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DI, MARIA Chiara. "Longitudinal mediation analysis with structural and multilevel models: associational and causal perspectives." Doctoral thesis, Università degli Studi di Palermo, 2022. http://hdl.handle.net/10447/533485.
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LIU, XIAOQIU. "Managing Cardiovascular Risk in Hypertension: Methodological Issues in Blood Pressure Data Analysis." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/154475.
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Hypertension remains in 2017 a leading cause of mortality and disability worldwide. A number of issues related to the determinants of cardiovascular risk in hypertensive patients and to the strategies for better hypertension control are still pending. In such a context, aims of my research program were:
1. To investigate the contribution of blood pressure variability to the risk of cardiovascular mortality in hypertensive patients. In this setting, different methods for assessing blood pressure variability and different models exploring the link between blood pressure variability and outcome were investigated.
2. To assess the possibility that a hypertension management strategy based on hemodynamic assessment of patients through impedance cardiography might lead to a better hypertension control over 24 hours than a conventional approach only based on blood pressure measurement during clinic visits.
To these aims, this thesis summarizes data obtained by performing a). An in-depth analysis of a study conducted in the Dublin hypertensive population, including 11492 subjects, and b). The analysis of longitudinal data collected in the frame of BEAUTY (BEtter control of blood pressure in hypertensive pAtients monitored Using the hoTman® sYstem) study.
In Dublin study, the proportional hazard Cox model and accelerated failure time models have been used to estimate the additional effect of blood pressure variability on cardiovascular mortality over and above the effect of increased mean BP levels, with an attempt to identify the best threshold values for risk stratification.
On the other hand, in BEAUTY study, mixed model and generalized estimation equation are used for the longitudinal data analysis.
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COVA, ILARIA. "NUTRITIONAL STATUS AND BODY COMPOSITION BY BIOELECTRICAL IMPEDANCE VECTOR ANALYSIS: A CROSS-SECTIONAL AND LONGITUDINAL STUDY IN MILD COGNITIVE IMPAIRMENT AND ALZHEIMER¿S DEMENTIA." Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/545028.
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Aim To analyze nutritional status and body composition in Alzheimer’s disease (AD) and Mild Cognitive Impairment (MCI) with respect to elderly healthy controls (HC), in order to find any biomarker of disease.
Methods A cross-sectional and a longitudinal study was performed in a memory clinic of a University-Hospital, by recruiting patients with mild-moderate AD, subjects with MCI and HC. Nutritional status was assessed at baseline for all the subjects and repeated at follow-up in AD patients by anthropometric parameters (body mass index; calf, upper arm and waist circumferences), Mini Nutritional Assessment (MNA) and body composition by bioelectrical impedance vector analysis (BIVA). For the cross-sectional study variables were analyzed by analysis of variance and subjects were grouped by cognitive status and gender; for the cross-sectional study in AD variables were analyzed by dependent t-test for repeated measures and linear regression analysis within gender. MCI were follow-up by repetition of neuropsychological tests to detect a potential progression to dementia and AD. MCI subjects’ characteristics at baseline were compared by outcome using non-parametric statistics.
Results Sociodemographic variables did not differ among the three groups (59 mild AD, 34 MCI and 58 HC), except for females’ age, which was therefore used as covariate in a general linear multivariate model. MNA score was significantly lower in AD patients than in HC; MCI subjects achieved intermediate scores. AD patients (both sexes) had significantly (p<0.05) higher height-normalized impedance values and lower phase angles (body cell mass) compared with HC; a higher ratio of impedance to height was found in men with MCI with respect to HC. With BIVA method, MCI subjects showed a significant displacement on the RXc graph on the right side indicating lower soft tissues (Hotelling’s T2 test: men=10.6; women=7.9;p < 0,05) just like AD patients (Hotelling’s T2 test: men=18.2; women=16.9; p<0,001).
After 8.7 ± 3.6 months of follow-up, bioelectrical variables of 40 AD patients did not significantly change. Forty-three MCI (28 females, 15 males) were followed up for 14.4 ± 8.6 months; 8 (6 females, 2 males) of them progressed to AD. Due to the limited number of males progressed, only females MCI’s bioelectrical characteristics were analyzed and those who progressed to clinically evident AD showed lower phase angles than stable MCI with considerable trend toward significance (5.9 1.0 vs. 5.2 0.6, p 0.069).
Conclusion Bioelectrical parameters significantly differ from MCI and AD to HC, but remain stable after approximately 9 months of AD patients’ follow-up; MCI who progressed to clinically evident AD had a lower PA which approached the borderline of significance. Analysis of body composition with BIVA could detect early changes in body composition which may perhaps reflect early systemic manifestation of the AD process at MCI stage of disease, before anthropometric change becomes evident. Increasing the cohort of MCI and their longitudinal observation will provide further information to understand if a BIVA pattern indicating a worse nutritional status could be an early and sensitive marker of progression to dementia or specifically to AD in MCI subjects.
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BOLAZZI, FLORIANE. "CASTE, CLASS AND SOCIAL MOBILITY. A CASE STUDY IN NORTH INDIA 1958-2015." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/732484.
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This thesis analyses the nexus between caste, class and social mobility in rural India over the last half-century of profound transformations. The increase of demographic pressure on land has reduced agriculture to a subsidiary source of livelihood for the rural population. The transition from farming to informal and irregular forms of labour which require the working population to commute to small and medium towns, have become the predominant patterns of occupational transition in rural India.
This thesis investigates the nature and magnitude of these changes and their implications for the reconfiguration of the social structures - caste hierarchy and class stratification - and aims at verifying whether the caste membership continues to prevail as a factor of social stratification. Using unique data at the individual level on the full population of Palanpur, a village in Uttar Pradesh, surveyed seven times from 1958 to 2015, we provide a longitudinal analysis of the trends, the patterns and the determinants of the social mobility of three generations of individuals. We combine the statistical and econometric analysis of the social mobility with a qualitative analysis of more than a hundred interviews carried out during six-months in-depth fieldwork. We find evidence of the opportunities for social mobility to increase but prevalently downward toward manual workers’ class. The advantage of the upper castes to access high salariat positions persists over time, however, with the modernization, the educational attainment plays an equalising role on the chances of upward mobility irrespective of the caste and the class of origin. Moreover, we find that the caste disadvantage for upward mobility from low to middle and top-class decreased over time for some of the castes at the bottom of the hierarchy. While much social stratification research has been and still is carried out in Western countries, this thesis is an original contribution to the emerging literature concerning social stratification and mobility in developing countries.
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Petzold, Max. "Evaluation of information in longitudinal data." Göteborg : Statistical Research Unit, Göteborg University, 2003. http://catalog.hathitrust.org/api/volumes/oclc/52551306.html.
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Zhu, Liang. "Semiparametric analysis of multivariate longitudinal data." Diss., Columbia, Mo. : University of Missouri-Columbia, 2008. http://hdl.handle.net/10355/6044.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2008.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 3, 2009) Vita. Includes bibliographical references.
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Gashi, Arben, and Florent Sinani. "Adolescents, Sleep Deprivation and Externalizing Behaviour - Is There a Connection?" Thesis, Örebro universitet, Institutionen för juridik, psykologi och socialt arbete, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-65584.
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Rohé, Marc-Michel. "Représentation réduite de la segmentation et du suivi des images cardiaques pour l’analyse longitudinale de groupe." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4051/document.
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Cette thèse présente des méthodes d’imagerie pour l’analyse du mouvement cardiaque afin de permettre des statistiques groupées, un diagnostic automatique et une étude longitudinale. Ceci est réalisé en combinant des méthodes d’apprentissage et de modélisation statistique. En premier lieu, une méthode automatique de segmentation du myocarde est définie. Pour ce faire, nous développons une méthode de recalage très rapide basée sur des réseaux neuronaux convolutifs qui sont entrainés à apprendre le recalage cardiaque inter-sujet. Ensuite, nous intégrons cette méthode de recalage dans une pipeline de segmentation multi-atlas. Ensuite, nous améliorons des méthodes de suivi du mouvement cardiaque afin de définir des représentations à faible dimension. Deux méthodes différentes sont développées, l’une s’appuyant sur des sous-espaces barycentriques construits sur des frames de référence de la séquence et une autre basée sur une représentation d’ordre réduit du mouvement avec des transformations polyaffine. Enfin, nous appliquons la représentation précédemment définie au problème du diagnostic et de l’analyse longitudinale. Nous montrons que ces représentations en- codent des caractéristiques pertinentes permettant le diagnostic des patients atteint d’infarct et de Tétralogie de Fallot ainsi que l’analyse de l’évolution dans le temps du mouvement cardiaque des patients atteints de cardiomyopathies ou d’obésité. Ces trois axes forment un cadre pour l’étude du mouvement cardiaque de bout en bout de l’acquisition des images médicales jusqu’à leur analyse automatique afin d’améliorer la prise de décision clinique grâce à un traitement personnalisé assisté par ordinateurThis thesis presents image-based methods for the analysis of cardiac motion to enable group-wise statistics, automatic diagnosis and longitudinal study. This is achieved by combining advanced medical image processing with machine learning methods and statistical modelling. The first axis of this work is to define an automatic method for the segmentation of the myocardium. We develop a very-fast registration method based on convolutional neural networks that is trained to learn inter-subject heart registration. Then, we embed this registration method into a multi-atlas segmentation pipeline. The second axis of this work is focused on the improvement of cardiac motion tracking methods in order to define relevant low-dimensional representations. Two different methods are developed, one relying on Barycentric Subspaces built on ref- erences frames of the sequence, and another based on a reduced order representation of the motion from polyaffine transformations. Finally, in the last axis, we apply the previously defined representation to the problem of diagnosis and longitudinal analysis. We show that these representations encode relevant features allowing the diagnosis of infarcted patients and Tetralogy of Fallot versus controls and the analysis of the evolution through time of the cardiac motion of patients with either cardiomyopathies or obesity. These three axes form an end to end framework for the study of cardiac motion starting from the acquisition of the medical images to their automatic analysis. Such a framework could be used for diagonis and therapy planning in order to improve the clinical decision making with a more personalised computer-aided medicine
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Husain, Syeda Tasmine. "Bayesian analysis of longitudinal models /." Internet access available to MUN users only, 2003. http://collections.mun.ca/u?/theses,163598.
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Ryu, Duchwan. "Regression analysis with longitudinal measurements." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2398.
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Bayesian approaches to the regression analysis for longitudinal measurements are
considered. The history of measurements from a subject may convey characteristics
of the subject. Hence, in a regression analysis with longitudinal measurements, the
characteristics of each subject can be served as covariates, in addition to possible other
covariates. Also, the longitudinal measurements may lead to complicated covariance
structures within each subject and they should be modeled properly.
When covariates are some unobservable characteristics of each subject, Bayesian
parametric and nonparametric regressions have been considered. Although covariates
are not observable directly, by virtue of longitudinal measurements, the covariates
can be estimated. In this case, the measurement error problem is inevitable. Hence,
a classical measurement error model is established. In the Bayesian framework, the
regression function as well as all the unobservable covariates and nuisance parameters
are estimated. As multiple covariates are involved, a generalized additive model is
adopted, and the Bayesian backfitting algorithm is utilized for each component of the
additive model. For the binary response, the logistic regression has been proposed,
where the link function is estimated by the Bayesian parametric and nonparametric
regressions. For the link function, introduction of latent variables make the computing
fast.
In the next part, each subject is assumed to be observed not at the prespecifiedtime-points. Furthermore, the time of next measurement from a subject is supposed to
be dependent on the previous measurement history of the subject. For this outcome-
dependent follow-up times, various modeling options and the associated analyses
have been examined to investigate how outcome-dependent follow-up times affect
the estimation, within the frameworks of Bayesian parametric and nonparametric
regressions. Correlation structures of outcomes are based on different correlation
coefficients for different subjects. First, by assuming a Poisson process for the follow-
up times, regression models have been constructed. To interpret the subject-specific
random effects, more flexible models are considered by introducing a latent variable
for the subject-specific random effect and a survival distribution for the follow-up
times. The performance of each model has been evaluated by utilizing Bayesian
model assessments.
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Mills, Joanna E. "The analysis longitudinal binary data." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ57350.pdf.
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Fullwood, Catherine Lee. "Longitudinal analysis of anticoagulent data." Thesis, Lancaster University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431469.
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Bai, Yang, and 柏楊. "Statistical analysis for longitudinal data." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841756.
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Dufour, Alyssa Beth. "Cluster analysis of longitudinal trajectories." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12751.
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Thesis (Ph.D.)--Boston UniversityCluster analysis is widely used in many disciplines including biology, psychology, archaeology, geography, and marketing. Methods have been developed to extend cluster analysis to longitudinal data, clustering subject trajectories rather than single time points. Here, I examine 2 methods of longitudinal cluster analysis: k-means and model-based (implemented using FlexMix in R) cluster analysis. I compare these two methods based on the Correct Classification Rate, the ability of the method to correctly classify subject trajectories into groups, using a simulation study. Both methods are found to perform well under most circumstances, but in 64% of the scenarios examined, the model-based method out-performs the k-means approach. Next, I examine three criteria that have been used to determine how many groups exist in the data: the Akaike's Information Criteria (AIC), the Davies-Bouldin Index (DB), and the Calinski-Harabasz pseudo F-statistic (CH). The latter two were developed specifically for choosing the number of groups in a cluster analysis with a single observation per person, while the AIC was developed as a general model fit statistic. Few studies have used these criteria in the context of longitudinal data and no study has compared their efficacy. We found that the DB and CH fail to correctly identify the number of groups in the majority cases, while the AIC was better able to determine the correct number. Finally, as no study has examined the addition of a covariate to cluster analysis, we compare results of a cluster analysis when a covariate was taken into account to when it is ignored. When a covariate is both time-dependent and associated with the outcome, regardless of the magnitude of the association, it is important to take this variable into account in the analysis. If the covariate is associated only with the outcome and not time-dependent, depending on the magnitude of the association, it may be necessary to account for the covariate. In summary, we present methods for clustering trajectories, evaluate methods for determining the number of groups and determine the importance of adjusting for covariates in the cluster analysis of longitudinal data.
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Bai, Yang. "Statistical analysis for longitudinal data." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42841756.
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Kim, Yangjin. "Statistical analysis of longitudinal data /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p3100054.
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Cheung, Ka-yan, and 張嘉茵. "Multilevel modeling for the analysis of longitudinal periodontal data." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46605496.
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Rocha, Everton Batista da. "Modelos para a análise de dados de contagens longitudinais com superdispersão: estimação INLA." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/11/11134/tde-05112015-144057/.
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Em ensaios clínicos é muito comum a ocorrência de dados longitudinais discretos. Para sua análise é necessário levar em consideração que dados observados na mesma unidade experimental ao longo do tempo possam ser correlacionados. Além dessa correlação inerente aos dados é comum ocorrer o fenômeno de superdispersão (ou sobredispersão), em que, existe uma variabilidade nos dados além daquela captada pelo modelo. Um caso que pode acarretar a superdispersão é o excesso de zeros, podendo também a superdispersão ocorrer em valores não nulos, ou ainda, em ambos os casos. Molenberghs, Verbeke e Demétrio (2007) propuseram uma classe de modelos para acomodar simultaneamente a superdispersão e a correlação em dados de contagens: modelo Poisson, modelo Poisson-gama, modelo Poisson-normal e modelo Poisson-normal-gama (ou modelo combinado). Rizzato (2011) apresentou a abordagem bayesiana para o ajuste desses modelos por meio do Método de Monte Carlo com Cadeias de Markov (MCMC). Este trabalho, para modelar a incerteza relativa aos parâmetros desses modelos, considerou a abordagem bayesiana por meio de um método determinístico para a solução de integrais, INLA (do inglês, Integrated Nested Laplace Approximations). Além dessa classe de modelos, como objetivo, foram propostos outros quatros modelos que também consideram a correlação entre medidas longitudinais e a ocorrência de superdispersão, além da ocorrência de zeros estruturais e não estruturais (amostrais): modelo Poisson inacionado de zeros (ZIP), modelo binomial negativo inacionado de zeros (ZINB), modelo Poisson inacionado de zeros - normal (ZIP-normal) e modelo binomial negativo inacionado de zeros - normal (ZINB-normal). Para ilustrar a metodologia desenvolvida, um conjunto de dados reais referentes à contagens de ataques epilépticos sofridos por pacientes portadores de epilepsia submetidos a dois tratamentos (um placebo e uma nova droga) ao longo de 27 semanas foi considerado. A seleção de modelos foi realizada utilizando-se medidas preditivas baseadas em validação cruzada. Sob essas medidas, o modelo selecionado foi o modelo ZIP-normal, sob o modelo corrente na literatura, modelo combinado. As rotinas computacionais foram implementadas no programa R e são parte deste trabalho.Discrete and longitudinal structures naturally arise in clinical trial data. Such data are usually correlated, particularly when the observations are made within the same experimental unit over time and, thus, statistical analyses must take this situation into account. Besides this typical correlation, overdispersion is another common phenomenon in discrete data, defined as a greater observed variability than that nominated by the statistical model. The causes of overdispersion are usually related to an excess of observed zeros (zero-ination), or an excess of observed positive specific values or even both. Molenberghs, Verbeke e Demétrio (2007) have developed a class of models that encompasses both overdispersion and correlation in count data: Poisson, Poisson-gama, Poisson-normal, Poissonnormal- gama (combined model) models. A Bayesian approach was presented by Rizzato (2011) to fit these models using the Markov Chain Monte Carlo method (MCMC). In this work, a Bayesian framework was adopted as well and, in order to consider the uncertainty related to the model parameters, the Integrated Nested Laplace Approximations (INLA) method was used. Along with the models considered in Rizzato (2011), another four new models were proposed including longitudinal correlation, overdispersion and zero-ination by structural and random zeros, namely: zero-inated Poisson (ZIP), zero-inated negative binomial (ZINB), zero-inated Poisson-normal (ZIP-normal) and the zero-inated negative binomial-normal (ZINB-normal) models. In order to illustrate the developed methodology, the models were fit to a real dataset, in which the response variable was taken to be the number of epileptic events per week in each individual. These individuals were split into two groups, one taking placebo and the other taking an experimental drug, and they observed up to 27 weeks. The model selection criteria were given by different predictive measures based on cross validation. In this setting, the ZIP-normal model was selected instead the usual model in the literature (combined model). The computational routines were implemented in R language and constitute a part of this work.
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Boudreau, Christian. "Duration data analysis in longitudinal surveys." Waterloo, Ont. : University of Waterloo, 2003. http://etd.uwaterloo.ca/etd/cboudrea2003.pdf.
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Thesis (Ph.D.)--University of Waterloo, 2003."A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor of Philosophy in Statistics". Includes bibliographical references. Also available in microfiche format.
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Boudreau, Christian. "Duration Data Analysis in Longitudinal Survey." Thesis, University of Waterloo, 2003. http://hdl.handle.net/10012/1043.
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Considerable amounts of event history data are collected through longitudinal surveys. These surveys have many particularities or features that are the results of the dynamic nature of the population under study and of the fact that data collected through longitudinal surveys involve the use of complex survey designs, with clustering and stratification. These particularities include: attrition, seam-effect, censoring, left-truncation and complications in the variance estimation due to the use of complex survey designs. This thesis focuses on the last two points.
Statistical methods based on the stratified Cox proportional hazards model that account for intra-cluster dependence, when the sampling design is uninformative, are proposed. This is achieved using the theory of estimating equations in conjunction with empirical process theory. Issues concerning analytic inference from survey data and the use of weighted versus unweighted procedures are also discussed. The proposed methodology is applied to data from the U. S. Survey of Income and Program Participation (SIPP) and data from the Canadian Survey of Labour and Income Dynamics (SLID).
Finally, different statistical methods for handling left-truncated sojourns are explored and compared. These include the conditional partial likelihood and other methods, based on the Exponential or the Weibull distributions.
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Ricci, Peter J. "Some aspects of longitudinal data analysis /." Title page, contents and summary only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phr491.pdf.
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Fear, Simon Charles. "The analysis of categorical longitudinal data." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266052.
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Sen, Sharma Pradeep Kumar. "Sensitivity analysis of ship longitudinal strength." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/45183.
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The present work addresses the usefulness of a simple and efficient computer program (ULTSTR) for a sensitivity analysis of ship longitudinal strength, where this program was originally developed for calculating the collapse moment. Since the program is efficient it can be used to obtain ultimate strength variability for various values of parameters which affects the longitudinal strength, viz., yield. stress, Young's modulus, thickness, initial imperfections, breadth, depth, etc.
The results obtained with this approach are in good agreement with those obtained by use of a more complex nonlinear finite element program USAS, developed by American Bureau of Shipping.Master of Science
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Stern, Theresa Marie Papa. "Longitudinal analysis of incomplete binary data /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487947501135652.
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Gao, Dexiang. "Analysis of clustered longitudinal count data /." Connect to full text via ProQuest. Limited to UCD Anschutz Medical Campus, 2007.
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Thesis (Ph.D. in Analytic Health Sciences, Department of Preventive Medicine and Biometrics) -- University of Colorado Denver, 2007.Typescript. Includes bibliographical references (leaves 75-77). Free to UCD affiliates. Online version available via ProQuest Digital Dissertations;
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Schabenberger, Oliver. "The analysis of longitudinal ordinal data." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-02272007-092413/.
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Yao, Fang. "Functional data analysis for longitudinal data /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Mace, Tiphaine. "Physiologie et génétique de la dynamique des réserves corporelles des ovins allaitants dans un milieu contraignant." Thesis, Toulouse, INPT, 2020. http://www.theses.fr/2020INPT0069.
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Depuis quelques années, l’élevage doit répondre à de nouvelles contraintes liées au changement climatique et adopter des principes proposés par l’agroécologie pour assurer sa durabilité. L’utilisation d’animaux plus robustes peut permettre de répondre à ces nouveaux défis. Une des composantes de cette robustesse est la dynamique des réserves corporelles (DRC ; alternance de périodes de mobilisation (MO) et de reconstitution (RE) des RC). Ce mécanisme biologique permet aux ruminants de faire face aux périodes avec un bilan énergétique négatif (BEN). L’objectif de ma thèse est d’approfondir les connaissances sur ce sujet en caractérisant la DRC au cours de plusieurs cycles de production et en étudiant le déterminisme génétique de cette dynamique chez les ovins allaitants. Les données utilisées proviennent de suivis longitudinaux d’état corporel et de poids vif de brebis allaitantes Romane, élevées en plein air intégral à La Fage (Causses du Larzac). La caractérisation de la DRC indique qu’il existe plusieurs grands types de trajectoires de variation d’état corporel au cours des stades physiologiques des brebis. Les différences de niveau et de forme de ces trajectoires s’expliquent principalement par de la variabilité interindividuelle. La modélisation mathématique de la DRC a permis de définir des critères synthétiques des capacités de MO et RE des RC. Par ailleurs, de faibles corrélations, mais favorables, entre la DRC et d’autres performances de production indiquent que plus la brebis mobilise ses RC durant les périodes de BEN, meilleures sont les performances de production. L’étude du déterminisme génétique de la DRC a permis de mettre en évidence qu’il s’agit d’un caractère héritable et que les mécanismes de MO et RE des RC sont fortement liés génétiquement. Le nombre élevé et les faibles effets des zones du génome associées à la DRC suggèrent un déterminisme polygénique. Enfin, de nombreux gènes candidats ont été identifiés dans ces régions génomiques déjà décrits pour leurs liens avec des caractères d’adiposité, de croissance et les métabolismes énergétique. Ainsi, l’utilisation de la DRC en sélection génétique peut être envisagée chez les ruminants, même si des travaux complémentaires doivent être poursuivis notamment par l’étude des interactions génotype x milieu sur ce caractèreDuring the last few years, livestock keepers had to respond to new constrains linked to the climate change and to adopt principles proposed by agroecology to ensure their sustainability. The use of more robust animals can allow responding to these new challenges. One component of this robustness is the body reserves’ dynamic (BRD; i.e. alternation of BR mobilization (MO) and accretion (AC) periods). Such mechanism allows the ruminants to cope with negative energy balances (NEB). My thesis objective is to get new insights in such a complex subject, through an effort looking to deep BRD characterization during several production cycles while investigating the related genetic determinism of this trait in meat ewes. The data used come from longitudinal measurements of body weight and body condition score of Romane meat ewes reared under the extensive rangeland conditions of La Fage (Causses du Larzac). Characterization of BRD showed the existence of several trajectories describing body condition changes throughout ewe’s physiological stages. Differences in the level and shape of trajectories were mainly due to interindividual variability. Modelling of BRD produced few synthetic criteria for estimation of individual capacity of BR MO and AC. In addition, low but favorable correlations between BRD traits and ewes production performances indicated that more ewes will mobilize their BR, better their production performance will be. The genetic determinism study demonstrated that BRD traits are heritable and BR MO and AC processes are genetically linked. High number and small effects of QTLs associated to BRD traits suggest a polygenic determinism. Finally, several candidate genes were identified in the QTL regions, which have been previously described to be related to fat traits, growth traits or energy metabolism. The use of BRD in genetic selection may be considered in ruminants, even if complementary works must be performed, particularly with the genotype x environment study on this trait
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Jiang, Xiaoping. "Nonparametric quasi-likelihood in longitudinal data analysis." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2078.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Mathematical Statistics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Li, Zuojing. "Longitudinal data analysis using generalized linear models." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27267.
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In this work we examine various conditions under which the usual asymptotic results (i.e. the weak consistency, the asymptotic normality and the strong consistency) hold for the regressor parameter beta which arises in a linear model (Chapter 2), a generalized linea model (GLM) with a fully specified likelihood (Chapter 3) or as a root of the generalized estimating equation (GEE) associated with a sequence of longitudinal observations (Chapter 4). Our main references for each of these chapters are [12], [9], respectively [20].
We provide detailed proofs of the results found in the above-mentioned references, and we extend the results of [9] to, the case of stochastic regressors (Section 3.4). Finally, in Chapter 5, we identify a fundamental mistake appearing in the recent article [4], which examines the strong consistency of the regressor parameter beta in a GLM for which the likelihood of the density is not specified. In Section 5.2, we give a correction to the main theorem of [4], as well as some new results concerning the weak consistency and asymptotic normality of beta.
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Sewart, Pete. "Graphical and longitudinal models in credit analysis." Thesis, Lancaster University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387438.
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Price, Julia, Kelly Price, and Jamie H. Price. "Online Doctoral Student Perceptions: A Longitudinal Analysis." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etsu-works/6031.
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Presenters will demonstrate concrete examples and supporting research regarding professor presence within online courses. Additionally, the presentation will address the skill of transforming this content into practice, valuable practical applications, the importance of professor presence in the online classroom, and why such presence is important in building a learning community in the online environment. The presentation is appropriate for all instructors of blended and exclusively online environments.
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Green, Brittany. "Ultra-high Dimensional Semiparametric Longitudinal Data Analysis." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1593171378846243.
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Zhao, Rui. "Integrated Analysis of Longitudinal Tumor Burden Data." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14226076.
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The first part of this thesis introduces a new statistical method to estimate parameter values in a mixed population consisting of both single- and bi- phasic longitudinal trajectories. This pro- posed model is capable of categorizing patients according to their longitudinal relationships and estimating the associated parameters of interest, while accounting for between-patient variability. We applied this method to a large phase III randomized trial and found significant differences in patients between different treatment cohorts and within the same treatment cohort, in terms of their longitudinal relationships, with the majority of patients displaying complex bi-phasic trends. In the second part of this thesis, we designed a dynamical system model to explain the observed bi-phasic longitudinal trends and their implications for the underlying cancer biology. We found that a hybrid model encompassing both hierarchical cellular model and clonal expansion model is needed to explain the observed bi-phasic patterns. The third part of this thesis explores the effects of proliferative patterns in colon crypt on crypt stability and rates of somatic evolution.
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Moore, Page Casey Seaman John Weldon. "A restriction method for the analysis of discrete longitudinal missing data." Waco, Tex. : Baylor University, 2006. http://hdl.handle.net/2104/4880.
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DA, RE FULVIO. "An MRI-based analysis of the longitudinal progression of atrophy in amnestic and non-amnestic phenotypes of Alzheimer’s disease." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/261941.
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Recenti studi sulla progressione della malattia d’Alzheimer(AD)suggeriscono che la patologia possa essere trasmessa da un’area all’altra del cervello tramite diffusione locale o lungo le fibre assonali.Tuttavia,quest’ipotesi necessita di maggiori conferme ed è ancora meno chiaro se questi modelli possano essere applicabili alle varianti non amnesiche di AD(naAD),un gruppo di fenotipi AD caratterizzati da relativo risparmio all’esordio della memoria episodica e deficit cognitivi dominio-specifici.Pochi studi ad oggi hanno infatti analizzato la progressione longitudinale della malattia in naAD, tutti al massimo con due sole di queste varianti.
Inizialmente abbiamo confrontato 240 RMN pesate in T1 da 129 pazienti AD con RMN di controlli sani per stabilire l’atrofia in 120 regioni di interesse(ROI); poi abbiamo calcolato modelli di progressione di malattia separatamente per ogni fenotipo: AD amnesici(aAD),variante logopenica di afasia primaria progressiva(lvPPA),atrofia corticale posteriore(PCA)e variante frontale di AD(fvAD).Tutti i pazienti avevano evidenza di patologia AD tramite dati autoptici o da liquor cefalorachidiano(CSF).I risultati dalla coorte di aAD sono stati utilizzati per determinare i parametri per l’algoritmo di assegnazione delle fasi,basato sull’associazione con lo staging di patologia di Braak.
Per ogni variante AD,4 fasi di atrofia regionale sono state definite sulla base della frequenza decrescente di atrofia tra i soggetti.Abbiamo osservato pattern unici di atrofia cumulativa per ogni fenotipo.Le ROI di fase 1 nel nostro modello rappresentano l’origine anatomica di ogni fenotipo,inclusi: il lobo temporale mesiale(MTL)per il gruppo aAD(risparmiato negli altri gruppi),il lobo temporale sinistro nella lvPPA,la corteccia parieto-occipitale nella PCA,quella temporo-parietale per la CBS e le aree fronto-temporali per la fvAD.Successivamente abbiamo assegnato una fase ad ogni RMN dei pazienti in base alla somiglianza dei pattern di atrofia regionale con l’atrofia predetta per il fenotipo corrispondente ad ogni fase.Le fasi ROI erano correlate con parametri patologici disponibili,mentre le fasi RMN erano correlate con misure demografiche e cliniche.
Dopodiché abbiamo deciso di studiare le modifiche nel tempo della sostanza grigia(GM)in una coorte di pazienti in parte sovrapposta a quella usata per lo studio trasversale,ad esclusione di CBS: 17 aAD,25 lvPPA,20 PCA e 12 fvAD,con 37 controlli abbinati.Abbiamo analizzato il volume della GM e le sue modifiche longitudinali nelle ROI di fase 1 dallo studio trasversale per naAD e l’MTL per aAD.Abbiamo anche studiato l’atrofia longitudinale al di fuori di queste aree tramite un’analisi accessoria all’intero cervello e abbiamo comparato i fenotipi tra loro.
Abbiamo osservato pattern regionali unici di atrofia iniziale e diffusione longitudinale nella neocorteccia con tassi differenti in lvPPA,PCA e fvAD,che correlavano con i deficit cognitivi.La progressione di atrofia nel tempo ha coinvolto aree sia prossimali sia distanti dal sito d’esordio della malattia,suggerendo quindi più meccanismi di diffusione della patologia coinvolti; per quanto riguarda il secondo,in particolare,una misura di connettività strutturale prediceva la severità di atrofia longitudinale,corroborando quindi l’ipotesi delle vie lunghe.Nell’MTL,i pazienti naAD mostravano al basale meno atrofia dei pazienti aAD,ma i tassi longitudinali non erano diversi tra gruppi; il relativo risparmio dell’MTL in naAD potrebbe quindi essere dovuto a un esordio più tardivo della degenerazione nell’MTL rispetto all’aAD,considerando che l’età più avanzata era associata con atrofia in quest’area,indipendentemente dal gruppo.
Il presente studio ha corroborato probabili aree di malattia precoce in naAD e mostrato che ogni fenotipo ha un diverso pattern di progressione di atrofia lungo la corteccia,fornendo anche dati importanti sulla trasmissione della patologia.Recent studies of Alzheimer’s disease (AD) spread suggest that pathology may be transmitted from one brain area to another either via local diffusion or long-way transport via white matter pathways. However, this hypothesis requires more confirmations, and it’s even more unclear whether such models are applicable in non-amnestic AD (naAD), a group of AD phenotypes characterized by relative spared episodic memory at onset and domain-specific cognitive impairments. Few studies to date have in fact addressed the longitudinal spread of disease in naAD, and all of them considering no more than two variants. At first we compared 240 T1-weighted anatomical MRIs from 129 AD patients with elderly controls’ scans to assess atrophy in each of 120 regions-of-interest (ROIs); then we computed disease progression models separately for each phenotype: typical amnestic AD (aAD), logopenic variant primary progressive aphasia (lvPPA), posterior cortical atrophy (PCA), corticobasal syndrome (CBS), and frontal-variant AD (fvAD). All patients had autopsy or cerebrospinal fluid (CSF) evidence of AD pathology. Results from the amnestic cohort were used to determine appropriate parameters for the phase assignment algorithm, based on association with Braak pathology staging. For each AD variant, 4 phases of regional atrophy were defined based on decreasing frequency of atrophy across participants. We observed a unique distribution of accumulating atrophy for each phenotype. Phase 1 ROIs in our model represent the anatomical origin for each phenotype, including: medial temporal lobe (MTL) for the aAD group (spared in the other phenotypes), left lateral temporal lobe for lvPPA, occipito-parietal cortex for PCA, temporo-parietal cortex for CBS, and fronto-temporal cortex for fvAD. We subsequently assigned a phase to each patient MRI scan based on the similarity of regional atrophy patterns with atrophy predicted for the corresponding phenotype at each phase. ROI phases were strongly correlated with available pathological factors, while MRI phase was significantly correlated with demographic and clinical measures. Then we decided to investigate grey matter (GM) change over time in MRIs within a cohort of patients partly overlapping with the sample used for the cross-sectional study, with the exception of CBS patients (insufficient longitudinal data): 17 aAD, 25 lvPPA, 20 PCA, and 12 fvAD patients, compared to 37 matched controls. We analyzed GM volume and its longitudinal change in phase 1 ROIs from the cross-sectional study for naAD variants, and in MTL for aAD. We also investigated longitudinal atrophy outside these areas through an accessory whole-brain analysis, and we compared phenotypes between each other. We observed unique regional patterns of initial atrophy and longitudinal neocortical disease spread with different rates in lvPPA, PCA, and fvAD, which correlated with cognitive impairments. Atrophy spread over time included both proximal and distant regions from the hypothesized focus of disease onset, thus suggesting that multiple mechanisms of disease progression may have been involved; for what concerns the second mechanism, in particular, a measurement of structural connectivity predicted the severity of longitudinal atrophy, thus corroborating the hypothesis of long-distance fiber pathways. In MTL regions, naAD patients had less severe atrophy than aAD patients at baseline, but longitudinal rates did not differ between groups; MTL sparing in naAD may be due to later onset of MTL degeneration than in aAD, considering that older age was associated with atrophy in this area, independent of group. The current study corroborated probable areas of early disease for naAD and showed that each phenotype has a different pattern of atrophy progression across the cortex, providing also important data about pathology transmission.
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Zheng, Yingye. "Semiparametric methods for longitudinal diagnostic accuracy /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/9580.
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Tchatchueng, Mbougua Jules Brice. "Problématiques statistiques rencontrées dans l’étude du traitement antirétroviral des adultes infectés par le VIH en Afrique subsaharienne." Thesis, Montpellier 1, 2012. http://www.theses.fr/2012MON1T006/document.
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Partant de problématiques statistiques rencontrées dans l'étude du traitement antirétroviral des adultes infectés par le virus de l'immunodéficience humaine (VIH) en Afrique subsaharienne, cette thèse cherche, d'une part, à favoriser la vulgarisation d'outils méthodologiques relativement récents auprès d'un public d'utilisateurs moins avertis et, d'autre part, à participer au développement de nouveaux outils. Le premier chapitre présente différentes méthodes de modélisation des données longitudinales dont des méthodes d'analyse de l'évolution d'un critère au cours du temps (les modèles linéaires mixtes généralisés et les modèles d'équations d'estimation généralisées) ou de la survenue d'un évènement au cours du temps (le modèle semi-paramétrique de Cox et ses extensions à la prise en compte des covariables dépendantes du temps et de la censure informative). Le deuxième chapitre s'intéresse aux tests de non-infériorité et propose deux développements de la procédure classique de ces tests pour les cas où la marge de non-infériorité est relative. Enfin, le troisième chapitre aborde la question des données manquantes et propose une extension de la méthode d'imputation multiple par les distributions conditionnelles univariées qui consiste à prendre en compte des effets non-linéaires des covariables dans les modèles d'imputation par des fonctions B-splines. Ces méthodes sont illustrées par des études sur le VIH au Cameroun et au SénégalOn the basis of statistical challenges encountered in study of antiretroviral treatment of adults infected with human immunodeficiency virus (HIV) in sub-Saharan Africa, this thesis aims to promote the dissemination of relatively recent methodological tools of less aware audience of users on one hand and to participate to development of new tools on the other hand. The first chapter presents various methods for modeling longitudinal data of which analysis methods for changing of a criterion over time (the generalized linear mixed models and models of generalized estimating equations) or the occurrence of an event over time (the semi-parametric Cox model and its extensions to take into account time-dependent covariates and informative censoring). The second chapter focuses on non-inferiority test and provides two developments of the classical procedure of these tests in cases where the non-inferiority margin is relative. The third chapter addresses the question of missing data and proposes an extension of the multiple imputation method based on fully conditional specification, to take into account nonlinear effects of covariates in the imputation models using B-splines functions. These methods are illustrated by studies on HIV in Cameroon and Senegal
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Villeneuve, Claire. "Déterminants et évolution de profils de qualité de vie et d’adhésion aux traitements : analyse dans une cohorte de patients transplantés rénaux." Thesis, Limoges, 2016. http://www.theses.fr/2016LIMO0053/document.
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En parallèle des facteurs cliniques et biologiques, de nombreux déterminants psychologiques, dont l’adhésion et la qualité de vie, peuvent influencer la survie des greffons et des patients transplantés. Dans ce contexte notre objectif était d’étudier l’hétérogénéité des profils d’évolution de la qualité de vie et d’adhésion chez les patients transplantés rénaux et d’en identifier les déterminants. Dans un premier temps, l’étude de la qualité de vie a permis d’identifié deux sous-populations homogènes de patients: une majorité présentaient une qualité de vie semblable à la population générale alors que 40% des patients montraient une qualité de vie dégradée associé à une augmentation d’épisodes d’anxiété et de faiblesse musculaire. Nous avons pu montrer, dans un deuxième temps, qu’il existait deux profils d’évolution de l’adhésion : la majorité des patients étaient adhérents alors que 15 % des patients présentaient une non-adhésion en constante augmentation, une qualité de vie mentale dégradée et de plus nombreux épisodes de dépression. Enfin, nous présentons dans ce travail un nouvel outil dédié à l'évaluation de l’adhésion aux immunosuppresseurs des patients transplantés francophones. Cette thèse fournit de nouveaux outils, facile à utiliser précocement ou à distance de la greffe, permettant de détecter les patients présentant une qualité de vie et/ou une adhésion dégradée afin de mettre en place, pour ces patients, une prise en charge personnaliséeIn parallel to clinical and biological factors, many psychological determinants could influence transplant patient grafts survival and contributes to patients’ morbidity and mortality. Among them, adherence and quality of life were largely reported. In this context, our objective was to study, in kidney transplant patients, quality of life and adherence time-profiles heterogeneity and to identify determinants of distinct time-course. First, we identified two homogeneous subpopulations of patients: a majority presented a quality of life similar to the general population, while 40% of patients showed a poor quality of life associated with more episodes of anxiety and muscle weakness. Secondly, we found two distinct adherence time-profiles: the majority of patients were adherent while 15% presented a non-adherence constantly increasing associated with a poor mental quality of life and more depressive episodes. Finally, we proposed in this work a new tool dedicated to the evaluation of adherence in French-speaking transplant patients. This thesis provides new tools, easy to use even early on after transplantation, to detect patients with poor quality of life and / or adhesion in order to individualize the management of these patients with appropriate interventions
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Fatima, Kaniz. "Analysis of longitudinal data with ordered categorical response." Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239058.
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French, Benjamin. "Analysis of aggregate longitudinal data with time-dependent exposure /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/9569.
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Zins, Marie. "Déterminants sociaux des consommations d’alcool dans la cohorte gazel." Thesis, Paris 11, 2011. http://www.theses.fr/2011PA11T038/document.
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Les travaux présentés concernent essentiellement l’étude de certains déterminants sociaux des consommations d’alcool. Il s’agit d’analyser comment certains aspects des circonstances de vie, de travail et l’environnement social peuvent influencer ce comportement et modifier les consommations d’alcool au cours du temps.Ces analyses ont été menées dans la cohorte Gazel, composée de plus de 20 000 sujets(15 000 hommes et 5 000 femmes) employés d’EDF‐GDF et âgés de 35 à 50 ans à l’inclusion en 1989. Les déterminants étudiés sont les conditions de travail, le statut marital des femmes et les changements de statut au cours de la vie, ainsi que le passage à la retraite.Globalement, on observe que l’environnement professionnel, familial et social sont des déterminants de l’évolution des habitudes de consommation, et jouent un rôle souvent socialement différencié, les différentes catégories sociales ne se comportant habituellement pas de la même façon dans des situations comparablesThis thesis is about the social determinants of alcohol consumption. More specifically, the aims were to study how some circumstances of life, working and social environment may exert an influence on changes in drinking behaviours over time.The analyses were conducted within the Gazel cohort, including more than 20 000 subjects(15 000 men and 5 000 women) employees of EDF‐GDF, the French national utility company,aged 35‐50 at the inception of the cohort in 1989, which were followed‐up since that period.The main determinants that were studied are the working conditions, the marital status of women, and retirement. The main findings showed that the occupational, familial and social environment play a role in the changes in drinking behaviours over time, and that their effects are socially patterned
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Wagenhausen, Falk. "Tendances d'évolution en termes de mutualisation de la logistique urbaine : une comparaison France-Allemagne." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM2013.
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La population mondiale a dépassé les 7,3 milliards de personnes en 2011 et elle vit à plus de 50 % dans les villes. Ceci n’est pas sans générer de nombreux problèmes. Les espaces urbains, notamment en Europe, sont congestionnés par la faute d’une circulation croissante de personnes, de biens et de déchets, dont les impacts environnementaux sont significatifs. Les questions liées à la logistique urbaine donnent naturellement lieu à de plus en plus de recherches académiques. La thématique de la mutualisation de la logistique urbaine (MLU) connaît en particulier un grand succès depuis 2010, comme reflet d’expérimentations en cours, entre autres en Allemagne et en France. Sur la base d’une analyse approfondie de six revues professionnelles utilisées comme corpus de données secondaires, la recherche s’interroge sur l’évolution différenciée de la MLU en France et en Allemagne. Elle a pour objectif une meilleure compréhension d’un objet de recherche complexe qui reste finalement peu étudié. L’investigation, fondée sur une méthodologie post hoc et longitudinale, fait émerger un grand nombre d’éléments et met en lumière l’évolution comparée de la MLU dans les deux pays retenus. Les résultats sont synthétisés dans une grille de lecture compréhensive identifiant des cycles de MLU et relevant la diversité actuelle des solutions techniques et organisationnelles. Ces solutions débouchent sur de nouvelles réflexions concernant entre autres l’action des Pouvoirs publics, et sur des retours d’expérience quant aux enjeux des différents types d’espaces logistiques urbains à implémenterIn 2011, the world population exceeded 7.3 billion people, with more than 50% living in cities. This has not happened without generating many problems. Urban spaces, particularly in Europe, are already highly congested due to a growing of population, goods, and waste, all of which have a significant impact on the environment. Issues related to urban logistics naturally lead to more academic research, particularly in urban logistics mutualization (ULM), which has significantly increased since 2010 as a reflection of current experimentation, especially in Germany and France. Based on an in-depth analysis of six professional journals used as corpus of secondary data, the research question is to find out the differentiated development of the ULM in France and Germany. The objective of this doctoral thesis is to better understand the complex research subject, ULM, which is currently insufficiently studied. The investigation, based on a post hoc and longitudinal methodology, brings out a large number of items as well as highlights the comparative development of the ULM in these two selected countries. The results are summarized in a comprehensible reading grid identifying ULM cycles within the current diversity of technical and organizational solutions. These solutions lead to new ideas concerning the actions of public authorities, in turn providing feedback about the challenges of implementing urban logistics spaces
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Sucheston, Lara E. "STATISTICAL METHODS FOR THE GENETIC ANALYSIS OF DEVELOPMENTAL DISORDERS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1175883318.
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Abichou, Klich Amna. "Décomposition de la variance dans le modèle de classification de trajectoires de biomarqueurs." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1199/document.
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L’analyse de mesures longitudinales –appelées trajectoires– est de plus en plus fréquente en recherche médicale. L’un des intérêts de cette analyse est d’identifier des groupes d’individus ayant des trajectoires similaires. La classification obtenue peut être utilisée pour mieux comprendre l’hétérogénéité des évolutions entre individus. La classification peut être déterminée à partir d’un modèle pour lequel les trajectoires des individus correspondent à la trajectoire du groupe auquel ils sont affectés. L’objectif de la thèse est de développer une extension de ce modèle de classification standard permettant une meilleure prise en compte de la variabilité au sein des groupes, (i) variabilité des valeurs du marqueur (variance résiduelle) et (ii) variabilité des profils d’évolution (variance inter-individuelle). Deux modèles de classification sont développés : 1) un premier modèle qui prend en compte une variance résiduelle au sein de chaque groupe variable d’un groupe à l’autre, et 2) un deuxième modèle qui prend en compte une variabilité des trajectoires au sein des groupes au lieu de de prédire la même trajectoire pour tous les individus d’un même groupe, variabilité qui peut être identique ou variable d’un groupe à l’autre. L’intérêt de ces deux modèles a été montré par des travaux de simulations et par des applications cliniques. Globalement, lorsque le nombre de mesures et de trajectoires est suffisant, ces modèles donnent de meilleures classifications que celles du modèle de classification standard. Par ailleurs, en dehors de plans expérimentaux très contrôlés, les deux sources de variabilité sont inhérentes à la recherche en santé. Ces modèles sont donc très pertinents d’un point de vue cliniqueThe analysis of longitudinal measures –called trajectories– is more and more frequent in clinical research. One of the interests of this analysis is to identify groups of individuals with similar trajectories. The obtained classification is used to understand and explore the heterogeneity of trajectories among subjects. The classification can be performed by a model that predicts the same trajectory for all the subjects that are classified in the same group. The objective of this thesis is to develop an extension to the standard classification model that gives greater consideration to the variability within groups, (i) the variability of marker values (residual variance), and (ii) the variability of the individual trajectories inside a group (between-individual variance). Two classification models were developed: 1) a first model that allows unequal residual variance across groups, and 2) a second model that takes into account a between-individual variance within each group instead of predicting the same trajectory for all subjects in the same group, a variance that can be equal or unequal across groups. The interest of these two models has been studied by simulations and through clinical applications. Overall, when the number of trajectories and measurements per trajectory is sufficient, these models gives better classification compared to the standard classification model. Moreover, except for highly controlled experimental designs, the two sources of variability are inherent to research in health. Therefore, these models are very relevant from a clinical point of view
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Modur, Sharada P. "Missing Data Methods for Clustered Longitudinal Data." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1274876785.
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Barry, Sarah Jane Elizabeth. "Longitudinal analysis of three-dimensional facial shape data." Connect to e-thesis, 2008. http://theses.gla.ac.uk/190/.
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Thesis (Ph.D.) - University of Glasgow, 2008.Ph.D. thesis submitted to the Faculty of Information and Mathematical Sciences, Department of Statistics, University of Glasgow, 2008. Includes bibliographical references. Print version also available.
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Barry, Sarah J. E. "Longitudinal analysis of three-dimensional facial shape data." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/190/.
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Shape data encompass all the information that is left to describe a shape following removal of location, rotation and scale effects. Much work has been done in the analysis of two-dimensional shapes depicted by anatomical landmarks placed at points of importance. Less has been carried out in the area of three-dimensional shapes, particularly in terms of growth or change over time. This thesis considers the analysis of such longitudinal three-dimensional shape data. In doing so, two well established but normally unrelated areas of Statistics are brought together: those of longitudinal data analysis (specifically, linear mixed effects models) and shape analysis. A recently proposed method of analysing longitudinal high-dimensional data is presented in a novel application within the area of shape analysis, illustrated by a study comparing the facial shapes of cleft-lip and palate children with controls as they grow from three months to two years of age. Both anatomical landmarks and facial curves are considered. Chapter 1 broadly introduces the areas of shape analysis, linear mixed effects models and dimension reduction. Standard methods for measuring shapes are introduced, along with the difficulties inherent in analysing the resulting data. A broad overview of the methods of aligning individual shapes to remove the unwanted effects of location, rotation and scale is given, along with related geometrical issues in terms of the high-dimensional space in which a set of shapes resides. A general introduction to linear mixed effects models compares and contrasts them with simple linear models, explaining the reasons behind using them and presenting the different specifications of the conditional and marginal models. The area of dimension reduction is touched upon, specifically introducing B-splines and principal components analysis, with reference to the analysis of curves consisting of many points at small increments to one another. The data from the cleft-lip and palate study are introduced, along with a discussion of the primary interest of the analysis and the issue of missing data. Chapter 2 presents the statistical definition of a shape and introduces the area of statistical shape analysis in detail, specifically presenting the technicalities of shape space and distances, and methods such as Procrustes alignment of a set of shapes to remove unwanted effects. The concept of tangent coordinates is introduced as a projection of shape data into a Euclidean space, to enable the use of multivariate methods, and an outline given of thin-plate splines and deformations for the analysis of surfaces. Recent literature in the area of shape analysis is presented. Further recent literature addressing the modelling of growth in shapes is presented in Chapter 3, which goes on to discuss the use of linear mixed models on univariate and multivariate longitudinal data. The difficulties of applying mixed models to multivariate data are discussed and a recently proposed alternative method introduced, which involves fitting mixed models to the responses on pairs of outcomes rather than the full set. A description of the R function written as part of this thesis to fit such pairwise models follows, and this is applied to simulated triangles and quadrilaterals as an illustration. The initial application of the pairwise method to the cleft-lip and palate landmark data is presented in Chapter 4. The landmarks are described and the models are fitted to the tangent coordinate responses with different covariance structures for the random effects. The problems that arise and the deficiencies of the fitted models are extensively discussed. Chapter 5 goes on to address the issues raised in Chapter 4. A method of aligning the individual shapes based upon a subset of landmarks is suggested, along with a model that assumes independence of coordinates between dimensions but correlation within, and the benefits of these approaches compared. A simulation study is carried out to investigate the reasons behind and effects of random effects correlations that are estimated as being close to one, concluding that the problem lies in small variances that are poorly estimated, but that this is unlikely to be of severe detriment to the fixed effects estimates. A method of taking the principal components of the tangent coordinates is suggested, where the model responses are the principal components scores, and this proves to be the most appropriate way of applying the pairwise models in terms of model fit and computational efficiency. In Chapter 6, recent literature on the topic of curve analysis is presented, along with the way the facial curves are measured and the need for dimension reduction. Two methods are presented to this end: B-splines and principal components analysis, with the former suffering similar problems to the landmark analyses in terms of poorly estimated random effects variances, and the latter proving more successful. The application of the pairwise models to the principal components scores of the tangent coordinates provides a detailed analysis of the cleft-lip and palate data. Issues surrounding model comparison are addressed in Chapter 7, with several hypothesis tests presented and applied to simulated data. Drawbacks with some of the tests when applied to high dimensional or longitudinal data result in poor performance, but a method suggested by Faraway (1997) and a modification of the likelihood ratio test, both using bootstrapping, show similarly successful results. These are subsequently used to test for any differences in the time trends for the cleft and control groups post-surgery and find that there are significant differences. Condensed forms of this thesis have been presented at invited seminars and international conferences, and may be found in published form in Barry & Bowman (2006), Barry & Bowman (2007) and Barry & Bowman (2008).
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BUFFONI, SALETE SOUZA DE OLIVEIRA. "BUCKLING ANALYSIS OF LONGITUDINAL REINFORCEMENT IN CONCRETE COLUMNS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5517@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORA flambagem das armaduras longitudinais em pilares de concreto armado pode ocorrer na região entre dois estribos consecutivos, ou pode envolver um certo número de estribos. As normas de projeto existentes não fornecem uma metodologia apropriada para o dimensionamento dos estribos em diferentes situações. O presente trabalho tem por objetivo desenvolver uma formulação que permita analisar a flambagem das armaduras longitudinais em pilares de concreto armado submetidos a carregamento axial levando em conta o espaçamento entre os estribos, o diâmetro e arranjo dos estribos na seção transversal e o diâmetro das armaduras longitudinais. Para este propósito um método analítico para a avaliação da flambagem da armadura longitudinal é proposto, considerando-se as barras longitudinais restringidas pela rigidez axial ou à flexão dos estribos. Admite-se que a armadura longitudinal funciona como uma coluna esbelta. Consideram-se duas formas de modelagem da atuação dos estribos: como apoios elásticos discretos e como base elástica contínua. O presente trabalho trata a coluna com um ou mais modos de deformação, incluindo certas não- linearidades. São fornecidos cargas críticas e caminhos pós-críticos para tais casos. Como resultado deste estudo, apresenta-se uma proposta para dimensionamento racional dos estribos que permite estudar diferentes alternativas em um ábaco de utilização simples para projeto. Apresentam-se comparações com resultados experimentais da literatura em pilares de concreto armado. Isto permite uma avaliação crítica dos desenvolvimentos teóricos realizados e da forma proposta de dimensionamento racional dos estribos.
Buckling of longitudinal reinforcement in reinforced concrete columns may occur in the region between two consecutive ties, or may involve a number of ties. The existing design code specifications do not provide an appropriate methodology for the design of the transversal reinforcement in different situations. The main objective of the present work is to develop a formulation to allow to analyze the buckling of longitudinal bars in reinforced concrete columns taking into account the tie spacing, the diameter and arrangement of the ties in the cross section and the longitudinal bar diameter. For this purpose an analytical method for the evaluation of the buckling load of longitudinal bars is described, as a function of the constraint imposed by the axial or flexural stiffness of the stirrups. The longitudinal bar is considered as a column deforming according to thin beam theory. The tie action is described either by a set discrete elastic supports or by a continuous elastic foundation. The theoretical analysis considers the column with one or more deformation modes, with some degree of nonlinearity, including the analysis of post-critical equilibrium paths. As a result of this study, rational criteria for spacing and sizing of transversal reinforcement are derived, allowing to study different alternatives in an abacus of simple use for design. Several comparisons with the results obtained experimentally by other authors in reinforced concrete columns are presented, allowing for an evaluation of the validity of the theoretical developments and the rational design methodology proposed herein.
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Lee, Kang Qi Ian. "Computational tools for enabling longitudinal skin image analysis." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107060.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 165-174).
We present a set of computational tools that enable quantitative analysis of longitudinally acquired skin images: the assessment and characterization of the evolution of skin features over time. A framework for time-lapsed skin imaging is proposed. A nonrigid registration algorithm based on multiple plane detection for landmark identification accurately aligns pairs of longitudinal skin images. If dense and thick hairs are present, then nonrigid registration is used to reconstruct the skin texture of occluded regions by recording multiple images from the same area. Realistic reconstruction of occluded skin texture is aided by an automatic hair segmentation algorithm and guided painting method based on image blending. We demonstrate that constituent algorithms in this framework are accurate and robust in a multitude of scenarios. In addition, a methodology for rigorous longitudinal analysis of skin microrelief structure is introduced. Following rigid registration, a microrelief junction point matching algorithm based on point pattern matching is shown to accurately match two sets of junction points. Immediate applications for these computational tools are change detection for pigmented skin lesions and deformation field computation of the skin surface under stress using only visual features of the skin. Prospective applications include new insights in skin physiology and diseases from the capability to precisely track movements of the microrelief structure over time and localization of skin images on the body.
by Kang Qi Ian Lee.
S.M.