Methods of testing for a location shift between two populations in a longitudinal study are investigated when the data of interest are ordered, categorical and non-linear. A non-standard analysis involving modelling of data over time with transition probability matrices is discussed. Next, the relative efficiencies of statistics more frequently used for the analysis of such categorical data at a single time point are examined. The Wilcoxon rank sum, McCullagh, and 2 sample t statistic are compared for the analysis of such cross sectional data using simulation and efficacy calculations. Simulation techniques are then utilized in comparing the stratified Wilcoxon, McCullagh and chi squared-type statistic in their efficiencies at detecting a location shift when the data are examined over two time points. The distribution of a chi squared-type statistic based on the simple contingency table constructed by merely noting whether a subject improved, stayed the same or deteriorated is derived. Applications of these methods and results to a data set of Multiple Sclerosis patients, some of whom were treated with interferon and some of whom received a placebo are provided throughout the thesis and our findings are summarized in the last Chapter. / Science, Faculty of / Statistics, Department of / Graduate

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Orientador: Marcela Aparecida Guerreiro Machado de Freitas / Coorientador: Roberto Campos Leoni / Banca: Félix Monteiro Pereira / Banca: Nilo Antônio de Souza Sampaio / Resumo: A produção leiteira é destaque entre os principais produtos agropecuários por ser um alimento altamente empregado na dieta humana e uma atividade que gera emprego e renda. Inúmeros fatores tornam a produção leiteira muito heterogênea, dentre os quais destacam-se: o tamanho das propriedades, a tecnologia empregada na atividade leiteira e o nível de conhecimento dos produtores. O objetivo desta pesquisa foi identificar os fatores que interferem na produção leiteira da microrregião Sudeste do Estado de Roraima e propor a formação de agrupamentos homogêneos de produtores locais. O método empregado para o desenvolvimento deste trabalho estabeleceu a identificação dos fatores potenciais que interferem na produção leiteira a partir de uma revisão da literatura; construção de um questionário com os fatores potenciais que interferem na produtividade e qualidade do leite; entrevistas com aplicação de questionário; análises estatísticas descritiva e análises de agrupamentos. Na análise descritiva, obtiveram-se tabelas com análise de frequência e buscou-se comparar com os dados obtidos em outros trabalhos. Na análise de agrupamentos, empregou-se a classificação hierárquica, método de Ward e coeficiente de distância Gower. Verificou-se que as propriedades visitadas se caracterizam como estabelecimentos de produção de base familiar e produção de subsistência; quanto à formação de agrupamentos de produtores, identificaram-se sete agrupamentos, quantidade que se assemelha a realidade local, ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Milk production is among the most relevant agricultural and livestock products due to its importance as a type of food that is highly used in human diets and as an activity that generates jobs and income. Countless factors make milk production very heterogeneous, among which are property size, technology used in milking activities, and the level of knowledge of producers. The objective of the present study was to identify factors that interfere in milk production of the southeastern microregion of the state of Roraima and propose the creation of homogeneous clusters of local producers. The methodological approach used in this study involved a literature review to identify potential factors that interfere in milk production; the construction of a questionnaire with these potential factors that interfere in milk productivity and quality; interviews applying the questionnaire; and descriptive statistical and cluster analyses. The descriptive analysis yielded tables of frequency analysis results and allowed comparisons and correlations of data obtained in other studies. In turn, the cluster analysis was conducted using a hierarchical classification, Ward's method, and Gower's distance coefficient. The properties visited in the present study were characterized as family-based production and subsistence production establishments. In total, 7 producer clusters were identified, which was consistent with local reality, since the region does not present a standardized profile of milkin... (Complete abstract click electronic access below) / Mestre

A research project submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering, 2018. / The power system inertia immediately following small and large system disturbances was investigated. By understanding factors affecting the system inertia and primary frequency response behaviour, an online inertia model was developed. Historical data was extracted from the Eskom Energy Management System (EMS) and Wide Area Monitoring System (WAMS). The developed model using Multivariate Analysis (MVA) includes measured and estimated data from Eskom generators, Renewable Energy Sources (RESs) and the interconnected Southern African Power Pool (SAPP). Inertia plus Fast Primary (Frequency) Response (FPR) (as determined by the load behaviour) and system inertia models were developed from June 2015-December 2016 and validated with past frequency disturbance events (June 2014-March 2017). From the comparison between the measured and model results for 355 actual disturbances, 225 disturbances resulted in errors within ±5% and 51 events resulted in errors between ±5% and ±10%. Eight disturbances caused errors greater than ±10%, which were largely from trips at particular large power stations and HVDC. During a large disturbance, the multivariate coefficients for Renewable Energy Sources, HVDC and interconnectors were very small for the pure inertia model (excluding the load frequency behaviour and the generator damping). In contrast, the spinning reserve provides significant contribution and is location based. The location of a disturbance affects the FPR behaviour and the system inertia but not the Rate of Change of Frequency (RoCoF) with reference to the central power station. The strong and weak areas with respect of the stiffness of the system (extent of frequency nadir for particular disturbances) were identified. This can contribute to future grid planning and real-time operations in managing the system inertia and primary frequency response. The model is expected to improve with time, as the accuracy of a statistical approach requires large amounts of data. The model can be used to determine and monitor the maximum level of RES in real time. / XL2019

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