Essays on Testing Hypotheses When Non-stationarity Exists in Panel Data Models

This dissertation consists of two essays on testing hypotheses in panel data models when non-stationarity exists in the model. This is done under the high-dimensional framework where both n (cross-section dimension) and T (time series dimension) are large. In the first essay, I discuss the limiting distribution of the t-statistic; using different panel data estimators and propose using the t-statistic based on Feasible GLS estimator. In the second essay, I develop the bootstrap F-statistic for cross-sectional independence in a panel data model with factor structure. The first essay considers the problem of hypotheses testing in a simple panel data regression model with random individual effects and serially correlated disturbances. Following Baltagi, Kao and Liu (2008), I allow for the possibility of non-stationarity in the regressor and/or the disturbance term. While Baltagi et al. (2008) focus on the asymptotic properties and distributions of the standard panel data estimators, this essay focuses on test of hypotheses in this setting. One important finding, is that unlike the time series case, one does not necessarily need to rely on the super-efficient type AR estimator by Perron and Yabu (2009) to make inference in panel data. In fact, I show that the simple t-ratio always converges to the standard normal distribution regardless of whether the disturbances and/or the regressor are stationary. One caveat is that this may not be robust to heteroskedasticity of the error terms, but it is robust to heterogenous AR parameters across individuals. The Monte Carlo simulations in support of all the results are also provided in this essay. The second essay discusses testing hypotheses of cross-sectional dependence in a panel data model with an introduction of factor structure. Following Bai (2003, 2004, 2009) and Bai, Kao and Ng (2009), I again allow for the possibility of non-stationarity in the regressor and the factor. I give attention to test of hypotheses using F-tests in this setting. The limiting distribution of F-statistics under the high-dimensional framework has not been derived yet in the literature perhaps because of its theoretical complexity. To circumvent this difficulty, this essay suggests the use of wild bootstrap F-tests based on simulation results under various cases where both regressors and factors can be stationary or non-stationary. The Monte Carlo results show that the bootstrap F-tests perform well in testing cross-sectional independence and are recommended in practice. They have the advantage of being feasible even when we do not observe the factors and do not require for formal theoretical approximations. It is also shown that the bootstrap F-tests are robust to heteroskedasticity but sensitive to serial correlation

Inflammatory myofibroblastic tumor of the pleura with adjacent chest wall invasion and metastasis to the kidney: a case report

Abstract Background Inflammatory myofibroblastic tumor is a rare benign neoplasm that frequently involves the lung and abdominopelvic region, and is found mainly in children and young adults. Inflammatory myofibroblastic tumor tends to be locally invasive or recurrent, and rarely metastasizes. Case presentation A 76-year-old Korean man presented with a history of upper back pain for 2 months and motor weakness in both lower extremities for 2 days. Contrast-enhanced computed tomography of his chest and abdomen showed a large heterogeneous pleural mass involving the right fifth rib and vertebral body and a mass infiltrating the right renal hilum. Computed tomography-guided percutaneous needle biopsy of the pleural mass was performed. The histological findings on hematoxylin and eosin staining showed proliferation of spindle cells with infiltration of lymphocytes and plasma cells. Immunohistochemistry showed neoplastic cells positive for CD68, focally positive for smooth muscle actin, and negative for cytokeratin and desmin. Inflammatory myofibroblastic tumor was diagnosed based on the histological examination. Treatment with glucocorticoids (methylprednisolone 1 mg/kg) and radiotherapy (5 days/week for 3 weeks at 3 Gy/fraction, 45 Gy/15 days) was started. After 1 month, chest computed tomography showed a reduction in the size of the pleural mass, and abdominopelvic computed tomography showed decreased infiltration around the right renal pelvis. Conclusions Inflammatory myofibroblastic tumor is a rare neoplasm of intermediate malignant potential due to a tendency for local recurrence and it rarely develops distant metastases. Complete surgical resection is the primary treatment. However, unresectable and metastatic inflammatory myofibroblastic tumor can be treated with systemic therapy, including glucocorticoids, radiotherapy, and/or chemotherapy

Survival Analysis after Living Donor Liver Transplantation for Hepatocellular Carcinoma: A Single Center Cohort Study

Background: Living-donor liver transplantation (LDLT) for hepatocellular carcinoma (HCC) has been used as a curative treatment option for hepatocellular carcinoma (HCC) because of a shortage of deceased donors. This study aimed to investigate survival outcomes after LDLT for HCC. Method: This study included 359 patients undergoing LDLT for HCC. We analyzed overall survival (OS) and recurrence-free survival (RFS) and the prognostic factors related to them. Results: The 5-year OS and RFS rates of patients within the Milan criteria (WM) were better than those of patients beyond the Milan criteria (BM) (87.3% vs. 64.1% and 87.6% vs. 57.8%, respectively, both p < 0.05). Alpha-fetoprotein level (AFP) > 400 ng/mL (hazard ratio (HR), 2.07; 95% CI, 1.28–3.36; p < 0.05) and HCC of BM (HR, 2.61; 95% CI, 1.60–4.26; p < 0.05) at immediate pretransplant were independent risk factors of OS. AFP > 400 ng/mL (HR, 2.16; 95% CI, 1.34–3.49; p < 0.05) and HCC of BM (HR, 3.01; 95% CI, 1.81–5.01; p < 0.05) were also independent risk factors of RFS. In pathologic findings of explanted liver, tumor size, Edmondson–Steiner grade III–IV, and microvascular invasion were independent risk factors of both OS and RFS (p < 0.05). Conclusions: BM and AFP > 400 ng/mL at immediate pretransplant are unfavorable predictors of survival outcomes after LDLT for HCC

Identification of the Vibrio vulnificus wbpP Gene and Evaluation of Its Role in Virulence

A wbpP gene encoding a putative UDP-N-acetyl-d-glucosamine C(4) epimerase was identified and cloned from Vibrio vulnificus. The functions of the wbpP gene, assessed by the construction of an isogenic mutant and by evaluating its phenotype changes, demonstrated that WbpP is essential in both the pathogenesis and the capsular polysaccharide biosynthesis of V. vulnificus