by Thomas M. Stoker. / "July 1983." / Bibliography: p. 27.

Thesis (Ph.D.)--Baylor University, 2009. / Includes bibliographical references (p. 255-262).

abstract: A least total area of triangle method was proposed by Teissier (1948) for fitting a straight line to data from a pair of variables without treating either variable as the dependent variable while allowing each of the variables to have measurement errors. This method is commonly called Reduced Major Axis (RMA) regression and is often used instead of Ordinary Least Squares (OLS) regression. Results for confidence intervals, hypothesis testing and asymptotic distributions of coefficient estimates in the bivariate case are reviewed. A generalization of RMA to more than two variables for fitting a plane to data is obtained by minimizing the sum of a function of the volumes obtained by drawing, from each data point, lines parallel to each coordinate axis to the fitted plane (Draper and Yang 1997; Goodman and Tofallis 2003). Generalized RMA results for the multivariate case obtained by Draper and Yang (1997) are reviewed and some investigations of multivariate RMA are given. A linear model is proposed that does not specify a dependent variable and allows for errors in the measurement of each variable. Coefficients in the model are estimated by minimization of the function of the volumes previously mentioned. Methods for obtaining coefficient estimates are discussed and simulations are used to investigate the distribution of coefficient estimates. The effects of sample size, sampling error and correlation among variables on the estimates are studied. Bootstrap methods are used to obtain confidence intervals for model coefficients. Residual analysis is considered for assessing model assumptions. Outlier and influential case diagnostics are developed and a forward selection method is proposed for subset selection of model variables. A real data example is provided that uses the methods developed. Topics for further research are discussed. / Dissertation/Thesis / Ph.D. Statistics 2012

Social disorganization and routine activity theories have been studied over the past 30 years. The subsequent research examines prior concepts that were constructed to measure these theories and recent attempts in combining these theories. It also examines how these concepts have been measured using a multitude of geographical scales. It suggests that one consistent set of geographical scales must be used and that these must be easily reproduced in order to test these concepts on a multitude of cities that have a wide variation in populations.

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Melanoma is the most lethal type of skin cancer with over 132,000 cases occurring globally each year and continually rising incidence. BRAFV600E inhibitors have led to clinically significant improvements in outcomes for melanoma patients, yet many patients with metastatic melanoma rapidly succumb to the disease due to eventual chemoresistance or insensitivity to the drug. Thus, it is critical to identify new therapies that can act alone, or be combined with available treatments for enhanced efficacy and/or to overcome drug resistance. Evidence from human melanoma indicates that the melanocyte lineage is critical for melanoma survival and contributes to therapeutic resistance. MITF is a highly conserved “master melanocyte transcription factor” with a complex role in melanoma. Our lab has previously developed a temperature sensitive BRAFV600E mitfavc7 zebrafish melanoma model carrying a human oncogene and mitfavc7 splice site mutation that enables the conditional control of its endogenous activity by changes to water temperature. As part of my PhD project, I characterized and compared two new models developed since then: a very aggressive BRAFV600E mitfavc7p53M214K melanoma model with three driving mutations and a slower developing BRAF-independent mitfavc7p53M214K. I showed that the MITF activity is crucial for melanocyte survival in both models and that both mutated BRAF and p53 deficiency are oncogenic with low levels of MITF, and result in fish nevi and melanoma resembling the pathology of human disease. Both models are also relevant to a low-MITF subclass of human melanomas that emerged from a recent classification by The Cancer Genome Atlas Network. In addition, I established that, similarly to the BRAFV600Emitfavc7, complete inhibition of MITF activity leads to rapid tumour regression, but once its activity is restored the melanomas recur at the same site as the original tumour. I used histopathology studies and melanocyte lineage transgenes to identify and visualize subpopulations of cells remaining at the site of regression in these new zebrafish melanoma models. I hypothesised that these are the cells of origin for tumour recurrence (melanoma stem or progenitor cells), showed that some of them express a cancer stem cell marker aldehyde dehydrogenase, and attempted to target these subpopulations using 5-nitrofurans (a prodrug NFN1, shown previously by our lab to target ALDHhigh subpopulations in context of melanoma) in fish after melanoma regression. Finally, I also developed and described a new primary zebrafish melanoma cell line that I derived from one of these zebrafish tumours. This study is still in progress, but the cell line will be a useful tool for further investigation of these proposed melanoma progenitor cells in vitro, with potential applications for lineage tracing and transplantations.

Building on the work of Pierce & Sweeney’s study from 2004 and their Quality Threatening Behavior-model (QTB) in conjunction with Chang & Hwang (2003), this study is an explanatory quantitative study into the determinants of audit quality. I aim to determine whether an overemphasis on customer retention can serve as determinant of audit quality. The study targeted contemporary ’Big Four’ auditors in Sweden. Data was gathered by means of a questionnaire constructed according to the QTB model as outlined by Pierce and Sweeney with the addition of a customer retention factor. Challenges involved in the study included translating the instrument employed as well as making comparisons across regional contexts. For these reasons, the study was furthermore limited to larger city firms. The conclusions of the study found that customer retention in fact could serve as a determinant of audit quality. A series of regression models, with slight alterations to account for robustness vulnerabilities, were tested, all of which pointed towards similar results: that customer retention indeed could constitute a material improvement to the QTB model. A closer investigation confirmed that these results are significant, and that the vulnerabilities feared were either contained or within tolerable range in the final model. An unexpected finding in the study was the very high explanatory power of the model derived and the small differences generated by the shift in cultural context. The high explanatory value is primarily attributed to the model already having high explanatory value as well as the questionnaire being very clear-cut. The small impact of cultural differences is explained by the fact that the Big Four are global firms and there is a large degree of mobility within the firms hence they are relatively homogenous. Ultimately, no final conclusions should be drawn, yet since the results are so strong one can begin to suspect that customer retention indeed does matter to audit quality. Hence, the author recommends further studies on this topic.