Meaning of the λ parameter of skew–normal and log–skew normal distributions in fluid geochemistry
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The literature related to skew–normal distributions has grown rapidly in recent years
but at the moment few applications concern the description of natural phenomena with
this type of probability models, as well as the interpretation of their parameters. The
skew–normal distributions family represents an extension of the normal family to which
a parameter (λ) has been added to regulate the skewness. The development of this theoretical
field has followed the general tendency in Statistics towards more flexible methods
to represent features of the data, as adequately as possible, and to reduce unrealistic
assumptions as the normality that underlies most methods of univariate and multivariate
analysis. In this paper an investigation on the shape of the frequency distribution of the
logratio ln(Cl−/Na+) whose components are related to waters composition for 26 wells,
has been performed. Samples have been collected around the active center of Vulcano
island (Aeolian archipelago, southern Italy) from 1977 up to now at time intervals of
about six months. Data of the logratio have been tentatively modeled by evaluating the
performance of the skew–normal model for each well. Values of the λ parameter have
been compared by considering temperature and spatial position of the sampling points.
Preliminary results indicate that changes in λ values can be related to the nature of
environmental processes affecting the data
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