Browsing by Author "Wang, Yong"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- A Differential Geometry-Based Algorithm for Solving the Minimum Hellinger Distance EstimatorD'Ambrosio, Philip (Virginia Tech, 2008-04-21)Robust estimation of statistical parameters is traditionally believed to exist in a trade space between robustness and efficiency. This thesis examines the Minimum Hellinger Distance Estimator (MHDE), which is known to have desirable robustness properties as well as desirable efficiency properties. This thesis confirms that the MHDE is simultaneously robust against outliers and asymptotically efficient in the univariate location case. Robustness results are then extended to the case of simple linear regression, where the MHDE is shown empirically to have a breakdown point of 50%. A geometric algorithm for solution of the MHDE is developed and implemented. The algorithm utilizes the Riemannian manifold properties of the statistical model to achieve an algorithmic speedup. The MHDE is then applied to an illustrative problem in power system state estimation. The power system is modeled as a structured linear regression problem via a linearized direct current model; robustness results in this context have been investigated and future research areas have been identified from both a statistical perspective as well as an algorithm design standpoint.
- The economics of the Grameen BankAmeen, Farhad (Virginia Tech, 1996-06-06)The Grameen Bank has improved the lives of several million poor people in rural Bangladesh by providing them with credit. Using an innovative group lending program, the bank has been able to recover 97% of its loans. This dissertation is an attempt to understand the intricacies of the Grameen Bank's credit program and to throw light on those features of its innovative institutional set-up that make it so successful in recovering its loans. The dissertation is divided into six chapters and organized as follows. I first describe the institutional set-up of the Grameen Bank and its group lending program. I draw on material obtained from interviews with bank staff and borrowers during a field-trip to the Konokdia branch of the bank in Patuakhali. This is followed by an economic analysis of the bank's lending program. I analyze the multifaceted role of group lending in achieving the dramatically low default rates on loans. The emphasis is on isolating the specific ways in which the incentives created by the requirement to form groups affects group composition and the incentives for peer support, peer supervision, and loan repayment. Using a formal model, I analyze the effect of one specific feature of the Grameen Bank -- "staggered disbursement" -- on the expected loan recovery rate. In a two borrower model I show that when loan disbursement is staggered, the probability of loan recovery is higher when borrowers are linked together in a group than when there is no such group interlinkage. I analyze the implications of loan staggering on borrower welfare. The dissertation also includes an empirical analysis of the determinants of loan repayment in the Grameen Bank. Using panel data collected from a sample of Grameen Bank branches by the World Bank, I perform OLS, “fixed effects” and “random effects” regressions to examine the relationship between the variation in repayment rates across Grameen Bank branches and such variables as the average loan size, the proportion of loans to women and the distance of the branch from district headquarters. The results throw light on some of the theoretical issues raised in the earlier chapters. Chapter 6 concludes the dissertation.
- Essays on imperfect information and economic growthBose, Niloy (Virginia Tech, 1995-09-18)This dissertation is a collection of essays on economic growth in the presence of asymmetric information between lenders and borrowers in the credit market. The first chapter considers an endogenous growth model where lenders and capital producing borrowers are asymmetrically informed as to the borrower’s ability to successfully operate an investment project. In contrast to the existing literature, lenders can induce self selection either by rationing a fraction of borrowers, or by using a costly screening technology, or by a mix of the two. The growth rate of the economy and the equilibrium contract’s form are mutually dependent and are determined jointly. It is shown that a decline in the screening cost (representing a more sophisticated financial sector), paradoxically, may lower output growth and that benefit of an advanced financial sector becomes evident only when a threshold level sophistication is crossed. The second chapter draws a connection between financial development and economic growth in a neoclassical growth model. It is shown that at a low level of capital accumulation, lenders separates the borrowers by denying credit to a fraction of borrowers. As capital accumulates, credit market may function more like a modern credit market with less credit rationing and with an increasing number of lenders purchasing information to separate borrowers. The transition from rationing to screening results in a higher capital accumulation path and a higher steady state capital stock. The present chapter also highlights the conditions under which transition from rationing to screening regime will not occur and the economy may become trapped in a steady state with credit rationing and with a low level of capital. The third chapter of the dissertation analyzes the effect of inflation rate on the growth rate of output via its effect on the agents’ behavior in the credit market. It is shown that with inflation rate exceeding a critical level, a sharp fall in the growth rate of output takes place as the incentive to purchase information vanishes and borrowers are exclusively separated by means of credit rationing. This chapter also examines the panel data for a large group of countries for the period 1961-88, and shows that the relationship between the inflation rate and the growth rate of output closely follows the prediction of the theoretical model.
- Objectives and incentives in financial marketsLiu, Chung-shu (Virginia Tech, 1994-04-15)This dissertation is a collection of papers investigating objectives and incentives in financial markets. The first essay (Chapter 2) deals with the endogenous determination of credit history, credit-worthiness, loans and efforts by borrowers over time. A financial market with adverse selection and moral hazard is analyzed. Facing the adverse selection, lenders are not able to offer separate contracts to different types of borrowers. However, knowing borrowers' credit histories, lenders are able to assign different credit worthiness to borrowers that have different credit histories, and offer different contracts to different groups. It is shown that if borrowers' credit rating is too low, they make low effort to repay their debts. As a borrower acquires a good credit history and has his credit-rating upgraded above a certain point, it becomes worthwhile for him to choose high effort. A low quality borrower may make high effort in early periods in order to build up a good credit history and obtain better terms in the future contracts then shift back to the low effort even though his project continues to succeed when he approaches the end of his life.
- Risk Assessment in Chinese Hospitalized Patients Comparing the Padua and Caprini Scoring AlgorithmsChen, Xiaolan; Pan, Lei; Deng, Hui; Zhang, Jingyuan; Tong, Xinjie; Huang, He; Zhang, Min; He, Jianlin; Caprini, Joseph A.; Wang, Yong (2018-12)The current venous thromboembolism (VTE) guidelines recommend all patients to be assessed for the risk of VTE using risk assessment models (RAMs). The study was to evaluate the performance of the Caprini and Padua RAMs among Chinese hospitalized patients. We reviewed data from 189 patients with deep venous thrombosis (DVT) and 201 non-DVT patients. Deep venous thrombosis risk factors were obtained from all patients. The sensitivity and specificity of the Caprini and Padua scores for all patients were calculated. The receiver operating curve (ROC) and the area under the ROC curve (AUC) were used to evaluate the performance of each score. We documented that age, acute infection, prothrombin time (PT), D-dimer, erythrocyte sedimentation rate, blood platelets, and anticoagulation were significantly associated with the occurrence of DVT (P < .05). These results were true for all medical and surgical patients group (G1), as well as the analysis of medical versus surgical patients (G2). Finally, analysis of the scores in patients with and without cancer was also done (G3). The Caprini has a higher sensitivity but a lower specificity than the Padua (P < .05). Caprini has a better predictive ability for the first 2 groups (P < .05). We found Caprini and Padua scores have a similar predictive value for patients with cancer (P > .05), while Caprini has a higher predictive ability for no cancer patients in G3 than Padua (P < .05). For Chinese hospitalized patients, Caprini has a higher sensitivity but a lower specificity than Padua. Overall, Caprini RAM has a better predictive ability than Padua RAM.