Persona: García Pérez, Alfonso
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García Pérez
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Publicación Robust morphometric analysis based on landmarks(Springer, 2018-03-01) García Pérez, AlfonsoProcrustes Analysis is a Morphometric method based on Configurations of Landmarks that estimates the superimposition parameters by least-squares; for this reason, the procedure is very sensitive to outliers. There are classical results, based on the normality of the observations, to test whether there are significant differences between individuals. In this paper we determine a Von Mises plus Saddlepoint approximation for the tail probability (p-value) of this test for the Procrustes Statistic, when the observations come from a model close to the normal.Publicación Saddlepoint approximations for the distribution of some robust estimators of the variogram(Springer, 2019-06-26) García Pérez, AlfonsoIn this paper, we obtain a saddlepoint approximation for the small sample distribution of several variogram estimators such as the classical Matheron’s estimator, some M-estimators like the robust Huber’s variogram estimator, and also the α-trimmed variogram estimator. The tail probability approximation obtained is very accurate even for small sample sizes. In the approximations we consider that the observations follow a distribution close to the normal, specifically, a scale contaminated normal model. To obtain the approximations we transform the original observations into a new ones, which can be considered independent if a linearized variogram can be accepted as model for them. To check this, a goodness of fit test for a variogram model is defined in the last part of the paper.