Quinze anys d'Universitat

Breu repàs històric dels 15 anys de la Universitat amb les paraules dels rectors

La MAT encén el debat de l'energia a Girona

Opinions sobre el projecte de línia de molt alta tensió a les comarques gironines i anàlisi de l'impacte ambiental

Història urbana de Girona: una història dibuixada

El Dr. Josep Maria Nolla ha contribuït de manera decisiva al coneixement dels orígens de la ciutat de Girona. El seu treball i el dels seus companys en aquesta aventura de recerca és a l'abast de tothom en la col·lecció "Història urbana de Girona", que ha tingut, la tardor del 2007, una traducció brillant en l'exposició "De Kerunta a Gerunda. Els orígens de la ciutat"

Biotech Girona: l'espai de la biotecnologia

Espais a mida, tota mena de facilitats i bona companyia. Sembla l'anunci d'una promoció immobiliària, però això és el que ofereix el Biogech Girona, un lloc dins el Parc Científic i Tecnològic que proposa espais a mida per establir-se en un entorn d'excel·lència en la recerca. El Parc acaba d'obrir la convocatòria per seleccionar les empreses interessades

Batxillerat: camins cap a la Universitat

El batxillerat és un intens camí que recorre l'estudiant i que en bona part dels casos té com a meta la universitat. En el trajecte hi ha uns quants esculls, com el treball de recerca i la selectivitat. Els joves han de prémer fort l'accelerador si volen assolir la fita consignada. El suport de la família i els professors els pot fer el viatge una mica més fàcil

Medicina a Girona

La Universitat de Girona impartirà la titulació de Medicina en una facultat pròpia a partir del curs 2008-2009. Es proposa un pla d'estudis innovador que la convertirà en un centre pioner a Catalunya, elaborat en complicitat amb els diversos agents clínics i assistencials de la demarcació, per garantir la màxima qualitat de la docència i la recerca

Física bàsica per a la universitat [versió html]

Llibre preparat per ser utilitzat com a material de text de Física bàsica, assignatura de lliure elecció de 6 crèdits, del segon quadrimestre dels nous plans d'estudis d' Informàtica Tècnica (especialitats de Sistemes i de Gestió) i d' Enginyeria Tècnica Agrícola (especialitats d' Explotacions Agropecuàries i d' Indústries Agràries i Agroalimentàries) de la Universitat de Girona. L’objectiu estratègic és donar als alumnes, en un sol quadrimestre, la formació necessària per a seguir un curs de primer de física, així com que l’alumne tingui agilitat en la transformació d’unitats, s’habituï a comprovar la raonabilitat dels resultats i sigui capaç de superar la noció que la física és un conjunt de formules inconnexes

Introducció a l'estadística aplicada per a educadors [versió html]

Es tracta d’un material docent, amb què s’intenta facilitar als estudiants del camp de l’educació l’aprenentatge dels fonaments de l’estadística descriptiva i aplicada. Aquesta publicació vol ajudar a comprendre els conceptes bàsics per utilitzar-los amb seguretat en contextos de recerca i per entendre les dades d’estudis educatius i socials. El document està organitzat en cinc apartats i cada apartat conté una explicació sobre el concepte o conceptes que s’hi treballen, un o dos exemples d’exercicis desenvolupats, propostes d’exercicis i les respostes a aquests exercicis. Finalment, hi ha un sisè capítol amb exercicis de recopilació

Some last thoughts on compositional data analysis

One of the disadvantages of old age is that there is more past than future: this, however, may be turned into an advantage if the wealth of experience and, hopefully, wisdom gained in the past can be reflected upon and throw some light on possible future trends. To an extent, then, this talk is necessarily personal, certainly nostalgic, but also self critical and inquisitive about our understanding of the discipline of statistics. A number of almost philosophical themes will run through the talk: search for appropriate modelling in relation to the real problem envisaged, emphasis on sensible balances between simplicity and complexity, the relative roles of theory and practice, the nature of communication of inferential ideas to the statistical layman, the inter-related roles of teaching, consultation and research. A list of keywords might be: identification of sample space and its mathematical structure, choices between transform and stay, the role of parametric modelling, the role of a sample space metric, the underused hypothesis lattice, the nature of compositional change, particularly in relation to the modelling of processes. While the main theme will be relevance to compositional data analysis we shall point to substantial implications for general multivariate analysis arising from experience of the development of compositional data analysis…

Conditional compositional biplots: theory and application

The biplot has proved to be a powerful descriptive and analytical tool in many areas of applications of statistics. For compositional data the necessary theoretical adaptation has been provided, with illustrative applications, by Aitchison (1990) and Aitchison and Greenacre (2002). These papers were restricted to the interpretation of simple compositional data sets. In many situations the problem has to be described in some form of conditional modelling. For example, in a clinical trial where interest is in how patients’ steroid metabolite compositions may change as a result of different treatment regimes, interest is in relating the compositions after treatment to the compositions before treatment and the nature of the treatments applied. To study this through a biplot technique requires the development of some form of conditional compositional biplot. This is the purpose of this paper. We choose as a motivating application an analysis of the 1992 US President ial Election, where interest may be in how the three-part composition, the percentage division among the three candidates - Bush, Clinton and Perot - of the presidential vote in each state, depends on the ethnic composition and on the urban-rural composition of the state. The methodology of conditional compositional biplots is first developed and a detailed interpretation of the 1992 US Presidential Election provided. We use a second application involving the conditional variability of tektite mineral compositions with respect to major oxide compositions to demonstrate some hazards of simplistic interpretation of biplots. Finally we conjecture on further possible applications of conditional compositional biplots

Meaning of the λ parameter of skew–normal and log–skew normal distributions in fluid geochemistry

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

Assessing the Precision of Compositional Data in a Stratified Double Stage Cluster Sample: Application to the Swiss Earnings Structure Survey

Precision of released figures is not only an important quality feature of official statistics, it is also essential for a good understanding of the data. In this paper we show a case study of how precision could be conveyed if the multivariate nature of data has to be taken into account. In the official release of the Swiss earnings structure survey, the total salary is broken down into several wage components. We follow Aitchison's approach for the analysis of compositional data, which is based on logratios of components. We first present diferent multivariate analyses of the compositional data whereby the wage components are broken down by economic activity classes. Then we propose a number of ways to assess precision

A compositional approach to stable isotope data analysis

Isotopic data are currently becoming an important source of information regarding sources, evolution and mixing processes of water in hydrogeologic systems. However, it is not clear how to treat with statistics the geochemical data and the isotopic data together. We propose to introduce the isotopic information as new parts, and apply compositional data analysis with the resulting increased composition. Results are equivalent to downscale the classical isotopic delta variables, because they are already relative (as needed in the compositional framework) and isotopic variations are almost always very small. This methodology is illustrated and tested with the study of the Llobregat River Basin (Barcelona, NE Spain), where it is shown that, though very small, isotopic variations comp lement geochemical principal components, and help in the better identification of pollution sources

CODAPACK3D. A new version of Compositional Data Package

The statistical analysis of compositional data should be treated using logratios of parts, which are difficult to use correctly in standard statistical packages. For this reason a freeware package, named CoDaPack was created. This software implements most of the basic statistical methods suitable for compositional data. In this paper we describe the new version of the package that now is called CoDaPack3D. It is developed in Visual Basic for applications (associated with Excel©), Visual Basic and Open GL, and it is oriented towards users with a minimum knowledge of computers with the aim at being simple and easy to use. This new version includes new graphical output in 2D and 3D. These outputs could be zoomed and, in 3D, rotated. Also a customization menu is included and outputs could be saved in jpeg format. Also this new version includes an interactive help and all dialog windows have been improved in order to facilitate its use. To use CoDaPack one has to access Excel© and introduce the data in a standard spreadsheet. These should be organized as a matrix where Excel© rows correspond to the observations and columns to the parts. The user executes macros that return numerical or graphical results. There are two kinds of numerical results: new variables and descriptive statistics, and both appear on the same sheet. Graphical output appears in independent windows. In the present version there are 8 menus, with a total of 38 submenus which, after some dialogue, directly call the corresponding macro. The dialogues ask the user to input variables and further parameters needed, as well as where to put these results. The web site http://ima.udg.es/CoDaPack contains this freeware package and only Microsoft Excel© under Microsoft Windows© is required to run the software. Kew words: Compositional data Analysis, Software

News from compositions, the R package

The R-package “compositions”is a tool for advanced compositional analysis. Its basic functionality has seen some conceptual improvement, containing now some facilities to work with and represent ilr bases built from balances, and an elaborated subsys- tem for dealing with several kinds of irregular data: (rounded or structural) zeroes, incomplete observations and outliers. The general approach to these irregularities is based on subcompositions: for an irregular datum, one can distinguish a “regular” sub- composition (where all parts are actually observed and the datum behaves typically) and a “problematic” subcomposition (with those unobserved, zero or rounded parts, or else where the datum shows an erratic or atypical behaviour). Systematic classification schemes are proposed for both outliers and missing values (including zeros) focusing on the nature of irregularities in the datum subcomposition(s). To compute statistics with values missing at random and structural zeros, a projection approach is implemented: a given datum contributes to the estimation of the desired parameters only on the subcompositon where it was observed. For data sets with values below the detection limit, two different approaches are provided: the well-known imputation technique, and also the projection approach. To compute statistics in the presence of outliers, robust statistics are adapted to the characteristics of compositional data, based on the minimum covariance determinant approach. The outlier classification is based on four different models of outlier occur- rence and Monte-Carlo-based tests for their characterization. Furthermore the package provides special plots helping to understand the nature of outliers in the dataset. Keywords: coda-dendrogram, lost values, MAR, missing data, MCD estimator, robustness, rounded zeros