Essays in decision making

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 155-168).This thesis explores the impact of individual decision making on the functioning of firms and markets. The first chapter examines how deviations from strict rationality by individuals impact the market for consumer goods. A growing body of evidence documents individual behavior that is difficult to reconcile with standard models of rational choice, and firm behavior difficult to reconcile with rational markets. In this paper I present a boundedly rational model of choice that reconciles several behavioral anomalies, and provides micro-foundational support for some puzzling empirical regularities in firm behavior. If the evaluation of an alternative is costly, individuals may find it inefficient to compare all available alternatives. Instead, when faced with an unfeasibly large choice set, some individuals may compare groups of alternatives (i.e. categories) to reduce the choice set into a more manageable set of relevant alternatives. I call these individuals categorical considerers and develop a model in which these decision makers sequentially apply a single well-behaved preference relation at different levels of aggregation. I explore the implications of this model for both individual behavior and equilibrium firm behavior in market settings. Under certain conditions, the existence of categorical considerers in a market causes firms to utilize strategies different from what would be optimal in a market of fully rational consumers. This simple model generates predictions about behavior consistent with several new field experiments, and offers possible explanations for excess spatial product differentiation, brand name premiums, and product branding.(cont.) The second chapter, written jointly with Mireille Jacobson, explores the question of what exactly not-for-profit hospitals maximize. While theories of not-for-profit hospital behavior abound, most are general statements of preferences and do not yield empirically testable (differentiable) predictions. To address this shortcoming we use a unified theoretical framework to model three popular theories of not-for profit hospital behavior: (1) "for-profits in disguise," (2) social welfare maximizers and (3) perquisite maximizers. We develop testable implications of a hospital's response to a fixed cost shock under each of these theories. We then examine the effect of a recent un-funded mandate in California that requires hospitals to retrofit or rebuild in order to comply with modern seismic safety standards. Since the majority of hospitals in the State were built between 1940 and 1970, well before a sophisticated understanding of seismic safety, a hospital's compliance cost is plausibly exogenously predetermined by its underlying geologic risk. We present evidence that within counties seismic risk is uncorrelated with a host of hospital characteristics, including ownership type. We show that hospitals with higher seismic risk experience larger increases in the category of spending that should be affected by retrofitting and that hospitals facing higher compliance costs are more likely to shut down, irrespective of ownership type. In contrast, private not-for-profits alone increase their mix of profitable services such as neonatal intensive care days and MRI minutes.(cont.) Government hospitals respond by decreasing the provision of charity care. As expected, for-profit hospitals do not change their service mix in response to this shock. These results are most consistent with the theory of not-for-profit hospitals as perquisite maximizers and allow us to reject two of the leading theories of not-for-profit hospital behavior - "for-profits in disguise" and "pure altruism." These results also imply that government owned hospitals have welfare as their maximand. More work is needed to determine the overall welfare implications of these different ownership structures. The third chapter, written jointly with Antoinette Schoar, examines the impact of individual judges on the disposition and long run success of firms seeking Chapter 11 bankruptcy protection. Using case information on Chapter 11 filings for almost 5000 private companies across five district courts in the US between 1989 and 2004, we first establish that within districts cases are assigned randomly to judges, which allows us to estimate judge specific fixed effects in their Chapter 11 rulings. We find very strong and economically significant differences across judges in the propensity to grant or deny specific motions. Specifically some judges appear to rule persistently more favorably towards creditors or debtors. Based on the judge fixed effects we created an aggregate index to measure the pro-debtor (pro-creditor) friendliness of each judge. We show that a pro-debtor bias leads to increased rates of re-filing and firm shutdown as well as lower post-bankruptcy credit ratings and lower annual sales growth up to five years after the original bankruptcy filing.by Tom Y. Chang.Ph.D

Complexity and Intermittent Turbulence in Space Plasmas

Sporadic and localized interactions of coherent structures arising from plasma resonances can be the origin of "complexity" of the coexistence of non- propagating spatiotemporal fluctuations and propagating modes in space plasmas. Numerical simulation results are presented to demonstrate the intermittent character of the non-propagating fluctuations. The technique of the dynamic renormalization-group is introduced and applied to the study of scale invariance of such type of multiscale fluctuations. We also demonstrate that the particle interactions with the intermittent turbulence can lead to the efficient energization of the plasma populations. An example related to the ion acceleration processes in the auroral zone is provided

Membrane lipid-modulated mechanism of action and non-cytotoxicity of novel fungicide aminoglycoside FG08

A novel aminoglycoside, FG08, that differs from kanamycin B only by a C8 alkyl chain at the 4″-O position, was previously reported. Unlike kanamycin B, FG08 shows broad-spectrum fungicidal but not anti-bacterial activities. To understand its specificity for fungi, the mechanism of action of FG08 was studied using intact cells of the yeast Saccharomyces cerevisiae and small unilamellar membrane vesicles. With exposure to FG08 (30 µg mL−1), 8-fold more cells were stained with fluorescein isothiocyanate, cells had 4 to 6-fold higher K+ efflux rates, and 18-fold more cells were stained with SYTOX Green in comparison to exposure to kanamycin B (30 µg mL−1). Yeast mutants with aberrant membrane sphingolipids (no sphingoid base C4 hydroxyl group, truncated very long fatty acid chain, or lacking the terminal phosphorylinositol group of mannosyl-diinositolphosphorylphytoceramide were 4 to 8-fold less susceptible to growth inhibition with FG08 and showed 2 to 10-fold lower SYTOX Green dye uptake rates than did the isogenic wild-type strain. FG08 caused leakage of pre-loaded calcein from 50% of small unilamellar vesicles with glycerophospholipid and sterol compositions that mimic the compositions of fungal plasma membranes. Less than 5 and 10% of vesicles with glycerophospholipid and sterol compositions that mimic bacterial and mammalian cell plasma membranes, respectively, showed calcein leakage. In tetrazolium dye cytotoxicity tests, mammalian cell lines NIH3T3 and C8161.9 showed FG08 toxicity at concentrations that were 10 to 20-fold higher than fungicidal minimal inhibitory concentrations. It is concluded that FG08’s growth inhibitory specificity for fungi lie in plasma membrane permeability changes involving mechanisms that are modulated by membrane lipid composition

Subcutaneous administration of TC007 reduces disease severity in an animal model of SMA

Background Spinal Muscular Atrophy (SMA) is the leading genetic cause of infantile death. It is caused by the loss of functional Survival Motor Neuron 1 (SMN1). There is a nearly identical copy gene, SMN2, but it is unable to rescue from disease due to an alternative splicing event that excises a necessary exon (exon 7) from the majority of SMN2-derived transcripts. While SMNΔ7 protein has severely reduced functionality, the exon 7 sequences may not be specifically required for all activities. Therefore, aminoglycoside antibiotics previously shown to suppress stop codon recognition and promote translation read-through have been examined to increase the length of the SMNΔ7 C-terminus. Results Here we demonstrate that subcutaneous-administration of a read-through inducing compound (TC007) to an intermediate SMA model (Smn-/-; SMN2+/+; SMNΔ7) had beneficial effects on muscle fiber size and gross motor function. Conclusion Delivery of the read-through inducing compound TC007 reduces the disease-associated phenotype in SMA mice, however, does not significantly extend survival

ROMA (Rank-Ordered Multifractal Analysis) for intermittent fluctuations with global crossover behavior

Rank-Ordered Multifractal Analysis (ROMA), a recently developed technique that combines the ideas of parametric rank ordering and one parameter scaling of monofractals, has the capabilities of deciphering the multifractal characteristics of intermittent fluctuations. The method allows one to understand the multifractal properties through rank-ordered scaling or non-scaling parametric variables. The idea of the ROMA technique is applied to analyze the multifractal characteristics of the auroral zone electric field fluctuations observed by SIERRA. The observed fluctuations span across contiguous multiple regimes of scales with different multifractal characteristics. We extend the ROMA technique such that it can take into account the crossover behavior -- with the possibility of collapsing probability distributions functions (PDFs) -- over these contiguous regimes.Comment: 24 pages, 18 figure

Mesobiliverdin IXα Enhances Rat Pancreatic Islet Yield and Function

The aims of this study were to produce mesobiliverdin IXα, an analog of anti-inflammatory biliverdin IXα, and to test its ability to enhance rat pancreatic islet yield for allograft transplantation into diabetic recipients. Mesobiliverdin IXα was synthesized from phycocyanobilin derived from cyanobacteria, and its identity and purity were analyzed by chromatographic and spectroscopic methods. Mesobiliverdin IXα was a substrate for human NADPH biliverdin reductase. Excised Lewis rat pancreata infused with mesobiliverdin IXα and biliverdin IXα-HCl (1–100 μM) yielded islet equivalents as high as 86.7 and 36.5%, respectively, above those from non-treated controls, and the islets showed a high degree of viability based on dithizone staining. When transplanted into livers of streptozotocin-induced diabetic rats, islets from pancreata infused with mesobiliverdin IXα lowered non-fasting blood glucose (BG) levels in 55.6% of the recipients and in 22.2% of control recipients. In intravenous glucose tolerance tests, fasting BG levels of 56 post-operative day recipients with islets from mesobiliverdin IXα infused pancreata were lower than those for controls and showed responses that indicate recovery of insulin-dependent function. In conclusion, mesobiliverdin IXα infusion of pancreata enhanced yields of functional islets capable of reversing insulin dysfunction in diabetic recipients. Since its production is scalable, mesobiliverdin IXα has clinical potential as a protectant of pancreatic islets for allograft transplantation

Iterative graph cuts for image segmentation with a nonlinear statistical shape prior

Shape-based regularization has proven to be a useful method for delineating objects within noisy images where one has prior knowledge of the shape of the targeted object. When a collection of possible shapes is available, the specification of a shape prior using kernel density estimation is a natural technique. Unfortunately, energy functionals arising from kernel density estimation are of a form that makes them impossible to directly minimize using efficient optimization algorithms such as graph cuts. Our main contribution is to show how one may recast the energy functional into a form that is minimizable iteratively and efficiently using graph cuts.Comment: Revision submitted to JMIV (02/24/13

A Multilevel Integrated Framework of Firm HR Practices, Individual Ambidexterity, and Organizational Ambidexterity

Research on strategic human resource (HR) management and organizational ambidexterity has assumed that organizational ambidexterity originates from operational managers that pursue both exploratory and exploitative activities. Yet, multilevel insights are absent about how and through which mechanisms HR practices may actually facilitate operational manager ambidexterity and how their ambidexterity may result into organizational ambidexterity. Our multisource and multilevel data from 467 operational managers and 104 senior managers within 52 firms reveals that the top-down effects of ability- and motivation-enhancing HR practices on operational manager ambidexterity are partially mediated by their role breadth self-efficacy and intrinsic motivational orientation. Furthermore, we find that the bottom-up relationship between operational manager and organizational ambidexterity is contingent on firm opportunity-enhancing HR practices. With that, our study provides important new multilevel insights into the effectiveness of strategic HR systems in supporting individual and organizational ambidexterity

Identification and validation of clinical predictors for the risk of neurological involvement in children with hand, foot, and mouth disease in Sarawak

Background: Human enterovirus 71 (HEV71) can cause Hand, foot, and mouth disease (HFMD) with neurological complications, which may rapidly progress to fulminant cardiorespiratory failure, and death. Early recognition of children at risk is the key to reduce acute mortality and morbidity. Methods: We examined data collected through a prospective clinical study of HFMD conducted between 2000 and 2006 that included 3 distinct outbreaks of HEV71 to identify risk factors associated with neurological involvement in children with HFMD. Results: Total duration of fever ≥ 3 days, peak temperature ≥ 38.5°C and history of lethargy were identified as independent risk factors for neurological involvement (evident by CSF pleocytosis) in the analysis of 725 children admitted during the first phase of the study. When they were validated in the second phase of the study, two or more (≥ 2) risk factors were present in 162 (65%) of 250 children with CSF pleocytosis compared with 56 (30%) of 186 children with no CSF pleocytosis (OR 4.27, 95% CI2.79–6.56, p < 0.0001). The usefulness of the three risk factors in identifying children with CSF pleocytosis on hospital admission during the second phase of the study was also tested. Peak temperature ≥ 38.5°C and history of lethargy had the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 28%(48/174), 89%(125/140), 76%(48/63) and 50%(125/251), respectively in predicting CSF pleocytosis in children that were seen within the first 2 days of febrile illness. For those presented on the 3rd or later day of febrile illness, the sensitivity, specificity, PPV and NPV of ≥ 2 risk factors predictive of CSF pleocytosis were 75%(57/ 76), 59%(27/46), 75%(57/76) and 59%(27/46), respectively. Conclusion: Three readily elicited clinical risk factors were identified to help detect children at risk of neurological involvement. These risk factors may serve as a guide to clinicians to decide the need for hospitalization and further investigation, including cerebrospinal fluid examination, and close monitoring for disease progression in children with HFMD

GALEX Ultraviolet Photometry of Globular Clusters in M31

We present ultraviolet photometry for globular clusters (GCs) in M31 from 15 square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect 200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750 Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses, respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV, to an approximate limiting V magnitude of 19. Out of six clusters with [Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore, we find no candidate metal-rich clusters with significant FUV flux, because of the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC 6441, which are metal-rich Galactic GCs with hot HB stars. We show that our GALEX photometry follows the general color trends established in previous UV studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in the UV and with population synthesis models, we suggest that the age range of M31 and Galactic halo GCs are similar.Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 200