Exact and heuristic algorithms for variable selection: Extended Leaps and Bounds

An implementation of enhanced versions of the classical Leaps and Bounds algorithm for variable selection is provided. Features of this implementation include: (i) The availability of general routines capable of handling many different statistical methodologies and comparison criteria. (ii) Routines designed for exact and heuristic searches. (iii) The possibility of dealing with problems with more variables than observations. The implementation is supplied in two different ways: i) as a C++ library with abstract classes that can be specialized to different problems and criteria. ii) as a console application ready to be applied to searches according to some of the most important comparison criteria proposed to date. The code of the C++ library and console application described here, can be freely obtained by sending an email to the author.Variable Selection Algorithms; All-Subsets; Heuristics

Efficient screening of variable subsets in multivariate statistical models

info:eu-repo/semantics/publishedVersio

Exact and heuristic algorithms for variable selection: Extended Leaps and Bounds

An implementation of enhanced versions of the classical Leaps and Bounds algorithm for variable selection is provided. Features of this implementation include: (i) The availability of general routines capable of handling many different statistical methodologies and comparison criteria. (ii) Routines designed for exact and heuristic searches. (iii) The possibility of dealing with problems with more variables than observations. The implementation is supplied in two different ways: i) as a C++ library with abstract classes that can be specialized to different problems and criteria. ii) as a console application ready to be applied to searches according to some of the most important comparison criteria proposed to date. The code of the C++ library and console application described here, can be freely obtained by sending an email to the authorinfo:eu-repo/semantics/publishedVersio

DISCARDING VARIABLES in PRINCIPAL COMPONENT ANALYSIS : ALGORITHMS for ALL-SUBSETS COMPARISONS

The traditional approach to the interpretation of the results from a Principal Component Analysis implicitly discards variables that are weakly correlated with the most important and/or most interesting Principal Components. Some authors argue that this practice is potentially misleading and that it would be preferable to take a variable selection approach comparing variable subsets according to appropriate approximation criteria. In this paper, we propose algorithms for the comparison of all possible subsets according to some of the most important criteria proposed to date. The computational effort of the proposed algorithms is studied and it is shown that, given current computer technology, they are feasible for problems involving up to 30 variables. A software implementation is freely available on the internet.Principal Component Analysis, Principal Variables, Variable Selection, All-Subsets Algorithms.

Two-group classification in business: an evaluation of parametric and non-parametric approaches

info:eu-repo/semantics/publishedVersio

Probabilistic clustering of interval data

In this paper we address the problem of clustering interval data, adopting a model-based approach. To this purpose, parametric models for interval-valued variables are used which consider configurations for the variance-covariance matrix that take the nature of the interval data directly into account. Results, both on synthetic and empirical data, clearly show the well-founding of the proposed approach. The method succeeds in finding parsimonious heterocedastic models which is a critical feature in many applications. Furthermore, the analysis of the different data sets made clear the need to explicitly consider the intrinsic variability present in interval data.info:eu-repo/semantics/publishedVersio

Primeiro registo do tubarão-anão, Squaliolus laticaudus (Smith & Radcliffe, 1912) nos Açores, estendendo a sua distribuição ocidental no Atlântico Nordeste

A presente nota documenta a primeira observação do tubarão-anão, Squaliolus laticaudus (Smith & Radcliffe, 1912), nos Açores, estendendo a sua distribuição ocidental no Atlântico Nordeste até ao arquipélago. A ocorrência da espécie nos arquipélagos macaronésicos é igualmente discutida.ABSTRACT: This paper reports the first observation of the spined pygmy shark, Squaliolus laticaudus, from the Azores, extending its westernmost distribution in the North-eastern Atlantic as far as this archipelago. The occurrence of this species in the Macaronesian archipelagos is also discussed

Staining techniques for ageing tope shark, Galeorhinus galeus (Linnaeus, 1758), from the Azores : a comparison based on precision analysis.

A vertebrae sample of tope shark, Galeorhinus galeus (Linnaeus, 1758), stratified by sizeclasses,was used to test between different staining techniques of enhancing vertebral growth ring visibility. Four techniques were tested: alizarin red, silver nitrate and cobalt nitrate staining, and the “deep-coned vertebrae” technique. The latter was discarded due to its unsuitability for tope shark vertebrae. The cobalt nitrate original protocol was modified. Upon staining, each vertebra was subject to three replicated independent readings, by a single reader. Within-reader consistency and bias of growth ring counts determination were evaluated using four different precision indices: percent of agreement (PA), average percent error (APE), coefficient of variation (V) and index of precision (D). Results indicated that the vertebrae stained with the cobalt nitrate technique showed both better optic enhancement of growth rings and higher degree of count consistency, comparatively to the alizarin red and silver stained vertebrae. Conclusively, the cobalt nitrate was the most efficient staining technique upon tope shark vertebrae, among the methods tested herein