-age adults, number of household vehicles and population density of residential area correlated with total weekly walk count; health and disability statuses did not. Mobility disability and health statuses did, however, predict odds of participation in any total walking in the past week among this group. Among young adults (18-25,) patterns in total walking vary according to immigrant status. Each study contextualizes these results and potential applications to public health research and practice. For example, findings could help guide community-based organizations’ interventions to promote walking, highlighting specific subpopulations amenable to such efforts. Taken together, results of this dissertation highlight the need for more nuanced analyses of walking as it relates to physical activity and transportation mobility, both of which relate to overall wellbeing across the life course.

Bullying during childhood and adolescence can negatively influence various aspects of youth development and long-term well-being. Adults who were bullied as children or adolescents are more likely to struggle with mental health problems such as panic disorders and anxiety, while adolescent bullies are more likely to engage in violent behaviors later in life. Yet, bullying is a common experience for many youths around the world and global surveys estimate that approximately one in three adolescent males and one in four females have been the target of bullying at school.

This dissertation focuses on adolescent bullying in Latin America and the Caribbean, a region of the world affected by high levels of intentional violence among youth, but that so far has been relatively under-researched. Together, these three papers explore the role of socioeconomic factors at the individual and school levels and assess the national policy landscape in the region. The first paper focuses on the relationship between student socioeconomic status and different dimensions of bullying victimization (e.g. physical and verbal). The second paper investigates how the school’s socioeconomic context relates to student bullying victimization. These two papers use data from the 2015 Program for International Student Assessment (PISA). The third paper provides an overview of the antibullying legislative context in Latin America and the Caribbean. This paper includes a descriptive analysis of existing school-based antibullying laws and uses both empirical and iterative methods to create a quantitative legal dataset, which is subsequently used to assess the scope of existing laws, bullying definitions, and preventive measures.

Analyses of the PISA data reveal a sizeable number of missing data, especially among more vulnerable students. Data completeness also varies across participating countries. These findings highlight the difficulties of conducting large international assessments and should support future studies on the topic by underscoring measurement challenges and existing data gaps. Results from the last paper indicate most countries in the region have yet to adopt national antibullying laws. Nevertheless, encouraging signs included the fact that the most populous countries in the region have laws in place and that new laws have steadily emerged over the past ten years.

Progression to end stage kidney disease (ESKD) is often sudden due to few symptoms during earlier stages of chronic kidney disease (CKD), and health care access barriers preventing recommended CKD screening. Due to nonrandom processes dictating selection into pre-ESKD nephrology care, permanent access versus catheter, and arteriovenous graft (AVG) versus arteriovenous fistula (AVF), measurement of outcomes subsequent to these processes must consider remedies to potential selection bias. In paper one, a recursive bivariate probit estimated factors associated with permanent access creation prior to hemodialysis after accounting for selection into pre-ESKD nephrology care. Nearly all patient factors had small effects, whereas pre-ESKD nephrology care increased the likelihood of improved care (permanent access) more than fourfold. Polices related to health insurance access and pre-ESKD nephrology care are therefore essential for improving rates of early permanent access creation. Paper two examines determinates of vascular access type and infection, with some factors (e.g., pre-ESKD nephrology care) relating to infection risk indirectly, through selection into an access type. An endogenous Poisson was used to model variability in hospitalization for vascular access infection after adjusting for selection into permanent access. The results suggest ESKD patients under 30, patients with a history of intravenous drug use, and residents of nursing homes should be a focus of interventions to reduce vascular access infection among ESKD patients, as adjustment for selection into an access type substantially increased estimates of these groups’ infection risks, relative to estimates from a Cox proportional hazards model that does not correct for selection bias. In paper three, rates of filled opioid prescription did not differ by access type, and a modeling approach accounting for selection into AVF versus AVG was found to be inappropriate. However, among patients filling an opioid prescription, AVG recipients had, on average, 2 additional 5 milligram hydrocodone equivalents prescribed to them relative to AVF recipients. Federal, state, and health system policymakers, as well as members of surgical societies and research scientists, may wish to use these findings to inform methodological approaches and decisions related to the identification and care of late-stage CKD and early-stage ESKD patients.

Persons infected with SARS-CoV-2 during pregnancy are at increased risk of severe COVID-19, including hospitalization, mechanical ventilation, and death. The effects of the pandemic on maternal mortality and morbidity in Brazil, a country disproportionately impacted by COVID-19, have not been well-characterized. We set out to quantify the effect of the COVID-19 pandemic on maternal mortality in Brazil, as well as identify individual, municipal, and state factors that impacted COVID-19-related maternal mortality and morbidity during the pandemic. Using publicly-available databases through the Brazilian Ministry of Health, we estimated 4,995 maternal deaths from January 1, 2020 to December 31, 2021. Using two complementary forecast models, we demonstrated that the observed maternal mortality ratio (MMR) in 2021 was more than double the predicted MMR based on historical maternal mortality data. From January 1, 2021 to December 31, 2021, there were 10,435 pregnant or postpartum persons hospitalized with COVID-19 in Brazil, of which 1,059 (10.1%) resulted in death. Using a random effects model, a single dose of an approved COVID-19 vaccine prior to hospitalization reduced the odds of maternal death by 66%, and estimated state vaccine coverage >90% reduced the odds of maternal death by 89%. Among this hospitalized population, 3,055 individuals required an intensive care unit (ICU) admission. Using nested logistic regression models (LRMs) and multilevel models (MLMs) to incorporate both individual-level and municipal-level factors, we found that COVID-19 vaccination reduced the odds of maternal ICU admission by 38%. Municipal-level health factors, including high family health strategy coverage and ICU bed rates, were not significantly associated with protection against ICU admission when controlling for clustering in the LRM, or in the MLM with inclusion of municipal-level factors. The national COVID-19 vaccination campaign, including targeting pregnant and postpartum individuals, should remain a cornerstone of the Brazilian public health armamentarium in efforts to reduce the national MMR, and protect against maternal death and ICU admissions due to COVID-19.

A growing literature has explored the relationship between life course factors and health in later life. In particular, childhood circumstances have been shown to be associated with several health outcomes many decades later. Most of this literature has focused on high-income countries and on associations between single events or exposure variables in childhood and individual health outcomes among older adults. Less is known about the combined effect of harmful exposure in childhood on later-life health outcomes and, especially, in lower- and middle-income countries. Also, imperfect strategy identifications in observational studies make difficult to assess the robustness of these associations.

This dissertation aims to address this gap in the literature with three separate studies on the relationship between childhood disadvantage and several later-life health outcomes among Brazilians aged 50 and over using data from the baseline assessment of the Brazilian Longitudinal Study of Aging. The first study sheds light on the associations between several potentially harmful exposures in childhood (separately and combined) and the occurrence of chronic conditions, separately and together (multimorbidity). The second study focuses on the impact on distinct theoretically appropriate domains of childhood disadvantage on three measures of cognitive performance. These first two studies also investigate the potential mediation effect of adulthood socioeconomic status (SES) on these relationships. And the last study discusses the appropriateness of a novel sensitivity framework (SenseMakr) to analyze observational studies by analyzing the robustness of 65 hypothesized associations between individual exposure and outcome variables.

Results from the first study shows that a childhood disadvantage scale was associated with 8 different chronic conditions as well as the total count of chronic conditions. Mediation analyses suggest that part of the effect of childhood disadvantage (10%) on multimorbidity is mediated by higher SES in adulthood, while extensive sensitivity analyses suggest that omitted confounding is very unlikely. In the second study, we found that childhood disadvantage is associated with low performance in memory tests and semantic verbal fluency tests among older Brazilians. Adulthood SES fully mediated the association between all domains of childhood disadvantage and memory performance and only partially mediated its association with verbal fluency. The last study found that out of the 65 possible associations between single exposure and outcome variables, 24 were found to be statistically significant. Although the SenseMakr framework does not provide thresholds to support any mechanistic conclusion as it is not possible to establish universal cutoff values for its robustness measures, this approach can be highly useful in other observational studies of aging and the life course.

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