341 research outputs found
Causal Inference: Additive Hazard Model for Mediation Analysis with Measurement Error and Marginal Structural Models
No full textIn epidemiologic and social science studies, researchers are often interested in understanding the causal effect from an exposure variable to an outcome variable. In this thesis, we develop two different models and methods to conduct causal inference: (1). causal mediation analysis under the additive hazards model with exposure-mediator interaction; (2). marginal structural additive hazards model. The existing literature requires accurate measurements of the mediator and the confounders, which could be infeasible in biomedical studies. Furthermore, the current identification results of causal effects under the additive hazards model do not allow for exposure-mediator interaction. In this thesis, we derive identification results of causal effects under the additive hazards model with exposure-mediator interaction. Furthermore, we propose consistent measurement error correction methods in the absence/presence of exposure-mediator interaction. In the second part of the thesis, we propose a marginal structural additive hazards model. We develop an estimation method for the marginal structural additive hazards model and apply the simulation-extrapolation (SIMEX) method to correct for the bias resulting from measurement error
Group Selection in Semiparametric and Nonparametric Accelerated Failure Time Models
No full textIn survival analysis, a number of regression models can be used to estimate the effects of covariates on the censored survival outcome. When covariates can be naturally grouped, group selection is important in these models. Motivated by the group bridge approach for variable selection in a multiple linear regression model, we consider group selection in a semiparametric accelerated failure time (AFT) model using Stute's weighted least squares and a group bridge penalty. This method is able to simultaneously carry out feature selection at both the group and within-group individual variable levels and enjoys the powerful oracle group selection property. Although the group bridge penalized approach can effectively remove unimportant groups, it cannot effectively remove unimportant variables within the important groups. To overcome this limitation, the adaptive group bridge method is proposed. We show that the adaptive group bridge method obtains the oracle property. Simulation studies indicate that the group bridge and adaptive group bridge approaches for the AFT model can correctly identify important groups and variables even with high censoring rates. A real data analysis is provided to illustrate the application of the proposed methods.
We further study a nonparametric accelerated failure time additive regression (NP-AFT-AR) model whose covariates have nonparametric effects on the survival time. The proposed model is more flexible than the linear model and can be fitted to high-dimensional censored data when some components are unknown non-linear functions. B-splines are used to approximate the nonparametric components. A group bridge penalized variable selection approach based on the inverse probability-of-censoring weighted least squares is developed to select nonparametric components. The proposed approach is able to distinguish the nonzero components from the zero components and estimate the nonzero components simultaneously. Computational algorithms and theoretical properties of the proposed method are established. Simulation studies indicate that the proposed method has satisfactory performance even with relatively high censoring rates. Two real data analyses are used to illustrate the application of the proposed method to survival data analysis
Between Hegemony and Enlightenment: Unthinking the Global North-South Divide in Sociological Knowledge Production
No full text181 pagesThis dissertation comprises three chapters that foreground, reconceptualize, and empirically examine the uneven global landscape of social science. Chapter 1 begins with a cross-disciplinary literature review and proposes a sociology of global academic inequalities as a research program. I characterize current scholarship as a “fruitful chaos”—rich in insights into multifaceted global knowledge production disparities but fragmented and marginal within mainstream academic discourses. I argue for sociology as an ideal disciplinary anchor for this research topic, given other disciplines’ reliance on sociological literatures, this research area’s connection to core sociological concerns, its potential to illuminate disciplinary differences, and the importance of reflexive sociology for credible knowledge making. Building on and expanding Chapter 1, Chapter 2 aims at a theoretical overhaul regarding global academic hierarchies. Distinct from the traditional focus on top-down exclusions from Anglo-American countries and static Global North-South disparities, I advance a relational and dynamic approach. This perspective underscores the agential roles of all countries—particularly peripheral ones—in shaping these hierarchies and the evolving status of a country’s rank as it fulfills conditions for intellectual ascendancy. Historical accounts of American sociology from 1860 to 1950 show its initial stagnation, post-1910s indigenous growth and eventual post-WWII global preeminence. Statistical analyses of texts published in flagship Chinese-medium sociology journals between 1980 and 2021 reveal higher valuations of Anglo-American versus local scholarship, well as a flattening of English-language advantages overtime. Chapter 3 uses mixed methods and Chinese-English bilingual sources to scrutinize two parallel strands pertaining to non-Western sociology: postcolonial sociology led by First World-based Anglophone scholars and national sociological development primarily authored by Global South-based sociologists. The analyses uncover an “exclusion paradox”: postcolonial sociology not only overshadows local traditions in mainstream visibility; it also contrasts with the latter regarding moral and epistemic standpoints. While postcolonialism centers on anti-Eurocentrism critiques and grievance, local scholars often acknowledge their “backward” status and emphasize “self-improvement” through Western learning, precisely shaped by their past encounters with Western imperialism and colonialism. This chapter highlights how perspectives from the Global South expand sociological imagination and pave pathways for an integrative future that bridges Western and non-Western sociologies
Effects of NaCl and pH on 2-hydroxypropyl-beta-cyclodextrin inclusion with oleanolic acid
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Context Matters. Raising children with a serious condition can sometimes take a toll on a mother’s long-term physical health.
No full textThis study examined how three dimensions of parenting intensity shaped physical health among mothers who care for a child with a serious condition. Fixed-effects modeling of panel data showed all three dimensions predicted poorer health over time. Associations were weaker when mothers had higher incomes or worked for pay.Population Research Cente
An integrated exposure assessment of phthalates for the general population in China based on both exposure scenario and biomonitoring estimation approaches
No full textThe representativeness of available studies on integrated exposure assessment of phthalates for the general population in China is lacking. Based on an exhaustive review of the extensive monitoring data available for China, this study presents a large-scale estimation of exposure levels to three typical phthalates, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP) and diisobutyl phthalate (DiBP), by applying both exposure scenario and biomonitoring estimation approaches. The respective median exposure levels from the exposure scenario and biomonitoring estimation approaches were 3.80, 3.02 and 1.00 mu g/kg bw/day and 3.38, 3.21 and 3.32 mu g/kg bw/day for DEHP, DBP and DiBP, which are acceptable levels of exposure with respect to current international guidelines. Evaluation results from the two approaches showed both similarities and differences among the different phthalates, making the exposure assessment comparable and more comprehensive. In terms of sources of exposure, food intake was the largest contributor, while indoor air exposure had greater contribution to the estimated daily intakes (EDIs) of DiBP than that of the other phthalates. Moreover, more attention should be paid to the higher exposure levels of phthalates in several intensively industrialized and urbanized areas, and the causes of the different exposure levels in the different regions need to be further explored. (C) 2015 Elsevier Inc. All rights reserved.State Key Joint Laboratory of Environment Simulation and Pollution Control (Peking University) [13Z04ESPCP]; National Science Foundation of China [21206011]; Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions, The National Basic Research Program of China [IDHT201304084]SCI(E)[email protected]
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