Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 178-188).

Orientador: Antonio Carlos Pereira / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-14T03:33:33Z (GMT). No. of bitstreams: 1 Oliveira_JulianaGobbode_M.pdf: 947660 bytes, checksum: 6fdaad170a78d94e585a32986b75b455 (MD5) Previous issue date: 2008 / Resumo: O objetivo do presente estudo foi avaliar, por meio de um modelo de análise de sobrevivência, a retenção do selante ionomérico modificado por resina (Vitremer®) aplicado sobre as superfícies oclusais dos primeiros molares permanentes de escolares de 6 a 8 anos de idade em Piracicaba, SP. Os escolares foram selecionados por meio de exame prévio e de acordo com o risco individual, por uma única examinadora, calibrada e seguindo as recomendações da OMS para a cárie dentária e adicionalmente, foi feita a inclusão de lesões iniciais ativas (LI). Foram incluídos os indivíduos que apresentaram ao menos dois primeiros molares permanentes hígidos, num total de 93 escolares provenientes de duas escolas municipais e alocados em dois grupos de acordo com o risco individual - Grupo (AS) - alto risco selante (n= 57) e aqueles com ceod e CPOD=0 pertenceram ao Grupo (BS) - baixo risco selante (n=52). A aplicação do selante ionomérico (Vitremer®) nas superfícies oclusais dos primeiros molares permanentes hígidos foi realizada em ambiente clínico e as avaliações e realizadas a cada seis meses por uma examinadora calibrada. Um modelo de análise de Sobrevivência (método de Kaplan-Meier) estimou as probabilidades de sobrevivência do selante na superfície oclusal (tempo para a perda total do selante). Aos 18 meses de acompanhamento os grupos AS e BS apresentaram 8 e 6 selantes com perda total do material, respectivamente, correspondendo a 4,1% de perda para os de alto risco e 3,1% para os de baixo risco. Em relação à perda parcial, observou-se aos 18 meses 11,7% e 9,3% para os grupos AS e BS, respectivamente. Não houve diferença entre os grupos quanto à sobrevivência do selante. Conclui-se que o selante ionomérico modificado por resina (Vitremer®) é satisfatório quanto à retenção, após 18 meses de avaliação e sugere-se estudos longitudinais mais extensos para averiguar essa retenção ao longo do tempo. / Abstract: The objective of the present study was to evaluate, by an analysis surviving model, the retencion of ionomeric sealer modified by resin (Vitremer), applied on oclusal surface of permanent molar teeth of children of age range 6-8 years on schools of Piracicaba city, SP. Children were selected by a previus exam and according to individual riscs, by only one evaluator, blinded and following the recomendations of WHO (World Health Organization) to cavities and additionally, included the initial cavities lesion. Patients who had at least two permanent molars with no cavities were included. Ninetythree students from two schools were recruted and divided according to individual riscs into the following groups: Group (HS) - high level sealer (n=57) and Group (LS) - low level sealer (n=52) whose teeth had "dmf" and DMFT = 0. The ionomeric sealer (Vitremer®) was applied in a clinical procedure on teeth with no cavities. Evaluation was done at every six months by an evaluator. An analysis surviving model (Kaplan-Meier method) evaluated the loss of the sealer from oclusal surface of the teeth. After 18 months groups HS and LS demonstrated 8 and 6 total loss of sealer, respecitvely. The percentage of lost were 4,1% to high level and 3,1% to low level. According to partial loss, after 18 months the percentage presented to HS was 11,7% and 9,3% to LS. There was no statistically significant difference between the two treatment groups from surviving sealer. The evaluation of the groups led to a conclusion that ionomeric sealer (Vitremer®) is very satisfatory on retencion after 18 months evaluation. Further research is required to determine the effectiviness and efficiency of sealer activity. / Mestrado / Odontologia em Saude Coletiva / Mestre Profissional em Odontologia em Saúde Coletiva

The aim of the research is the statistical modelling of parametric survival distributions of grouped survival data of long- and shortterm policies in the insurance industry, by means of a method of maximum likelihood estimation subject to constraints. This methodology leads to explicit expressions for the estimates of the parameters, as well as for approximated variances and covariances of the estimates, which gives exact maximum likelihood estimates of the parameters. This makes direct extension to more complex designs feasible. The statistical modelling offers parametric models for survival distributions, in contrast with non-parametric models that are used commonly in the actuarial profession. When the parametric models provide a good fit to data, they tend to give more precise estimates of the quantities of interest such as odds ratios, hazard ratios or median lifetimes. These estimates form the statistical foundation for scientific decisionmaking with respect to actuarial design, maintenance and marketing of insurance policies. Although the methodology in this thesis is developed specifically for the insurance industry, it may be applied in the normal context of research and scientific decision making, that includes for example survival distributions for the medical, biological, engineering, econometric and sociological sciences. / Dissertation (PhD (Mathematical Statistics))--University of Pretoria, 2002. / Mathematics and Applied Mathematics / unrestricted

Indiana University-Purdue University Indianapolis (IUPUI) / Background: High blood pressure (HBP) is a common risk factor for dementia in elder population. Anti-hypertensive medications have been reported to associate with lower incidence rate of dementia in elder African Americans. The Apolipoprotein E (ApoE) epsilon 4 allele has been shown to be associated with both increased dementia and hypertension risk. However, previous studies had not examined the association between anti-hypertensive medications by ApoE status accounting for the competing risk from death. Methods: This is a prospective observational cohort study in 1236 community-dwelling hypertensive African Americans aged 65 years and older without dementia at baseline, with follow-up cognitive assessment and clinical evaluation for dementia diagnosis. Dementia-free mortality was considered as the competing risk. Of these, 707 participants were genotyped for ApoE status. Anti-hypertensive medication use was obtained from prescription records in the electronic medical records of the Indiana Network for Patient Care (INPC). Cox proportional cause-specific hazard (CSH) regression models were applied to assess the association between anti-hypertensive medication use and CSHs for dementia and death in ApoE epsilon 4 carriers and non-carriers separately. Key results: In ApoE epsilon 4 carriers, participants using anti-hypertensive medications had lower CSH of dementia compared to those not on anti-hypertensive medications before adjusting for blood pressure (BP) (hazard ratio (HR), 0.365; 95% CI, 0.170 – 0.785; p = 0.0099). The HR was no longer significant once BP control was adjusted (HR, 0.784; 95% CI, 0.197 – 3.123; p = 0.7303). Anti-hypertensive medications were not associated with dementia rate in non-carriers. In ApoE epsilon 4 non-carriers, participants on anti-hypertensive treatment showed significantly lower CSH of death compared to those not on mediations adjusting for covariates and BP control (HR, 0.237; 95% CI, 0.149 – 0.375; p < 0.0001). There was no significant association between anti-hypertensive medication use and death in ApoE epsilon 4 carriers. Conclusions: Anti-hypertensive medication was associated with lower dementia rate in ApoE epsilon 4 carriers and that rate was primarily mediated through BP control. In non-carriers, anti-hypertensive medication was significantly associated with lower mortality rate and this association appears to be independent of BP control.

Many observational studies assessing the effects of treatments or exposures are limited to comparisons between treatment users and nonusers or exposed and unexposed participants at study entry. However, the underlying and etiologically relevant exposure may gradually increase over time before reaching some plateau. This amount of time required for this latent cumulative exposure to reach a maximum hazard will be referred to as the "lag", coming from the concept that the association between exposure and outcome is lagged or delayed. Accounting for the lag is essential when analyzing exposure-response associations adequately. My challenge was to simultaneously estimate the lag-time and the exposure's lagged-association with the outcome at plateau. In this dissertation, I draw an analogy with the pharmacokinetic one-compartment model (OCM). OCM describes the accumulation of a medication in the body based on an exponential cumulative density function whose rate of increase is defined by a half-life parameter. Upon discontinuation, the OCM assumes that a medication will eliminate at the same half-life rate. The decline, for my purposes, can be interpreted as the time to return to a null effect of exposure, which occurs at roughly 4-5 half-lives. My methods model the association of a latent exposure and dichotomous outcome using a half-life of effect, similar to the OCM, in longitudinal analyses of single and repeated exposures. I derive profile likelihood-based algorithms to estimate of the upper limit of association simultaneously with the rate of latent exposure growth towards or away from plateau. Lastly, I extend this approach to allow different half-life parameters for incline and decline. Using simulations, I analyze the performance of my approach by comparing bias and coverage of the estimates for the half-life and effect parameters. With data from the Black Women's Health Study Cohort (a prospective cohort of 59,000 women followed 1995-2015), I show that prolonged cigarette smoking is associated with a maximum hazard of cardiovascular disease (CVD) at 2.5 times the hazard of never smokers. Additionally, I estimate that it takes about 7 years of smoking cessation for an individual's hazard of CVD to decrease by 50%. / 2020-11-13T00:00:00Z

The objective of the current work is to develop novel procedures for the analysis of functional data and apply them for investigation of gender disparity in survival of lung cancer patients. In particular, we use the time-dependent Cox proportional hazards model where the clinical information is incorporated via time-independent covariates, and the current age is modeled using its expansion over wavelet basis functions. We developed computer algorithms and applied them to the data set which is derived from Florida Cancer Data depository data set (all personal information which allows to identify patients was eliminated). We also studied the problem of estimation of a continuous matrix-variate function of low rank. We have constructed an estimator of such function using its basis expansion and subsequent solution of an optimization problem with the Schattennorm penalty. We derive an oracle inequality for the constructed estimator, study its properties via simulations and apply the procedure to analysis of Dynamic Contrast medical imaging data.

There has been confusion in choosing a proper survival model between two popular survival models of discrete and continuous survival analysis. This study aimed to provide empirical outcomes of two survival models in educational contexts and suggest a guideline for researchers who should adopt a suitable survival model. For the model specification, the study paid attention to three factors of time metrics, censoring proportions, and sample sizes. To arrive at comprehensive understanding of the three factors, the study investigated the separate and combined effect of these factors. Furthermore, to understand the interaction mechanism of those factors, this study examined the role of the factors to determine hazard rates which have been known to cause the discrepancies between discrete and continuous survival models. To provide empirical evidence from different combinations of the factors in the use of survival analysis, this study built a series of discrete and continuous survival models using secondary data and simulated data. In the first study, using empirical data from the National Longitudinal Survey of Youth 1997 (NLSY97), this study compared analyses results from the two models having different sizes of time metrics. In the second study, by having various specifications with combination of two other factors of censoring proportions and sample sizes, this study simulated datasets to build two models and compared the analysis results. The major finding of the study is that discrete models are recommended in the conditions of large units of time metrics, low censoring proportion, or small sample sizes. Particularly, discrete model produced better outcomes for conditions with low censoring proportion (20%) and small number (i.e., four) of large time metrics (i.e., year) regardless of sample sizes. Close examination of those conditions of time metrics, censoring proportion, and sample sizes showed that the conditions resulted into high hazards (i.e., 0.20). In conclusion, to determine a proper model, it is recommended to examine hazards of each of the time units with the specific factors of time metrics, censoring proportion and sample sizes. / Ph. D.

New agricultural technologies can improve productivity to meet the increased demand for food that places pressure on agricultural production systems in developing countries. Because technological innovation is one of major factors shaping agriculture in both developing and developed countries, it is important to identify factors that help or that hinder the adoption process. Adoption analysis can assist policy makers in making informed decisions about dissemination of technologies that are under consideration. It is also important to estimate the impact of a technology. This dissertation contains three essays that estimate factors affecting integrated pest management (IPM) adoption and the impact of IPM on sweet gourd farming in Bangladesh. The first essay estimates factors that affect the timing of IPM adoption in Bangladesh. It employs duration models, fully parametric and semiparametric, and (i) compares results from different estimation methods to provide the best model for the data, and (ii) identifies factors that affect the length of time before Bangladeshi farmers adopt an agricultural technology. The paper provides two conclusions: 1) even though the non-parametric estimate of the hazard function indicated a non-monotone model such as log-normal or log-logistic, no differences are found in the sign and significance of the estimated coefficients between the non-monotone and monotone models. 2) economic factors do not directly influence the adoption decision but rather factors related to information diffusion and farmer's non-economic characteristics such as age and education. Particularly, farmer's age and education, membership in an association, training, distance of the farmer's house from local and town markets, and farmer's perception about the use of IPM affect the length of time to adoption. Farm size is the only variable closely related to economic factors that is found to be significant and it decreases the length of time to adoption. The second paper measures Bangladeshi farmers' attitudes toward risk and ambiguity using experimental data. In different sessions, the experiment allows farmers to make decisions alone and communicate with peers in groups of 3 and 6 to see how social exchanges among peers affect attitudes toward uncertainty. Combining the measured attributes to household survey data, the paper investigates the factors affecting those attributes as well as the role of risk aversion and ambiguity aversion in technology choice by farmers who: face uncertainty alone, in a group of 3, or in a group of 6. It finds that Bangladeshi farmers in the sample are mostly risk and ambiguity averse. Their risk and ambiguity aversion, moreover, differ when they face the uncertain prospects alone from when they can communicate with other peer farmers before making decisions. In addition, farmer's demographic characteristics affect both risk and ambiguity aversion. Finally, findings suggest that the roles of risk and ambiguity aversion in technology adoption depend on which measure of uncertainty behavior is incorporated in the adoption model. While risk aversion increases the likelihood of technology adoption when farmers face uncertainty alone, only ambiguity aversion matters and it reduces the likelihood of technology adoption when farmers face uncertainty in groups of three. Neither risk aversion nor ambiguity aversion matter when farmers face uncertainty in groups of six. The third paper presents an impact assessment of integrated pest management on sweet gourd in Bangladesh. It employs an instrumental variable and marginal treatment effects approach to estimate the impact of IPM on yield and cost of sweet gourd in Bangladesh. The estimation methods consider both homogeneous and heterogeneous treatment effects. The paper finds that IPM adoption has a 7% - 34% yield advantage over traditional pest management practices. Results regarding the effect of IPM adoption on cost are mixed. IPM adoption alters production costs from -1.2% cost to +42%, depending on the estimation method employed. However, most of the cost changes are not statistically significant. Therefore, while we confidently argue that the IPM adoption provides a yield advantage over non-adoption, we do not find a robust effect regarding a cost advantage of adoption. / Ph. D.

The objectives of this dissertation were to evaluate genetic and environmental relationships between lamb and ewe traits including body weight, fleece weight and quality, prolificacy, body condition, ewe stayability and lamb survival. Average heritability estimates for lamb birth weight (BWT), weaning weight (WW), maternal weaning weight, yearling body weight, fleece weight, spinning count and staple length were 0.19, 0.09, 0.08, 0.35, 0.38, 0.25, and 0.31 respectively. Heritability estimates for adult traits averaged 0.43 for body weight (AW), 0.13 for body condition (AC), and 0.12 for number of lambs born per ewe lambing (NLB). Correlations between direct additive AW and direct additive and maternal lamb weights ranged from 0.21 to 0.96 (P < 0.05) and 0.29 to 0.53 (P < 0.05), respectively, with residual correlations ranging from 0.05 to 0.95. Correlations of lamb traits with adult body condition and NLB were generally not different from zero; genetic and residual correlations ranged from -0.52 to 0.69 and -.39 to 0.31, respectively. Ewe stayability was analyzed as overall stayability (STAYn|2) which indicated the presence or absence of a ewe at n yrs of age, given that she was present at 2 yrs of age, and marginal stayability (STAYn|1-n) recording the presences of a ewe at n yrs of age, given that she was in the flock the previous year. Additive variance in ewe stayability was only found in stayability at 5 and 6 yr of age (P < 0.05). Heritability estimates for STAY5|4 and STAY6|2 from multiple trait analyses with other traits averaged 0.08 and 0.10, respectively. Phenotypic correlations between STAY and all other traits were near zero, ranging from -0.04 to 0.03. The estimated correlations between additive effects on STAY5|4 and STAY6|2 and additive maternal effects on WW were positive (both 0.46; P < 0.05). Genetic correlations between STAY5|4 and WW, adult weight, and NLB were 0.06, 0.13 and -0.06 (P > 0.10), respectively. However, genetic correlations between STAY6|2 and WW, adult weight, and NLB were negative (-0.17, -0.32 (P < 0.05) and -0.03, respectively). Significant genetic variation was thus present in stayability, with nonzero genetic correlations present between STAY, maternal milk, WW, and adult weight. Survival analysis was performed using a proportional hazards model to measure the probability of lamb death before weaning. Lamb survival was recorded as the day of age at death. Records were censored if a live lamb was artificially removed from their litter before death. Fixed effects on survival included ewe age, litter size, sex, and linear and quadratic BWT. Average age of death was 13.7 d. Censoring of records before weaning occurred in 12.9% of the total lambs born. Risk ratios indicated lambs from yearlings and ewes older than 5 yr had the greater risk of death, as did triplet and quadruplet lambs. Linear and quadratic BWT effects on lamb survival were found (P < 0.05) and accounted for most of the litter size effects in large litters. The influence of informative censoring was considered by assuming that lambs censored by 3 d of age had died at the time of censoring. Heritability of lamb survival at 3 d of age (estimated using an animal model in MTDFREML) was near zero, ranging from 0.00 to 0.01. The lack of additive variance suggests that improvement in lamb survival should be made through changes in management practices. / Ph. D.

Thesis (M.Sc. (Statistics)) -- University of Limpopo, 2019 / Recurrent peritonitis is a major problem of peritoneal dialysis (PD) due to its association with technique failure in the dialysis process. The literature on peritonitis focused only on investigating major risk factors associated with the first episode of peritonitis. However, this dissertation investigates factors associated to multiple episodes of peritonitis, to a maximum of 6 episodes. The correlation of recurrent episodes of a patient is considered. The univariate counting process, stratified, gap-time and marginal hazard regression models are applied to select the significant covariates to the multivariate regression hazard models. Regression coefficient for covariates are found to be statistically significant at 5% level. The application of Akaike information criterion (AIC) and Schwarz bayesian criterion (SBC) assisted to filter out the best method which is the stratified regression hazard model. The major risk factors associated with recurrent episodes of peritonitis are examined from the selected good fitting model. In conclusion, the selected model identified two independent risk factors to be significantly associated with recurrent episodes of peritonitis: marital status and glomerularfiltrationrate. Twocategoriesofmaritalstatus, divorceandwidowerare the significant factors compared to married patients (when taking married patients as the reference category). / VLIROUC Programme