Browsing by Subject "Heterogeneity"

In this dissertation, I study how individual households respond to unanticipated changes in income. I focus on two recent fiscal programs, the Economic Stimulus Act (ESA) of 2008 and the Coronavirus Aid, Relief, and Economic Security (CARES) Act of 2020.

In the first chapter, I study the ESA. I demonstrate when Economic Stimulus Payments were being distributed to households, the macroeconomic environment was characterized by three main facts: (1) household income had yet to fall, (2) households were anticipating worsening economic conditions, and (3) consumer credit markets were already tightening. I modify the standard Permanent Income Hypothesis consumption-saving model to incorporate these three facts and assess the model's prediction for the household response to unanticipated income in the form of Economic Stimulus Payments. This modified model predicts that borrowing constrained households that receive the stimulus wish to increase consumption, but are forced to deleverage. Depending on the degree of indebtedness, size of the stimulus and recession, and size of the credit crunch, households may either increase or decrease consumption. Using micro-level household data from the Survey of Income and Program Participation, I find that consistent with the Permanent Income Hypothesis model, changes in behavior are most sensitive for households near their borrowing constraint. The empirical results suggest that constrained households used most of the stimulus to deleverage, but also increased spending. The more indebted is a household, the more likely it is to use the stimulus to repay debt, and the less likely it is to increase consumption or savings. This is inconsistent with the standard model but is consistent with the model incorporating the full macroeconomic environment in 2008.

In the second chapter, I study the CARES Act. As part of the Act, the IRS distributed $300 billion in Economic Impact Payments (EIPs) directly to US households. In the Census Bureau's Household Pulse Survey, almost 75% of households receiving an EIP reported using it to mostly pay for expenses. Separating respondents based on labor income interruptions, 84% of unemployed households reported mostly spending their EIPs, compared to 63% of employed households. I contribute to studying the trade-off between the timeliness and specificity of government transfer programs. Since the consumption responses for employed and unemployed households are similar, I conclude that a more targeted program at the expense of timeliness may not have have had a larger aggregate spending response. I find larger differences between households sorted on income, regardless of employment status, suggesting that income may be the more important determinant of EIP usage. Overall, I conclude that Economic Impact Payments played an important role in stabilizing aggregate spending.

In the final chapter, I build and estimate a quantitative model that generates a distribution of consumption responses similar to those observed in the data. I build and estimate a quantitative model of bounded rationality consistent with two motivating facts. First, highly liquid households have large consumption responses out of income shocks that cannot be driven by borrowing constraints. Second, larger income shocks induce smaller consumption responses and more intertemporal smoothing. In the model, a household responds to an income shock by reoptimizing over a planning horizon chosen to trade off benefits of consumption smoothing against cognitive planning costs. The optimal planning horizon is increasing in income, wealth, and the magnitude of the income shock. Estimated using the Economic Stimulus Act of 2008, the model implies that fiscal policies targeting more households with smaller payments induce less intertemporal smoothing and have the largest aggregate spending impact.

I develop and justify a measure of polarization based on pairwise differences between and within groups, which improves on previous approaches in its ability to account for multiple dimensions and an arbitrary number of partitions. I apply this measure to a roll-call based ideological mapping of U.S. legislators to show that while the contemporary Congress is polarized relative to mid-century levels, the current state is not historically unprecedented.

I then estimate the ideology of public opinion using survey respondent thermometer evaluations of political elites and population subgroups. I find that party affiliation is polarizing in this space, but that alternate partitions of the electorate, along racial, educational, and other socio-demographic lines, are de-polarized.

Finally, I estimate a two-dimensional latent space based on social identity trait co-occurrence. I show that positions in this space are predictive of survey respondent ideology, partisanship, and voting behavior. Further, I show that when conceived in this way, we do observe a polarization of the social space over the last half-century of American politics.

Glioblastoma (GBM) is the most common and deadly primary malignant brain tumor with a median survival of <20 months. Despite aggressive standard of care therapies, GBM remains lethal. Alternatively, immunotherapy in the form of adoptively transferred T cells expressing chimeric antigen receptors (CARs) has emerged as a promising approach to targeting brain tumors. Preclinically, CARs for GBM-specific epidermal growth factor receptor variant III (EGFRvIII; CARvIII) have been successful combined with total body irradiation (TBI) in treating tumors exclusively expressing EGFRvIII. While effective at the bench, this model does not translate clinically; therefore, next generation immunotherapy aims to enhance CARs to secrete immunomodulatory factors to better treat GBM. This work spans the development and success of this new CAR “armored” to secrete IL-12, a stimulatory cytokine that enhances T cell persistence and function, to treat orthotopic heterogeneous GBM.Chapters 1 and 2 provide an overview of GBM. Detailed in these chapters are the current clinical standard of care, immune privilege of the brain, and various immunotherapies under active preclinical and clinical investigation. Chapter 3 details the history of adoptive T cell therapy in the context of brain tumors. Specifically, it focuses on existing CAR T cell therapies for GBM. Chapter 4 summarizes the next generation of “armored” CARs currently being developed. In Chapter 5 we present the development of a new CAR T therapy and demonstrate, for the first time, its efficacy in treating an in vivo, heterogeneous brain tumor. Chapter 6 summarizes the data gathered from our single-cell sequencing of immune cells collected from CAR-treated, tumor-bearing brains and flow cytometry. Additionally, we briefly evaluated the toxicity of our CAR treatment. In Chapter 7, we evaluate numerous in vivo, immunological depletion models to better understand the mechanism of action of our CAR therapy. To conclude, Chapter 8 contains closing remarks on the current state of CAR T cell therapy and future directions. To summarize, we have engineered a fourth-generation CAR T cell that can cure homogeneous and kill heterogeneous brain tumors in immunocompetent mice without host lymphodepletive preconditioning through reprogramming endogenous immune cells in the tumor microenvironment.

Secession is a watershed event not only for the new state that is created and the old state that is dissolved, but also for neighboring states, proximate ethno-political groups and major powers. This project examines the problem of violent secessionist conflict and addresses an important debate at the intersection of comparative and international politics about the conditions under which secession is a peaceful solution to ethnic conflict. It demonstrates that secession is rarely a solution to ethnic conflict, does not assure the protection of remaining minorities and produces new forms of violence. To explain why some secessions produce peace, while others generate violence, the project develops a theoretical model of the conditions that produce internally coherent, stable and peaceful post-secessionist states rather than recursive secession (i.e., secession from a new secessionist state) or interstate disputes between the rump and secessionist state. Theoretically, the analysis reveals a curvilinear relationship between ethno-territorial heterogeneity and conflict, explains disparate findings in the literature on ethnic conflict and conclusively links ethnic structure and violence. The project also contributes to the literature on secessionist violence, and civil war more generally, by linking intrastate and interstate causes, showing that what is frequently thought of as a domestic phenomenon is in fact mostly a phenomenon of international politics. Drawing upon original data, methodological advances at the interface of statistics, computer science and probability theory, and qualitative methods such as elite interviews and archival research, the project offers a comprehensive, comparative and contextual treatment of secession and violence.