While all racial/ethnic groups in the U.S. exhibited an increase in longevity during the twentieth century, inequalities in survival remain. Hispanics have the highest life expectancy at birth in the United States, non-Hispanic blacks have the lowest, and non-Hispanic whites exhibit life expectancy between the two minority groups. An overarching objective of Healthy People 2020 is to "achieve health equity, eliminate disparities, and improve the health of all groups." Yet, a similar objective based on the Healthy People 2010 campaign regarding reduction of health inequalities was clearly not met. As the population of the United States becomes increasingly diverse as a result of immigration, intermarriage, and evolving notions regarding race and ethnicity, health demographers must monitor adult survival outcomes and inequalities across racial and ethnic subpopulations. This dissertation examines current inequalities in survival among Hispanic, non-Hispanic black, and non-Hispanic white adults in the United States. Using the 1989-2006 National Health Interview Survey Linked Mortality Files and 2010 U.S. National Vital Statistics System, I contribute to the understanding of racial/ethnic survival disparities through three empirical studies: The first chapter affirms that Hispanic mortality rate and life expectancy estimates are favorable relative to blacks and whites, particularly for foreign-born Hispanics and from smoking-related causes. The second chapter shows that, in addition to their higher mean age at death, Hispanics exhibit less variability around that mean relative to non-Hispanic whites. Non-Hispanic blacks, on the other hand, have greater variability and lower life expectancy than the other two racial/ethnic groups. The lower variability among Hispanics relative to whites is largely attributable to lower incidence in cancer, suicide, and other external cause mortality, whereas the greater variability among blacks relative to whites is mainly due to greater dispersion in age at death from heart disease and the residual cause grouping. The third chapter finds that smoking initiation in childhood or adolescence contributes additional mortality risk for current heavy and light smokers relative to never smokers. Lower smoking prevalence and later initiation among foreign-born and U.S-born Hispanics account for much of their lower mortality risk relative to whites. / text

Risk managers currently seek new advances in statistical methodology to better forecast and quantify uncertainty. This thesis comprises a collection of new Bayesian models and computational methods which collectively aim to better estimate parameters and predict observables when data arise from stochastic failure processes. Such data commonly arise in reliability theory and survival analysis to predict failure times of mechanical devices, compare medical treatments, and to ultimately make well-informed risk management decisions. The collection of models proposed in this thesis advances the quality of those forecasts by providing computational modeling methodology to aid quantitative based decision makers. Through these models, a reliability expert will have the ability: to model how future decisions affect the process; to impose his prior beliefs on hazard rate shapes; to efficiently estimate parameters with MCMC methods; to incorporate exogenous information in the form of covariate data using Cox proportional hazard models; to utilize nonparametric priors for enhanced model flexibility. Managers are often forced to make decisions that affect the underlying distribution of a stochastic process. They regularly make these choices while lacking a mathematical model for how the process may itself depend significantly on their decisions. The first model proposed in this thesis provides a method to capture this decision dependency; this is used to make an optimal decision policy in the future, utilizing the interactions of the sequences of decisions. The model and method in this thesis is the first to directly estimate decision dependency in a stochastic process with the flexibility and power of the Bayesian formulation. The model parameters are estimated using an efficient Markov chain Monte Carlo technique, leading to predictive probability densities for the stochastic process. Using the posterior distributions of the random parameters in the model, a stochastic optimization program is solved to determine the sequence of decisions that minimise a cost-based objective function over a finite time horizon. The method is tested with artificial data and then used to model maintenance and failure time data from a condenser system at the South Texas Project Nuclear Operating Company (STPNOC). The second and third models proposed in this thesis offer a new way for survival analysts and reliability engineers to utilize their prior beliefs regarding the shape of hazard rate functions. Two generalizations of Weibull models have become popular recently, the exponentiated Weibull and the modified Weibull densities. The popularity of these models is largely due to the flexible hazard rate functions they can induce, such as bathtub, increasing, decreasing, and unimodal shaped hazard rates. These models are more complex than the standard Weibull, and without a Bayesian approach, one faces difficulties using traditional frequentist techniques to estimate the parameters. This thesis develops stylized families of prior distributions that should allow engineers to model their beliefs based on the context. Both models are first tested on artificial data and then compared when modeling a low pressure switch for a containment door at the STPNOC in Bay City, TX. Additionally, survival analysis is performed with these models using a famous collection of censored data about leukemia treatments. Two additional models are developed using the exponentiated and modified Weibull hazard functions as a baseline distribution to implement Cox proportional hazards models, allowing survival analysts to incorporate additional covariate information. Two nonparametric methods for estimating survival functions are compared using both simulated and real data from cancer treatment research. The quantile pyramid process is compared to Polya tree priors and is shown to have a distinct advantage due to the need for choosing a distribution upon which to center a Polya tree. The Polya tree and the quantile pyramid appear to have effectively the same accuracy when the Polya tree has a very well-informed choice of centering distribution. That is rarely the case, however, and one must conclude that the quantile pyramid process is at least as effective as Polya tree priors for modeling unknown situations. / text

published_or_final_version / Statistics and Actuarial Science / Master / Master of Philosophy

The importance of developing personalized risk prediction estimates has become increasingly evident in recent years. In general, patient populations may be heterogenous and represent a mixture of different unknown subtypes of disease. When the source of this heterogeneity and resulting subtypes of disease are unknown, accurate prediction of survival may be difficult. However, in certain disease settings the onset time of an observable intermediate event may be highly associated with these unknown subtypes of disease and thus may be useful in predicting long term survival. Throughout this dissertation, we examine an approach to incorporate intermediate event information for the prediction of long term survival: the landmark model. In Chapter 1, we use the landmark modeling framework to develop procedures to assess how a patient’s long term survival trajectory may change over time given good intermediate outcome indications along with prognosis based on baseline markers. We propose time-varying accuracy measures to quantify the predictive performance of landmark prediction rules for residual life and provide resampling-based procedures to make inference about such accuracy measures. We illustrate our proposed procedures using a breast cancer dataset. In Chapter 2, we aim to incorporate intermediate event time information for the prediction of survival. We propose a fully non-parametric procedure to incorporate intermediate event information when only a single baseline discrete covariate is available for prediction. When a continuous covariate or multiple covariates are available, we propose to incorporate intermediate event time information using a flexible varying coefficient model. To evaluate the performance of the resulting landmark prediction rule and quantify the information gained by using the intermediate event, we use robust non-parametric procedures. We illustrate these procedures using a dataset of post-dialysis patients with end-stage renal disease. In Chapter 3, we consider improving efficiency by incorporating intermediate event information in a randomized clinical trial setting. We propose a semi-nonparametric two-stage procedure to estimate survival by incorporating intermediate event information observed before the landmark time. In addition, we present a testing procedure using these resulting estimates to test for a difference in survival between two treatment groups. We illustrate these proposed procedures using an AIDS dataset.

published_or_final_version / abstract / toc / Statistics and Actuarial Science / Master / Master of Philosophy

Glioblastoma (GB) is the highest grade and most common form of primary adult brain tumors, characterized by a highly invasive cell population. GB tumors develop treatment resistance and ultimately recur; the median survival is nearly fifteen months and importantly, the invading cell population is attributed with having a decreased sensitivity to therapeutics. Thus, there remains a necessity to identify the genetic and signaling mechanisms that promote tumor spread and therapeutic resistance in order to develop new targeted treatment strategies to combat this rapidly progressive disease. TWEAK-Fn14 ligand-receptor signaling is one mechanism in GB that promotes cell invasiveness and survival, and is dependent upon the activity of multiple Rho GTPases including Rac1. Here, we show that Cdc42 is essential in Fn14-mediated Rac1 activation. We identified two guanine nucleotide exchange factors (GEFs), Ect2 and Trio, involved in the TWEAK-induced activation of Cdc42 and Rac1, respectively, as well as in the subsequent TWEAK-Fn14 directed glioma cell migration and invasion. In addition, we characterized the role of SGEF in promoting Fn14-induced Rac1 activation. SGEF, a RhoG-specific GEF, is overexpressed in GB tumors and promotes TWEAK-Fn14-mediated glioma invasion. Moreover, we characterized the correlation between SGEF expression and TMZ resistance, and defined a role for SGEF in promoting the survival of glioma cells. SGEF mRNA and protein expression are regulated by the TWEAK-Fn14 signaling axis in an NF-kB dependent manner and inhibition of SGEF expression sensitizes glioma cells to TMZ treatment. Lastly, gene expression analysis of SGEF depleted GB cells revealed altered expression of a network of DNA repair and survival genes. Thus TWEAK-Fn14 signaling through the GEF-Rho GTPase systems which include the Ect2, Trio, and SGEF activation of Cdc42 and/or Rac1 presents a pathway of attractive drug targets in glioma therapy, and SGEF signaling represents a novel target in the setting of TMZ refractory, invasive GB cells.

Η εξέλιξη των επιχειρήσεων και η ανάπτυξή τους έχει απασχολήσει από παλιά την ακαδημαϊκή κοινότητα (Gibrat 1931). Ένα εξιδεικευμένο τμήμα της βιβλιογραφίας αυτής ασχολείται με τον προσδιορισμό των παραγόντων επιβίωσης των επιχειρήσεων, που αποτελεί αντικείμενο της παρούσας διατριβής. Οι παράγοντες αυτοί μπορεί να αναφέρονται σε ίδια χαρακτηριστικά των επιχειρήσεων και του κλάδου στον οποίο ανήκουν ή και σε μακροοικονομικούς παράγοντες. Ο προαναφερθείς σκοπός επιτυγχάνεται μέσα από την ανάπτυξη των θεωρητικών υποθέσεων με βάση τις οποίες καταρτίζεται το οικονομετρικό υπόδειγμα. Το κύριο βάρος της εργασίας εστιάζεται στην ανάλυση των συνεχών υποδειγμάτων κινδύνου και το έλεγχο των υποθέσεων στα οποία βασίζονται. Ειδικότερα εξετάζεται η επίδραση της μορφής των δεδομένων και της χρονικής συνάθροισης στους εκτιμητές των εφαρμοζόμενων στην μέχρι σήμερα εμπειρική έρευνα υποδειγμάτων. Συγκρίνοντας διαφόρους τύπους διακριτών και συνεχών υποδειγμάτων κινδύνου οδηγούμεθα στο συμπέρασμα ότι τα μέχρι σήμερα εφαρμοζόμενα συνεχή υποδείγματα καταλήγουν σε μεροληπτικά αποτελέσματα. Η εφαρμογή διακριτών υποδειγμάτων κινδύνου PCE, που αποτελεί και την συνεισφορά μας στη βιβλιογραφία, περιορίζει σε σημαντικό βαθμό τα μειονεκτήματα των εφαρμοζόμενων στην εμπειρική έρευνα υποδειγμάτων. Η εφαρμογή της παραπάνω μεθοδολογίας προϋποθέτει δεδομένα τύπου longitudinal τα οποία δεν είναι συνήθως διαθέσιμα. Αυτό εξηγεί το γεγονός των περιορισμένων εμπειρικών εργασιών στο χώρο της επιβίωσης των επιχειρήσεων. Δεδομένης της δυσκολίας εξεύρεσης κατάλληλων δεδομένων η εμπειρική εφαρμογή στηρίχθηκε σε δεδομένα δημοσίων εγγραφών της ελληνικής κεφαλαιαγοράς για την περίοδο 1993-2002. Από όσο είμαστε σε θέση να γνωρίζουμε είναι η πρώτη φορά στη βιβλιογραφία που διεξάγεται παρόμοια έρευνα με ελληνικά δεδομένα δημοσίων εγγραφών. Τέλος, η διατριβή καταλήγει στην εξαγωγή των βασικών συμπερασμάτων και προτάσεων σχετικά με μελλοντική έρευνα. / Most economic phenomena are measured over long time intervals and this naturally leads us to see time as a discrete variable. More precisely, the underlying duration process occurs in continuous time, while the observed data comes in grouped form. In applied research, while firm life data are grouped into time intervals, continuous hazard models are used. The purpose of this paper is to investigate the sensitivity of regression coefficients and the coefficient duration dependence of the discrepancy between the statistical model and the data generating process.

Η αποεπένδυση αποτελεί αναπόσπαστο κομμάτι μιας διεθνικής. Αν και από πολλούς αντιμετωπίζεται ως αποτυχία της θυγατρικής, θα πρέπει πλέον να θεωρείται αποτέλεσμα της διαδικασίας διαρκούς εξέλιξης και προσαρμογής στο περιβάλλον έτσι ώστε αυτή να παραμένει κερδοφόρα και ανταγωνιστική. Οι λόγοι που οδηγούν στην αποεπένδυση είναι πολλοί. Εκτός από την οικονομική πορεία της μονάδας όπως πολλοί μπορεί να φαντάζονται ως κυρίαρχο λόγο αποεπένδυσης, υπάρχουν και στρατηγικοί λόγοι. Αξίζει να σημειωθεί ότι όσο σημαντικό κομμάτι μιας επιχείρησης αποτελούν οι επενδύσεις για την εξέλιξη και τη μεγέθυνση της, τόσο σημαντικές είναι και οι αποφάσεις αποεπένδυσης, η επιλογή της σωστής χρονικής στιγμής, η επιλογή του μοντέλου εξόδου καθώς και η επιλογή της περιοχής μεταφοράς των δραστηριοτήτων. Θα πρέπει εξάλλου πριν από κάθε μελλοντική επένδυση να μελετώνται διάφοροι παράγοντες, που έχουν να κάνουν τόσο με το εσωτερικό όσο και με το εξωτερικό περιβάλλον της επιχείρησης, έτσι ώστε να ελαχιστοποιούνται οι πιθανότητες μελλοντικής αποεπένδυσης. Ειδικά στις σημερινές συνθήκες, όπου η παρούσα παγκόσμια κρίση, η πιο βαθιά τα τελευταία χρόνια, επιτάσσει προσεκτικές στρατηγικές κινήσεις από την πλευρά των διεθνικών, το θέμα των αποεπενδύσεων είναι ζωτικής σημασίας. Όσον αφορά στη άποψη της κοινής γνώμης, οι αποεπενδύσεις αντιμετωπίζονται με καχυποψία αφού συνήθως έχουν εκτεταμένες και σοβαρές συνέπειες γι αυτούς που εμπλέκονται, ειδικά γι αυτούς που χάνουν τις δουλειές τους και για τις περιοχές που χάνουν πολύτιμες θέσεις εργασίας. Στην εργασία αυτή μελετούνται αρχικά οι έννοιες της επιβίωσης μιας θυγατρικής, της επιτυχίας και της αποτυχίας. Στη συνέχεια αναλύεται η έννοια της αποεπένδυσης, οι διάφορες θεωρητικές προσεγγίσεις στο φαινόμενο αυτό καθώς και τα διάφορα μοντέλα εξόδου μιας διεθνικής από μία αγορά. Σημαντικό κομμάτι της βιβλιογραφίας αποτελούν και διάφοροι παράγοντες και η σχέση τους με την επιβίωση και συνακόλουθα με την αποεπένδυση. Στο δεύτερο μέρος της εργασίας αυτής μελετάται η περίπτωση της πολυεθνικής της Frigoglass και αναλύονται οι σημαντικότερες αποεπένδύσεις αυτής. / Divestment is an integral part of foreign affiliates. Even though many face divestment as failure of the company, it has to be considered as a result of the continuing evolving process and its trial to adapt to the environment so as to be profitable and competitive. The reasons that lead to divestment are many. Apart from the economic situation of the affiliate as many can imagine as the prevalent reason, there are also strategic reasons. It is noticeable that as much important the decision of investing for a company is for the evolution and its growth, so important are also the decisions for divestment, the choice of the suitable timing, the exit mode and at last the place of relocation. Besides they have to be studied many factors before investing, that they have to do with the internal and external environment of the company, in order the possibilities of divesting to be minimized. Especially now, that the worldwide economic crisis, the deepest of the last years, needs careful strategic steps, the issue of divestment is of vital importance. As for the public opinion, divestments are often faced with suspicion, as they have to do with serious effects especially for those who concern, those who lose their jobs . In this paper, they are studied the concepts of the survival of the affiliate, of the success and the failure. Also, it is analyzed the phenomenon of divestment, its theoretical approaches and the different exit modes. Moreover, an important part of this study has to do with the factors of the survival and of divestment. In the second part is studied the case of the multinational Frigoglass and they are analyzed its most important cases of divestments.

Trends in Rio Grande wild turkey (Meleagris gallopavo intermedia) abundance on the Edwards Plateau (EP), Texas, have been either stable or in decline since the 1970s. Four study areas, 2 each within stable (Stable Area A, SAA; Stable Area B, SAB) and declining regions (Declining Area A, DAA; Declining Area B, DAB), were delineated to examine (1) both annual and seasonal survival, (2) relative mammalian predator mean abundance (RMA), and (3) potential effects of lunar phase on scent-station visitation. During February 2001-March 2003, 257 turkeys were captured and instrumented with radio transmitters. Survival probabilities were generated using a Kaplan-Meier product limit estimator; a log-rank test tested for differences among sites. Annual survival was statistically different between regions (stable 0.566 ± 0.081; declining 0.737 ± 0.094; X2 = 3.68, P = 0.055) in 2002. Seasonal survival differed between regions (stable 0.812 ± 0.103; declining 0.718 ± 0.130; X2 = 3.88, P = 0.049) in spring 2003. Annual survival results during 2002 were counterintuitive with turkey trend data. Scent-station transects were established on non-paved ranch roads within study regions. Scent-station indices revealed higher (H = 19.653, P ≤ 0.001) RMA of opossum (Didelphis virginiana) and skunk (eastern spotted [Spilogale putorius], striped [Mephitis mephitis], or western spotted [S. gracilis]) (SAA, x⎯ = 0.0148; SAB, x⎯ = 0.0151; DAA, x⎯ = 0.0042; DAB, x⎯ = 0.0065) on stable areas. Higher RMA of coyotes (Canis latrans) on declining areas (SAA, x⎯ = 0.0067; SAB, x⎯ = 0.0022; DAA x⎯ = 0.0234; DAB x⎯ = 0.0434) suggested a possible causative factor of the decline, but abundance indices were not verified by empirical data though. Lunar phase was not a significant (T = -0.225, P = 0.822) covariate in scent-station visits by raccoons, opossums (new, x⎯ = 0.0111; full, x⎯ = 0.0324), or unidentified tracks (new, x⎯ = 0.0649; full, x⎯ = 0.0375). Nightly precipitation and wind speed probably influence mammalian use of scent stations more so than lunar illumination.

This essay deals with different survival strategies in Hemingway´s The Sun Also Rises, with a focus on three of the characters: Jake, Brett and Cohn. They all try to survive mentally in post-war Europe, and have different ways of handling their traumas.