ABSTRACT: The t-Student distribution has been used to the spatial dependence modelling of soybean yield as an alternative to the normal distribution, being used for data with heavier tails or discrepant values. However, a usual Student t-distribution does not allow direct comparisons of geostatistical methods with a normal distribution. The aim of this study was to assess the soybean yield spatial variability through a reparameterized t-Student linear model, comparing the results with those of a Gaussian linear model. For parameter estimation, a complete maximum likelihood (CML) method was used through an expectation-maximization (EM) algorithm. The maps constructed with both reparameterized t-Student and normal distributions are dissimilar and present a kappa index (K) equivalent to 0.64. The reparameterized t-Student distribution is an alternative in studying data with discrepant values, showing the ability to decrease the influence of these points.

Objectives To identify retrospectively through chart analysis the biochemical recurrence frequency of localized prostate cancer at diagnosis of patients submitted to surgery or radiotherapy; to correlate diagnostic characteristics associated with higher risk of biochemical recurrence.Materials and Methods Retrospective analysis of 483 patients treated in a single center, from March 2000 to December 2009 in order to verify factors associated with biochemical recurrence.Results Biochemical recurrence was more frequent in patients with higher initial PSA levels and those with higher risk disease. Recurrence was more frequent in patients with high risk (25.9%) than those with intermediate risk (10.7%) and low risk (5.5%). There was no significant statistical difference of biochemical recurrence between patients submitted to radiotherapy or radical prostatectomy. Biochemical recurrence was diagnosed in only 11 of 73 patients (15%) submitted to conformal radiotherapy using tridimensional technique.Conclusion Radiotherapy and radical prostatectomy have similar treatment results. Tridimensional conformal radiotherapy used nowadays is more efficient than earlier forms of radiation therapy (cobalt therapy and bidimensional linear accelerator therapy).

O uso das ferramentas da geoestatística, aliadas à agricultura de precisão permitem o acompanhamento das áreas agrícolas produtoras de soja, estabelecendo as relações de dependência espacial entre os pontos amostrados. A modelagem da estrutura de variabilidade espacial possibilita a construção de mapas temáticos dos atributos estudados, utilizando como método de interpolação a krigagem. Porém, a presença de valores atípicos entre os elementos amostrais pode influenciar na construção e interpretação desses mapas. A distribuição de probabilidades t-Student tem sido utilizada na tentativa de diminuir a influência dos valores atípicos durante a estimativa dos parâmetros de dependência espacial, por ter caudas mais pesadas que a distribuição normal. A detecção dos valores influentes na área em estudo, por meio da análise de diagnósticos de influência local, confere maior confiabilidade na utilização dos mapas gerados, corroborando a aplicação de insumos. Deste modo, o objetivo deste trabalho foi aplicar as técnicas de influência local em dados espacialmente referenciados, com os modelos de perturbação aditiva e utilizando a matriz escala, considerando a distribuição t-Student n-variada. Foi utilizado um modelo espacial linear para o estudo de dados da produtividade da soja em função da altura média de plantas e do número médio de vagens por planta. As técnicas de influência local foram eficientes para detectar pontos que influenciam na escolha do modelo geoestatístico, nas estimativas dos parâmetros e na construção do mapa temático.

The use of geostatistical tools combined with precision agriculture, allow the monitoring of agricultural soybean producing areas, establishing relationships of spatial dependence between the sampled points. The modeling of spatial variability structure enables the construction of thematic maps of the attributes studied, using the kriging as the interpolation method. However, the presence of outliers among the elements sampling can influence the construction and interpretation of these maps. The distribution of t-Student probability has been used in attempts to reduce the influence of atypical points in the estimation of parameters of spatial dependence, having heavier tails than the normal distribution of probabilities. The detection of influential points in the study area, through the analysis of local influence diagnostics, provides greater reliability in the use of maps, providing an efficient use of inputs. Then, the objective was to apply the techniques of local influence on spatially referenced data with models of disturbance and using the matrix additive scale, considering the distribution t-Student n-variate. It was used a linear spatial model for the study of soybean yield data as a function of average plant height and number of pods per plant. The local influence techniques were effective to detect points that influence in the geostatistical model selection, estimation of parameters and construction of thematic maps.