• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 244
  • 50
  • 37
  • 18
  • 17
  • 11
  • 10
  • 10
  • 6
  • 6
  • 5
  • 3
  • 3
  • 3
  • 2
  • Tagged with
  • 497
  • 126
  • 98
  • 90
  • 75
  • 62
  • 42
  • 41
  • 37
  • 34
  • 32
  • 32
  • 31
  • 29
  • 29
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Nurse educators' perceptions of the implementation of recognition of prior learning in nursing colleges in Limpopo Province / Tinyiko Sophie Baloyi

Baloyi, Tinyiko Sophie January 2014 (has links)
Recognition of prior learning, better known as RPL, was introduced to training institutions in South Africa after the fall of Apartheid. The objective of RPL was to redress inequalities brought about by Apartheid when disadvantaged groups had less access to training opportunities. RPL was introduced with a combination of associated training and education initiatives such as the National Qualification Framework and the South African Qualifications Authority, all directed for a similar purpose. The South African Nursing Council agreed with the principles of RPL and published a policy document aimed to guide nurse educators to enhance RPL implementation in South African nursing education institutions. Despite the support from accessible legislative and regulatory documentation, RPL is implemented insufficiently in nursing education institutions. The lack of RPL implementation was also identified by the researcher in the Limpopo College of Nursing. This College of Nursing can be described as a symbol of post-Apartheid re-integration whereby nursing colleges centralised into one administrative management office with campuses, satellite campuses and over 120 nurse educators. The research question asked was what are nurse educators’ perceptions of the implementation of RPL in nursing colleges in Limpopo Province? The aim was to support nurse educators to enhance the implementation of RPL in nursing colleges in Limpopo Province. A qualitative, phenomenological, explorative, descriptive and contextual research design was followed. Seven (n=7) individual, in-depth, unstructured interviews were conducted with nurse educators employed at the X Campus and Y Satellite Campus of the Limpopo College of Nursing. Transcribed interviews were analysed and resulted in three main themes and nine sub-themes. Firstly, the participants voiced their agreement that RPL should be implemented and identified specific benefits and challenges thereof. Secondly, there should be a RPL assessment package that should be open and transparent, be able to assess academic performance against college standards and should minimise inequalities. The third main theme was the need for enhanced awareness of RPL implementation in nursing colleges. Nurse educators lack knowledge about RPL and should therefore be more awareness thereof. In addition RPL should be promoted as a beneficial mechanism to the learning process. These results were discussed with a literature integration and in the majority of results literature confirmed these findings. Conclusion statements were formulated from the research results and served as the basis for the formulation of recommendations to support nurse educators with the implementation of RPL in nursing colleges in Limpopo Province. The recommendations were directed to firstly the policy makers in nursing education; secondly to the nursing education institutions and thirdly to the nurse educators. Areas for further research were listed. Strategies to enhance trustworthiness and the adherence of ethical considerations were supported throughout this study. / MCur, North-West University, Potchefstroom Campus, 2014
202

”Vi behöver den specifika kunskapen, hur man fått den är faktiskt rätt ointressant” : En intervjustudie om validering av reell kompetens / ”We need the specific knowledge, how it is achieved is of less interest” : An Interview Study on Recognition of Prior Learning

Weinsjö, Anna, Lindh, Anders January 2016 (has links)
Den här studien syftar till att få ökad kunskap om på vilka sätt utbildningsanordnare inom yrkeshögskolan arbetar med validering av reell kompetens. Metoden som används är semistrukturerade kvalitativa intervjuer med sju personer som arbetar hos olika anordnare av yrkeshögskoleutbildningar. Med utgångspunkt i tidigare forskning om validering och olika perspektiv på kunskap, kompetens och lärande visar de viktigaste resultaten att informanterna ser reell kompetens som en möjlighet men hur informanterna synliggör den skiljer dem åt. Ett ständigt närvarande orosmoln för informanterna är att subjektiviteten påverkar tillförlitligheten vilket i sin tur påverkar rättssäkerheten i deras arbete. Studien belyser utmaningen att arbeta med validering av reell kompetens. Komplexiteten är stor vilket visar sig både i tolkning av centrala begrepp, subjektivitetens ständiga närvaro samt att informanterna efterfrågar tydliga riktlinjer och generaliserbara metoder. / The aim of this study is to increase the knowledge on how organizers of higher occupational educators work with recognition of prior learning (RPL). The method used is semi-structured interviews with seven professionals from seven different educational organizers of higher occupational education. With a starting point in earlier research and on different views on knowledge, competence and learning are the most interesting findings that the informants look upon recognition of prior learning as a possibility, but the way the informants visionalize RPL differs. An ongoing air of consciousness is how subjectivity influences the reliability, which in the next step can have a great impact of the legal rights of the individuals. The study stresses the challenge working with RPL. There is a great complexity shown in differences in interpreting central concepts and that the subjectivity is always present. The informants ask for guidelines and methods possible to generalize.
203

Régression logistique bayésienne : comparaison de densités a priori

Deschênes, Alexandre 07 1900 (has links)
La régression logistique est un modèle de régression linéaire généralisée (GLM) utilisé pour des variables à expliquer binaires. Le modèle cherche à estimer la probabilité de succès de cette variable par la linéarisation de variables explicatives. Lorsque l’objectif est d’estimer le plus précisément l’impact de différents incitatifs d’une campagne marketing (coefficients de la régression logistique), l’identification de la méthode d’estimation la plus précise est recherchée. Nous comparons, avec la méthode MCMC d’échantillonnage par tranche, différentes densités a priori spécifiées selon différents types de densités, paramètres de centralité et paramètres d’échelle. Ces comparaisons sont appliquées sur des échantillons de différentes tailles et générées par différentes probabilités de succès. L’estimateur du maximum de vraisemblance, la méthode de Gelman et celle de Genkin viennent compléter le comparatif. Nos résultats démontrent que trois méthodes d’estimations obtiennent des estimations qui sont globalement plus précises pour les coefficients de la régression logistique : la méthode MCMC d’échantillonnage par tranche avec une densité a priori normale centrée en 0 de variance 3,125, la méthode MCMC d’échantillonnage par tranche avec une densité Student à 3 degrés de liberté aussi centrée en 0 de variance 3,125 ainsi que la méthode de Gelman avec une densité Cauchy centrée en 0 de paramètre d’échelle 2,5. / Logistic regression is a model of generalized linear regression (GLM) used to explain binary variables. The model seeks to estimate the probability of success of this variable by the linearization of explanatory variables. When the goal is to estimate more accurately the impact of various incentives from a marketing campaign (coefficients of the logistic regression), the identification of the choice of the optimum prior density is sought. In our simulations, using the MCMC method of slice sampling, we compare different prior densities specified by different types of density, location and scale parameters. These comparisons are applied to samples of different sizes generated with different probabilities of success. The maximum likelihood estimate, Gelman’s method and Genkin’s method complement the comparative. Our simulations demonstrate that the MCMC method with a normal prior density centered at 0 with variance of 3,125, the MCMC method with a Student prior density with 3 degrees of freedom centered at 0 with variance of 3,125 and Gelman’s method with a Cauchy density centered at 0 with scale parameter of 2,5 get estimates that are globally the most accurate of the coefficients of the logistic regression.
204

Způsoby zadávání veřejných zakázek / Modes of public tenders

Herout, Štěpán January 2013 (has links)
The master's thesis is focused on the analysis of the conditions for use of particular modes of public tenders under the Act no. 137/2006 Coll., on Public Contracts, as amended. The main part of the thesis covers the negotiated procedure without prior notice, as the least transparent and yet frequently used type of award procedures. However, principal characteristics of all other types of award procedures are also mentioned. To provide a complete and sufficiently detailed analysis and comparison of particular types of award procedures, this thesis refers not only to doctrinal literature, but also to case law of the Office for the Protection of Competition, the Regional Court in Brno, the Supreme Administrative Court and also European case law. The thesis also includes analysis of selected provisions of Act no. 55/2012 Coll., effective as of 1 April 2012, significantly amending the Act on Public Contracts.
205

Meningsskapande samtal om fysikens begrepp : Att utgå från elevernas erfarenheter och förförståelse

Fritsch, Katarina January 2017 (has links)
Syftet med studien är att undersöka vad tidigare forskning säger om hur lärare kan organisera fysikundervisningen för att stödja elever, i årskurs 4 – 9, till meningsskapande samtal om fysikens begrepp. I denna systematiska litteraturstudie presenteras resultat utifrån litteratur som noggrant valts ut genom en systematisk sökningsprocess i databaserna Summon, ERIC, Nordina och avhandlingar.se där all litteratur har genomgått peer review. Studiens resultat visar att elever tillsammans bidrar till meningsskapande samtal genom att tillföra egna erfarenheter och förkunskaper om fysikens begrepp. Studien visar hur eleverna kan diskutera fritt så länge de har något att diskutera utifrån, exempelvis praktiska experiment, bilder, artefakter eller texter. Lärarens roll är sedan att stödja eleverna till att använda och förstå de korrekta vetenskapliga begreppen. Studien visar att läraren kan göra detta genom att koppla till vardagliga objekt och företeelser, ställa utmanande frågor, synliggöra nyckelbegrepp och elevers förförståelse samt återkoppla till elevers lärande. Med dessa olika metoder agerar läraren som en riktningsgivare som guidar eleven i en kunskapsutvecklande riktning. Genom att utgå från samt synliggöra elevernas förförståelse får både elever och lärare kunskap om eventuella missuppfattningar. Detta bidrar i sin tur till meningsskapande samtal då eleverna börjar ifrågasätta samt förändra och utveckla sin förståelse för fysiken begrepp.
206

Estimation Bayésienne de l’abondance par "removal sampling" en présence de variabilité du taux d’échantillonnage : application aux tiques Ixodes ricinus en quête d’hôtes / Bayesian estimation of abundance based on removal sampling with variability of the sampling rate : case study of questing Ixodes ricinus ticks

Bord, Séverine 17 June 2014 (has links)
L'estimation des abondances de population est essentielle pour comprendre les dynamiques de population, les interactions entre espèces et estimer les risques de transmission d'agents pathogènes dans les populations. Plusieurs méthodes d'échantillonnages, basées sur des hypothèses spécifiques permettent d'estimer ces abondances : les méthodes par comptages uniques, par « distance sampling », par échantillonnages successifs ou par capture marquage recapture. Nous nous sommes intéressés à l'abondance des tiques Ixodes ricinus, vecteurs de nombreux agents pathogènes. Cette abondance est classiquement estimée par le nombre de tiques capturées lors d'échantillonnages uniques réalisés sur différentes unités d'observation. Cependant, de nombreuses études remettent en cause cette hypothèse forte et suggèrent que le taux d'échantillonnage est variable selon les conditions d'échantillonnage (type de végétation,…) mais ne prennent pas en compte ce taux d'échantillonnage pour autant. A partir d'une méthode d'échantillonnage par « removal sampling » (RS), (i) nous avons montré que les conditions environnementales influençaient le taux d'échantillonnage et l'indicateur d'abondance usuel i.e. le nombre de tiques capturées lors d'un seul échantillonnage (ii) nous avons proposé une méthode pour détecter l'indicateur d'abondance, basés sur le nombre cumulé de capture, le moins soumis aux variations du taux ; (iii) par une approche Bayésienne hiérarchique, nous avons estimé simultanément l'abondance de tiques des unités d'observation et la valeur du taux d'échantillonnage en fonction du type de végétation et de l'heure d'échantillonnage. Nous avons montré que le taux d'échantillonnage sur des arbustes (entre 33,9 % et 47,4%) était significativement inférieur au taux d'échantillonnage sur des feuilles mortes (entre 53,6 % et 66,7%). De plus, nous avons montré que le modèle RS tend vers un modèle de Poisson iid lorsque la taille de la population N0 tend vers l'infini ce qui pose des problèmes d'indétermination pour estimer les paramètres N0 et τ, le taux d'échantillonnage. Nous avons également montré que (i) les estimateurs Bayésiens divergent lorsque les lois a priori sont des lois vagues ; (ii) les lois a priori β(a, b) avec a > 2 sur τ conduisaient à des estimateurs Bayésien convergents. Enfin, nous avons proposé des recommandations quant au choix des lois a priori pour τ afin d'obtenir de bonnes estimations pour N0 ou pour τ. Nous discutons de la pertinence des méthodes RS pour les tiques et des perspectives envisageables pour (i) estimer le risque acarologique représenté par la population de tiques potentiellement actives sur une unité d'observation, (ii) estimer un risque à l'échelle d'une parcelle, à savoir comment répartir l'effort d'échantillonnage entre le nombre d'unités d'observation et le nombre d'échantillonnages successifs par unités d'observation. / The estimation of animal abundance is essential to understand population dynamics, species interactions and disease patterns in populations and to estimate the risk of pathogens transmission. Several sampling methods such as single counts, distance sampling, removal sampling or capture mark recapture could be used to estimate abundance. In this study, we are investigated the abundance of Ixodes ricinus ticks, which are involved in the transmission of many pathogens. Tick abundance is commonly estimated by the number of nymphs captured during a single observation (a cloth dragged on a given surface). In this case, analyses of abundance patterns assumes that the probability of detecting a tick, hence the sampling rate, remains constant across the observations. In practice, however, this assumption is often not satisfied as the sampling rate may fluctuate between observation plots. The variation of sampling rate is never taken into account in estimations of tick abundance. Using a removal sampling design (RS), (i) we showed that the sampling rate and the usual abundance indicator (based on a single drag observation per spot) were both influenced by environmental conditions ; (ii) we proposed a method to determine the abundance indicator the least influenced by sampling rate variations ; (iii) using a hierarchical Bayesian model, we estimated simultaneously the abundance and the sampling rate according the type of vegetation, and the time of sampling. The sampling rate varied between 33,9 % and 47,4 % for shrubs and 53,6 % and 66,7 % for dead leaves. In addition, we show that the RS model tends to Poisson iid model when the population size N0 tends to infinite. This result conduct to infinite estimations for N0. We show that (i) Bayesian estimators were divergent for vague prior ; (ii) β(a, b) prior for a > 2 on τ conduct to convergent estimators. Then, we proposed recommendations for prior choice for τ parameter to give good estimations of N0 or τ. We discuss the relevance of RS for ticks and the possible perspectives to (i) estimate the acarologic risk associated to all potential active ticks for given spot, (ii) estimate the risk at the larger scale, i.e. how to distribute the sampling effort between number of spot and number of consecutive sampling by spot.
207

Assessing the use of a semisubmersible oil platform as a motion-based sea wave sensor. / Avaliação do uso de uma plataforma de óleo e gás do tipo semi-submersível como um sensor de onda marítimo baseado em movimento.

Soler, Jordi Mas 11 December 2018 (has links)
This thesis assesses the use of the measured motions of a semisubmersible oil platform as a basis for estimating on-site wave spectra. The inference method followed is based on the wave buoy analogy, which aims at solving the linear inverse problem: estimate the sea state, given the measured motions and the transfer function of the platform. Directional wave inference obtained from the records of vessels motions is a technique that has seen its application grow signicantly over the last years. As a matter of fact, its applications in ships with forward speed and ship-shaped moored platforms (such as FPSOs) have provided good results. However, little research has been done regarding the use of semisubmersible platforms as wave sensors. This is due to the fact that these platforms are designed to present no signicant responses when excited by waves. Notwithstanding this, the semisubmersible platforms are characterized by measurable small motions. Moreover, if compared with ship-shaped motion-based wave sensors, the responses of the semisubmersibles are in better agreement with the response characteristics estimations obtained by means of linear hydrodynamic models. In addition, the eminently linear characteristics of the responses often lasts even for severe wave conditions. This feature results in that the semisubmersible platforms stand as a promising wave sensor even for extreme sea states, conditions in which other types of sensors (i.e. buoys, radars) may face diculties. Throughout the text, the main results of this work are presented and discussed. These results are mainly based on a dedicated experimental campaign, carried out with a scaled model of the Asgar-B platform, which is a semisubmersible platform located in the Asgard eld oshore Norway. Regarding the sea states tested during the experiential campaign, they were estimated by means of a motion-based Bayesian inference method, which has been developed for more than then years at the EPUSP. In order to allow the adoption of the semisubmersible platforms as a motion based wave sensors, this thesis provides two signicant improvements of the method: rst, a method to obtain an estimation of the linearized equivalent external viscous damping is provided. This analytical methodology allows to reduce the uncertainty of the transfer function of the platform close to the resonances of the motions and, as a consequence, it increases the accuracy of the inference approach. The second relevant contribution is the development of an alternative prior distribution, which is adopted to introduce the prior beliefs regarding the sea state in the Bayesian inference approach. It is shown that although some aspects of this novel approach require further evaluation in future work, the prior distribution developed has potential to improve the accuracy of wave estimates, and, at the same time, it signi cantly simplies the calibration procedures followed by other state-of-the-art Bayesian wave inference methods. Summing up, the inference approach proposed in this work provides the bases to use each semisubmersible oil platform, which stand as the most common type of oil platforms operated oshore Brasil, as a motion based wave sensor, thus contributing to the possible broadening of the Brazilian oceanographic measurement network. / A presente tese investiga a adoção de plataformas de petróleo semi submersíveis como base para inferência das condições de onda através do monitoramento de seus movimentos. O problema em questão consiste na solução do problema inverso de comportamento em ondas; ou seja, uma vez observados os movimentos da unidade flutuante (e conhecidas suas funções de resposta de movimento), estima-se as condições de ondas que os causaram. Este tipo de método já vem sendo empregado há anos para navios em curso e também para navios convertidos em plataformas de petróleo (os chamados FPSOs) com bons resultados. No entanto, o possível emprego de plataformas semi-submersíveis para o mesmo fim foi muito pouco explorado até o momento. Evidentemente, isso decorre da suposição de que, uma vez que essas estruturas são projetadas com o intuito primeiro de atenuar os movimentos decorrentes das ações de ondas, naturalmente elas não seriam bons sensores para esta finalidade. Os resultados apresentados nesta tese, todavia, contrariam tal suposição. De fato, as semi-submersíveis respondem de forma fraca as ondas, porem esta resposta é mensurável. Não apenas isso, mas, em comparação com os cascos de navios, esta resposta adere melhor às previsões dos modelos hidrodinâmicos lineares a partir dos quais as características da plataforma são estimadas. Ademais, o caráter eminentemente linear da resposta muitas vezes perdura inclusive para condições de ondas severas. Isto, por sua vez, torna as semi-submersíveis promissoras inclusive para a estimação de mares extremos, situação nas quais os outros tipos de sensores (boias, radares) enfrentam dificuldades. Nesta tese, a demonstração destes fatos é sustentada por um extenso conjunto de testes experimentais realizados em tanque de ondas com um modelo em escala reduzida de uma plataforma que hoje opera no Mar do Norte. Para tanto, foi empregado um método de inferência Bayesiana para estimação de ondas em navios que vem sendo desenvolvido na EPUSP há mais de dez anos. Para o estudo das semi-submersíveis o trabalho propõe duas melhorias importantes no método: A primeira consiste em um procedimento analítico para prever o amortecimento hidrodinâmico de origem viscosa dos movimentos observados do casco. Este procedimento permite reduzir as incertezas quanto a função de resposta em condições de ressonância dos movimentos com as ondas e, dessa forma, aumentar a confiabilidade do método. A segunda contribuição relevante é a proposição de uma alternativa para a chamada distribuição a priori originalmente empregada pelo método Bayesiano. Demonstra-se que, embora alguns aspectos desta nova metodologia ainda necessitem de uma avaliação adicional em trabalhos futuros, a nova distribuição tem grande potencial para melhorar a precisão das estimativas de ondas, além de simplificar de maneira significativa os procedimentos atuais de calibração do sistema de inferência. Em suma, o método de inferência aqui proposto abre caminho para tornar cada unidade flutuante de óleo e gás do tipo semi-submersível, um dos sistemas de produção mais frequentes nas costas brasileiras, um eventual ponto de monitoramento de ondas, contribuindo então para a possível ampliação de nossas bases de medição oceanograficas.
208

Vieillissement cognitif et connaissances antérieures dans la recherche d'informations : étude des processus cognitifs et implications ergonomiques / Cognitive aging and prior knowledge in information search : cognitive processes involed and ergonomics implications

Sanchiz, Mylène 04 December 2017 (has links)
Rechercher de l’information sur Internet avec un moteur de recherche est une activité complexe qui exige des utilisateurs un grand nombre de traitements. Les travaux de recherche sur les effets du vieillissement en RI ont montré que les utilisateurs âgés ont de moins bonnes performances, passent plus de temps à évaluer les pages de résultats du moteur de recherche et reformulent moins que les jeunes. Ces difficultés seraient dues au déclin des habiletés cognitives fluides comme la flexibilité cognitive, la vitesse de traitement ou le rafraichissement en mémoire de travail. Pour comprendre comment le vieillissement cognitif affecte l’activité de RI, nos travaux ont investigué les stratégies de recherche élaborées par les utilisateurs jeunes et âgés ainsi que les processus cognitifs impliqués. La première partie de ce travail s’est attaché à étudier, au travers de 2 expérimentations, comment les connaissances antérieures peuvent soutenir l’activité de recherche des utilisateurs plus âgés et les aider à répondre aux exigences de la RI selon le niveau de complexité des tâches de recherche. La deuxième partie du travail de recherche a investigué le rôle de deux dispositifs d’aide à la RI : l’un maximisant les effets bénéfiques des connaissances antérieures par un dispositif de pré-activation (étude 3), et l’autre soutenant le maintien du but en mémoire de travail (étude 4). Nos résultats ont montré que les utilisateurs plus âgés ont davantage de difficultés que les jeunes à évaluer les pages de résultats du moteur de recherche et à reformuler leurs requêtes (ils produisent moins de nouveaux mots clés et utilisent plus de mots clés issus des problèmes de recherche). En outre, la phase initiale de l’activité de recherche s’est avérée être plus critique pour les adultes âgés qui produisent des requêtes initiales moins élaborées et passent plus de temps sur la première page de résultats du moteur de recherche. Les connaissances antérieures sur le domaine peuvent toutefois soutenir le niveau d’élaboration des requêtes des utilisateurs plus âgés et améliorer les stratégies de recherche. Par ailleurs, pré-activer les connaissances antérieures peut soutenir l’élaboration de stratégies de recherche descendantes et améliorer le contenu sémantique des requêtes des âgés (particulièrement dans un domaine pour lequel ils ont de faibles connaissances antérieures). Enfin, l’outil d’aide soutenant le maintien du but en mémoire de travail favorise des stratégies de recherche plus flexibles en améliorant la reformulation des requêtes (temps de reformulation plus courts) et en aidant l’exploration en début d’activité. Ces travaux de recherche posent les bases d’un nouveau modèle cognitif de l’activité des RI pour les utilisateurs plus âgés. / Searching for information with a search engine is a complex activity that requires users to perform a series of cognitive processes. Prior works showed that older users can have lower search performance, they spent more time on the search engine result pages and they produce fewer queries than young ones. Older users’ difficulties are mainly caused by the age-related decline of fluid abilities such as cognitive flexibility, processing speed or update in working memory. To understand the effects of aging on information search with a search engine, we studied the search strategies elaborated and the cognitive processes involved by young and older adults. The first part of the present work investigated how prior knowledge about the search topic can support older users’ on-line search behavior and help them deal with the search task complexity (2 experiments). The second part of our work analyzed the role of two information search support tools. One tool aimed at optimizing the benefits of domain knowledge by pre-activating prior knowledge (experiment 3) whereas the other aimed at supporting search goal refreshing in working memory (experiment 4). Results showed that older users had more difficulties evaluating the search engine results pages and reformulating than young ones (i.e. they produced fewer new keywords and used more keywords extracted from the search problem statement in their queries). The initial stage of the search represented a challenge for older users who formulated initial queries that were less elaborate and spent longer dwell time on the first search engine page than young ones. Prior knowledge can improve older users’ reformulation and support more elaborate search strategies. In addition, pre-activating prior knowledge can foster top-down search strategies and improve the semantic content of the queries produced by older users (especially in a domain for which they have low prior knowledge). The support tool helping search goal refreshing in working memory fostered more flexible search strategies and improved reformulation (i.e. reduced the time needed by older users to reformulate). Eventually, our research work led us to elaborate a new cognitive model of information search with a search engine that takes into account the role of aging.
209

Bayesian approaches for the analysis of sequential parallel comparison design in clinical trials

Yao, Baiyun 07 November 2018 (has links)
Placebo response, an apparent improvement in the clinical condition of patients randomly assigned to the placebo treatment, is a major issue in clinical trials on psychiatric and pain disorders. Properly addressing the placebo response is critical to an accurate assessment of the efficacy of a therapeutic agent. The Sequential Parallel Comparison Design (SPCD) is one approach for addressing the placebo response. A SPCD trial runs in two stages, re-randomizing placebo patients in the second stage. Analysis pools the data from both stages. In this thesis, we propose a Bayesian approach for analyzing SPCD data. Our primary proposed model overcomes some of the limitations of existing methods and offers greater flexibility in performing the analysis. We find that our model is either on par or, under certain conditions, better, in preserving the type I error and minimizing mean square error than existing methods. We further develop our model in two ways. First, through prior specification we provide three approaches to model the relationship between the treatment effects from the two stages, as opposed to arbitrarily specifying the relationship as was done in previous studies. Under proper specification these approaches have greater statistical power than the initial analysis and give accurate estimates of this relationship. Second, we revise the model to treat the placebo response as a continuous rather than a binary characteristic. The binary classification, which groups patients into “placebo-responders” or “placebo non-responders”, can lead to misclassification, which can adversely impact the estimate of the treatment effect. As an alternative, we propose to view the placebo response in each patient as an unknown continuous characteristic. This characteristic is estimated and then used to measure the contribution (or the weight) of each patient to the treatment effect. Building upon this idea, we propose two different models which weight the contribution of placebo patients to the estimated second stage treatment effect. We show that this method is more robust against the potential misclassification of responders than previous methods. We demonstrate our methodology using data from the ADAPT-A SPCD trial.
210

From here to infinity: sparse finite versus Dirichlet process mixtures in model-based clustering

Frühwirth-Schnatter, Sylvia, Malsiner-Walli, Gertraud January 2019 (has links) (PDF)
In model-based clustering mixture models are used to group data points into clusters. A useful concept introduced for Gaussian mixtures by Malsiner Walli et al. (Stat Comput 26:303-324, 2016) are sparse finite mixtures, where the prior distribution on the weight distribution of a mixture with K components is chosen in such a way that a priori the number of clusters in the data is random and is allowed to be smaller than K with high probability. The number of clusters is then inferred a posteriori from the data. The present paper makes the following contributions in the context of sparse finite mixture modelling. First, it is illustrated that the concept of sparse finite mixture is very generic and easily extended to cluster various types of non-Gaussian data, in particular discrete data and continuous multivariate data arising from non-Gaussian clusters. Second, sparse finite mixtures are compared to Dirichlet process mixtures with respect to their ability to identify the number of clusters. For both model classes, a random hyper prior is considered for the parameters determining the weight distribution. By suitable matching of these priors, it is shown that the choice of this hyper prior is far more influential on the cluster solution than whether a sparse finite mixture or a Dirichlet process mixture is taken into consideration.

Page generated in 0.057 seconds