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Contributions To Multivariate Matching In Observational Studies
Get PDFMatching is a common approach to reduce bias in observed covariates to draw reliable causal inferences in observational studies. This thesis consists of three papers discussing new methods for conducting, evaluating, and improving matching designs in observational studies. The first paper presents new optimal matching techniques for large-scale observational data. This new method reduces the computational complexity and preserves appealing properties in terms of balancing covariates. After constructing a matched sample, it is essential to assess the covariate balance of the matched data since lack of balance in covariates can induce a bias of the estimated treatment effect. The second paper discusses a formal evaluation of covariate balance. This new assessment evaluates whether the match is adequate compared to randomized experiments and identifies the major problems, guiding how to improve the covariate balance. If diagnostics suggest that the current match is not satisfactory, how can we improve the quality of matched samples? The final paper utilizes the idea of directional penalties, which can improve covariate balance in a matched sample effectively, even for a large observational study
Limit Theorems For Dependent Combinatorial Data, With Applications In Statistical Inference
Get PDFThe Ising model is a celebrated example of a Markov random field, which was introduced in statistical physics to model ferromagnetism. More recently, it has emerged as a useful model for understanding dependent binary data with an underlying network structure. This is a discrete exponential family with binary outcomes, where the sufficient statistic involves a quadratic term designed to capture correlations arising from pairwise interactions. However, in many situations the dependencies in a network arise not just from pairs, but from peer-group effects. A convenient mathematical framework for capturing higher-order dependencies, is the p-tensor Ising model, which is a discrete exponential family where the sufficient statistic consists of a multilinear polynomial of degree p. This thesis develops a framework for statistical inference of the natural parameters in p-tensor Ising models. We begin with the Curie-Weiss Ising model, where every p-tuple of nodes interact with equal strengths, where we unearth various non-standard phenomena in the asymptotics of the maximum-likelihood (ML) estimates of the parameters, such as the presence of a critical curve in the interior of the parameter space on which these estimates have a limiting mixture distribution, and a surprising superefficiency phenomenon at the boundary point(s) of this curve. However, ML estimation fails in more general p-tensor Ising models due to the presence of a computationally intractable normalizing constant. To overcome this issue, we use the popular maximum pseudo-likelihood (MPL) method, which avoids computing the inexplicit normalizing constant based on conditional distributions. We derive general conditions under which the MPL estimate is root N-consistent, where N is the size of the underlying network. Our conditions are robust enough to handle a variety of commonly used tensor Ising models, including spin glass models with random interactions and the hypergraph stochastic block model. Finally, we consider a more general Ising model, which incorporates high-dimensional covariates at the nodes of the network, that can also be viewed as a logistic regression model with dependent observations. In this model, we show that the parameters can be estimated consistently under sparsity assumptions on the true covariate vector
Parents’ Perceptions Of Safety In Public Space And Adolescent Well-Being In Ethiopia, Peru, And Vietnam
Get PDFSafety in public space is a critical concern, particularly for women and girls, and these concerns may have consequences for well-being. Most scholarship to date, however, is cross-sectional; little is known about the longer-term impact of perceiving public space as unsafe. Among adolescents, the relationship between safety and well-being is likely influenced by parents. This study used longitudinal analysis to examine the factors that contribute to parents’ perceptions of adolescent safety at age 15, the relationship between these perceptions and adolescent well-being at age 19, and the differences for boys and girls. Data were drawn from Young Lives, a multi-country panel study. The sample included 820 parent/adolescent dyads in Ethiopia, 620 in Peru, and 941 in Vietnam. Descriptive statistics and multivariate regressions were conducted. Perceiving one’s child unsafe in public space was highest in Peru (two in three parents), followed Vietnam (one in three parents), and Ethiopia (one in five parents). In the adjusted analyses, there were two significant findings. In Ethiopia and Peru, girls were more likely than boys to be perceived as unsafe. Adolescents in certain regions of Ethiopia and Vietnam also were more likely to be perceived as unsafe. No associations were detected between parents’ perceptions of adolescent safety at age 15 and adolescent well-being at age 19. Parents’ concerns for adolescent safety are substantial, especially in Peru. Girls’ safety is of particular concern and deserves more public health attention. The regional variation in parents’ perceptions suggests that it is a local phenomenon and requires locally-driven intervention. Although no association between parents’ perceptions of safety and adolescent well-being was found, prior research supports this link. Young Lives provided one of the few data sets equipped to examine this relationship longitudinally, however, it had limitations – offering just a single item measure for safety concerns. Better data is needed. This investigation lays the groundwork for subsequent research, which is needed, and should: utilize a robust measure of perceptions of safety; consider the importance of other community factors (e.g., rates of violence); and test additional measures of well-being; physical and mental health would offer important contributions to the field
Geometric Approaches To Quantum Fields And Strings At Strong Couplings
Get PDFGeometric structures and dualities arise naturally in quantum field theories and string theory. In fact, these tools become very useful when studying strong coupling effects, where standard perturbative techniques can no longer be used. In this thesis we look at several conformal field theories in various dimensions. We first discuss the structure of the nilpotent networks stemming from T-brane deformations in 4D N=1 theories and then go to the stringy origins of 6D superconformal field theories to realize deformations associated with T-branes in terms of simple combinatorial data. We then analyze non-perturbative generalizations of orientifold 3-planes (i.e. S-folds) in order to produce different 4D N=2 theories. Afterwards, we turn our attention towards a few dualities found at strong coupling. For instance, abelian T-duality is known to be a full duality in string theory between type IIA and type IIB. Its nonabelian generalization, Poisson-Lie T-duality, has only been conjectured to be so. We show that Poisson-Lie symmetric sigma-models are at least two-loop renormalizable and their beta-functions are invariant under Poisson-Lie T-duality. Finally, we review recent progress leading to phenomenologically relevant dualities between M-theory on local G_2 spaces and F-theory on locally elliptically fibered Calabi-Yau fourfolds. In particular, we find that the 3D N=1 effective field theory defined by M-theory on a local Spin(7) space unifies the Higgs bundle data associated with 4D N=1 M-theory and F-theory vacua. We finish with some comments on 3D interfaces at strong coupling
Cellular Plasticity And Heterogeneity: Implications In Tumor Cell Invasion And Metastasis
Get PDFThe existence of heterogenous subpopulations of cells in cancer has been shown to arise via natural evolution or through movement between cellular states collectively known as “cellular plasticity.” This heterogeneity and plasticity are critical drivers of phenotypic diversity culminating in many facets of disease progression, such as metastasis. While the existence of heterogeneity and cellular plasticity are well accepted, the molecular underpinnings and functional outcomes, such as metastasis, of these populations remains limited. Here, we first investigated a form of cellular plasticity known as epithelial-to-mesenchymal transition (EMT) and dissect the molecular mechanisms of a recently described partial EMT (P-EMT) state operating in vivo in a mouse model of pancreatic ductal adenocarcinoma (PDAC), whereby tumor cells lose their epithelial state through a post-translational mechanism. This is distinct from complete EMT (C-EMT), which achieves the transition transcriptionally, through regulation of a complex hierarchy of EMT transcription factors (EMT-TFs). We report that prolonged calcium signaling in carcinoma cells induces a P-EMT phenotype characterized by the internalization of membranous E-cadherin (ECAD) and an increase in cellular migration and invasion. These effects can be recapitulated by signaling through Gaq-associated G-protein coupled receptors (GPCRs) and are mediated through the downstream activation of calmodulin. These results implicate calcium signaling as a potent driver of epithelial-mesenchymal plasticity in cancer cells that may be important for the metastatic cascade. We subsequently investigated other potential mechanisms of metastasis that may occur as tumors evolve de novo. Specifically, we analyzed paired primary tumors and metastases using a multi-fluorescent lineage-labeled mouse model of PDAC. Genomic and transcriptomic analysis revealed, for the first time, an association between metastatic burden and amplification of MYC. Mechanistically, we found that MYC promotes metastasis by recruiting tumor associated macrophages (TAMs), leading to greater bloodstream intravasation. Consistent with these findings, metastatic progression in human PDAC was associated with activation of MYC signaling pathways and enrichment for MYC amplifications specifically in metastatic patients. These results implicate MYC activity as a major determinant of metastatic burden in advanced PDAC. Thus, using novel mouse models of PDAC, we identified key pathways, genetic and non-genetic, that regulate cellular plasticity and lead to increased invasion and metastatic spread. The identification of these pathways and regulators represent an avenue for combating the most lethal aspects of tumor progression, metastasis and therapy resistance
Consumer Behavior And Firm Marketing Strategy Under Assortment Expansion
Get PDFThis dissertation studies two types of assortment expansion strategies: category expansion and the launch of a new service. We first explore the impact of category expansion on customer demand and firm pricing strategy. We theoretically and empirically demonstrate the dark side\u27\u27 of category expansion: the price sensitivity of existing categories may increase. We develop a model of multi-category purchase with travel costs to capture customers\u27 preference for one-stop shopping—the primary motivation for category expansion. We then apply the model to study the price sensitivity of grocery categories after liquor was introduced to private stores in the state of Washington due to a deregulation policy. Contrary to conventional wisdom, we find price sensitivity increases in categories low in demand and complementary to liquor. These changes, if ignored, would lead to a significant profit loss. Next, we study the pricing strategy of the newly introduced category post assortment expansion. Specifically, we examine how and why liquor prices change after privatization in the state of Washington. We propose five mechanisms and develop a framework to analyze their price effect using counterfactual simulations. Our results suggest that, contrary to the policymaker\u27s expectation, competition does not lower liquor prices. Rather, liquor prices surge because of the high license fees. Finally, we examine the impact of a subscription program on customer purchases. We adopt a quasi-experimental method to identify individual-level treatment effects. We find the subscription program leads to a large increase in customer purchases. The effect of the subscription program is economically significant, persistent over time and heterogeneous across customers. Interestingly, the program’s economic benefits only explain a third of the effect size. Evidence suggests that customers commit a sunk cost fallacy in that they increase purchases to justify their subscription decisions
Politics And Prosthetics: 150 Years Of Disability In Japan
Get PDFIn this dissertation, I argue that attempts by activists and policy makers to improve access to Japan’s built environment, education, employment, entertainment, and welfare systems for disabled populations over the last one hundred and fifty years have not always helped impaired individuals and frequently excluded as many demographics as they empowered. To identify which groups of people have been privileged with access and why, I analyze government records, news reports, and documents from advocacy organizations using approaches from history, anthropology, sociology, political science, and media studies. My evidence suggests that economic pressures tied to processes such as industrialization, democratization, and ageing have played a key role in shaping the politics of accessibility in modern Japan, as they have led architects, engineers, educators, and other stakeholders to focus on the needs of individuals with diverse impairments at different points in time. Equally influential have been international flows of information, materials, and people in the disability welfare sphere, which have pushed politicians to pursue domestic reforms. My project demonstrates why scholars of Japan must explore technologies created by and for disabled people to fully appreciate numerous aspects of the country’s culture, ranging from military actions and modes of governance to marketplace and material innovations. It also explains why academics interested in social justice issues in places like the United States and Europe must strive to investigate the history and politics of disability in Japan. Why does Japan matter? Because Japan has the third largest economy and fastest ageing population in the world. Interested parties often export its assistive technologies overseas, and the nation’s access-making activities have served, and likely will continue to serve, as successful models to emulate and cautionary tales of what to avoid for other countries. A descriptive project with prescriptive implications, this dissertation uses history to shape policy by asking policy makers to consider who has a seat at the table, how they come to be there, and what they fail to imagine when making access measures. By unpacking the politics of access in Japan’s past and present, this project helps create an inclusive future
The Online Adjustment Of Speaker-Specific Phonetic Beliefs In Multi-Speaker Speech Perception
Get PDFThis dissertation examines how listeners\u27 knowledge of interspeaker variability guides their generalization of perceptual learning in multi-talker listening. A series of perceptual learning experiments are conducted to evaluate whether listeners generalize what they have learned about a previous talker\u27s production of sibilants and stop VOT to another speaker either of the same gender or a different gender. Experiment 1 and 2 finds that the perceptual learning of sibilants constantly generalizes across speakers of different genders under an acoustics-phonology mismatch constraint. The constraint states that perceptual learning fails to generalize if there is a mismatch between the directions of perceptual shifts intended by the raw acoustic distributions of stimuli and by their phonological distribution in the perceptual space. Experiment 3 reports evidence for the perceptual generalization of stop VOT across speakers of different genders. These results lend support to a cumulative update account, which suggests that perceptual learning updates across speakers in such a way where previous and current perceptual learning experiences are re-integrated to form a cumulative perceptual expectation that listeners use for upcoming perception events. Building on the above findings, Experiment 4 investigates the constraints of speaker identity and gender on the perceptual generalization of sibilants and stops by introducing and manipulating visual identity and voice gender cues. The results show reduced magnitude for perceptual generalization across genders than within gender, and, in the latter case, for perceptual generalization across speakers than within speaker. These results raise the possibility that socioindexical specificity imposes a constraint on perceptual learning by modulating the magnitude of perceptual generalization across social groups, instead of blocking its occurrence. They also suggest that listeners\u27 knowledge of structure in talker variability may be more fine-grained than hard-and-fast bindings of social-demographic groups and lend support to the sophisticated interweaving of social information in the architecture of the phonetics-phonological mapping system
The Stigmatized Consumer: Role Of Language And Diversity On Consumer Behavior
No full textWhile millions of consumers deal with various stigmatized identities such as obesity, homelessness, and substance use disorders, little is known about how identity cues within the marketplace may influence how they are perceived and supported by others as well as when these cues are most effective in attracting stigmatized consumers. This dissertation investigates how language (e.g., homeless person versus person experiencing homelessness) and cultural diversity influences various consumption behaviors for both stigmatized and non-stigmatized consumers. Essay 1 deals with how language choices used for stigmatized groups may be driven by lay beliefs surrounding the stigmatized identity. Using lab experiments and archival data, my work suggests that when people condition as more changeable, they are more likely to identity-first (vs. person-first) language. Essay 2 addresses how language choices, specifically person-first language, may lead to increased motivation to engage with brands and feelings of inclusivity for stigmatized consumers. Essay 3 explores the use of cultural diversity within marketing schemes and its impact on market reaction for Black and White consumers. Through lab studies, my work suggests that using multicultural diversity by brands focused on marginalized consumers may lead to less positive market reaction. These essays provide a straightforward yet nuanced approach for organizations to improve experiences for all stigmatized consumers in both society and the marketplace
Material Point Methods For Simulating Material Fracture
No full textMaterial fracture surrounds us every day from tearing off a piece of fresh bread to dropping a glass on the floor. Modeling this complex physical process has a near limitless breadth of applications in everything from computer graphics and VFX to virtual surgery and geomechanical modeling. Despite the ubiquity of material failure, it stands as a notoriously difficult phenomenon to simulate and has inspired numerous efforts from computer graphics researchers and mechanical engineers alike, resulting in a diverse set of approaches to modeling the underlying physics as well as discretizing the branching crack topology. However, most existing approaches focus on meshed methods such as FEM or BEM that require computationally intensive crack tracking and re-meshing procedures. Conversely, the Material Point Method (MPM) is a hybrid meshless approach that is ideal for modeling fracture due to its automatic support for arbitrarily large topological deformations, natural collision handling, and numerous successfully simulated continuum materials.
In this work, we present a toolkit of augmented Material Point Methods for robustly and efficiently simulating material fracture both through damage modeling and through plastic softening/hardening. Our approaches are robust to a multitude of materials including those of varying structures (isotropic, transversely isotropic, orthotropic), fracture types (ductile, brittle), plastic yield surfaces, and constitutive models. The methods herein are applicable not only to the needs of computer graphics (efficiency and visual fidelity), but also to the engineering community where physical accuracy is key. Most notably, each approach has a unique set of parametric knobs available to artists and engineers alike that make them directly deployable in applications ranging from animated movie production to large-scale glacial calving simulation