Understanding power at tax investigation: the portuguese tax inspector’s view

The tax inspection procedure depends on a set of interactions between the tax inspector and the taxpayer. Tax inspectors are responsible for conducting this relationship and they have a large set of legal prerogatives to use - power actions. The way those power actions are used may define the taxpayers propensity to regularize their tax situation or, on the contrary, adopt a position of resistance or confrontation. From a questionnaire carried out with 85 Portuguese Tax Inspectors (PTIs), 40 power actions were analyzed. We identify five different levels of power actions according to their harshness. We have also analyzed the correlations between frequency of use and perceived efficiency. We conclude that PTIs do not use more invasive power actions very often, even though these are perceived as more efficient.publishe

Looking for atypical groups of distributions in the context of genomic data

This work addresses the problem of detecting groups of observations (distributions) and flagging those that differ abnormally from the majority of the groups, termed as atypical groups. The proposed method combines a hierarchical classification technique, to identify groups of similar distributions, with a functional outlier detection method, to identify those groups that contain outliers. Groups with outlying observations are forwarded for sub clustering. Once the final partition is obtained, each cluster is represented by a class prototype, whose outlyingness is evaluated according to a functional approach. Clusters with atypical class labels are flagged as atypical groups. The method is applied for the detection of groups of atypical genomic words, based on their distances distributions.publishe

The influence of the portuguese sovereign debt ratings on treasury bond yeilds performance

The rating agencies are often among those accused of taking part in the sovereign debt instability that followed the financial crisis of 2008. This work intends to empirically analyse the influence of changes in the Portuguese sovereign debt rating, as attributed by the three main international rating agencies (Moody’s, S&P e Fitch), in the performance of mid to long-term treasury bond yields (2, 5 and 10 years) over the period between February 2003 and May 2012. Using simple and multiple linear regression models, estimated through the OLS method, and through the application of Chow’s test, the statistical evidence shows that the changes in sovereign debt rating have a negative and significant impact on the performance of treasury bond yields for all maturities studied and this influence is higher for the period after the sovereign debt crisis. The evidence also show that the impact of changes in sovereign debt rating in treasury bond yields increases with the loss of investment grade.info:eu-repo/semantics/publishedVersio

Identification of clinical phenotypes of patients with Chronic Obstructive Pulmonary Disease (COPD)

Sem resumo disponível.publishe

Clinical characteristics of patients with chronic obstructive pulmonary disease (COPD): are they different

Sem resumo disponível.publishe

Sleep and Academic Performance in Undergraduates: A Multi-measure, Multi-predictor Approach

The present study examined the associations of sleep patterns with multiple measures of academic achievement of undergraduate university students and tested whether sleep variables emerged as significant predictors of subsequent academic performance when other potential predictors, such as class attendance, time devoted to study, and substance use are considered. A sample of 1654 (55% female) full-time undergraduates 17 to 25 yrs of age responded to a self-response questionnaire on sleep, academics, lifestyle, and well-being that was administered at the middle of the semester. In addition to self-reported measures of academic performance, a final grade for each student was collected at the end of the semester. Univariate analyses found that sleep phase, morningness/eveningness preference, sleep deprivation, sleep quality, and sleep irregularity were significantly associated with at least two academic performance measures. Among 15 potential predictors, stepwise multiple regression analysis identified 5 significant predictors of end-of-semester marks: previous academic achievement, class attendance, sufficient sleep, night outings, and sleep quality (R(2)=0.14 and adjusted R(2)=0.14, F(5, 1234)= 40.99, p < .0001). Associations between academic achievement and the remaining sleep variables as well as the academic, well-being, and lifestyle variables lost significance in stepwise regression. Together with class attendance, night outings, and previous academic achievement, self-reported sleep quality and self-reported frequency of sufficient sleep were among the main predictors of academic performance, adding an independent and significant contribution, regardless of academic variables and lifestyles of the students

Aspectos matemáticos da entropia

Com o presente trabalho pretende-se fazer uma abordagem ao desenvolvimento do conceito Entropia. Inicia-se esta dissertação com a apresentação de uma perspectiva histórica da evolução do conceito. Enunciam-se as propriedades mais importantes das entropias de Shannon, Rényi e de Tsallis, assim como do ganho de informação de Kullback-Leibler. Apresentam-se as demonstrações de algumas destas propriedades. São expostas e analisadas as definiçõpes axiomáticas da entropia de Shannon e de Tsallis. Menciona-se ainda a definição axiomática do ganho de informação de Rényi, que conduz à definição da entropia de Rényi. ABSTRACT: This work intends to be an approach of the development of the concept of Entropy. We start with an historical perspective of the evolution of this concept. Several properties of the Shannon, Rényi and Tsallis entropies are presented, likewise Kullback-Leibler’s gain of information. Some of this properties are followed by it’s proof. We present and discuss the axiomatic definition of Shannon and Tsallis entropies. We also refer axiomatic definition of Rényi’s gain of information, which defines Rényi’s entropy

Directional outlyingness applied to distances between genomic words

The detection of outlier curves/images is crucial in many areas, such as environmental, meteorological, medical, or economic contexts. In the functional framework, outlying observations are not only those that contain atypically high or low values, but also curves that present a different shape or pattern from the rest of the curves in the sample. In this short paper, we mention some recent methods for outlier detection in functional data and apply a recently proposed measure, the directional outlyingness, and the functional outlier map to detect words with outlying distance distribution in the human genome.publishe

Análise de distribuições de distâncias entre palavras genómicas

The investigation of DNA has been one of the most developed areas of research in this and in the last century. However, there is a long way to go to fully understand the DNA code. With the increasing of DNA sequenced data, mathematical methods play an important role in addressing the need for e cient quantitative techniques for the detection of regions of interest and overall characteristics in these sequences. A feature of interest in the study of genomic words is their spatial distribution along a DNA sequence, which can be characterized by the distances between words. Counting such distances provides discrete distributions that may be analyzed from a statistical point of view. In this work we explore the distances between genomic words as a mathematical descriptor of DNA sequences. The main goal is to design, develop and apply statistical methods specially designed for their distributions, in order to capture information about the primary and secondary structure of DNA. The characterization of empirical inter-word distance distributions involves the problem of the exponential increasing of the number of distributions as the word length increases, leading to the need of data reduction. Moreover, if the data can be validly clustered, the class labels may provide a meaningful description of similarities and di erences between sets of distributions. Therefore, we explore the inter-word distance distributions potential to obtain a word clustering, able to highlight similar patterns of word distributions as well as summarized characteristics of each set of distributions. With the aim of performing comparative studies between genomic sequences and de ning species signatures, we deduce exact distributions of inter-word distances under random scenarios. Based on these theoretical distributions, we de ne genomic signatures of species able to discriminate between species and to capture their evolutionary relation. We presume that the study of distributions similarities and the clustering procedure allow identifying words whose distance distribution strongly di ers from a reference distribution or from the global behaviour of the majority of the words. One of the key topics of our research focuses on the establishment of procedures that capture distance distributions with atypical behaviours, herein referred to as atypical distributions. In the genomic context, words with an atypical distance distribution may be related with some biological function (motifs). We expect that our results may be used to provide some sort of classi cation of sequences, identifying evolutionary patterns and allowing for the prediction of functional properties, thereby contributing to the advancement of knowledge about DNA sequences.A investigação do ADN é uma das áreas mais desenvolvidas neste e no último século. O crescente aumento do número de genomas sequenciados tem exigido técnicas quantitativas mais e cientes para a identi cação de características gerais e especí cas das sequências genómicas, os métodos matemáticos desempenham um papel importante na resposta a essa necessidade. Uma característica com particular interesse no estudo de palavras genómicas é a sua distribuição espacial ao longo de sequências de ADN, podendo esta ser caracterizada pelas distâncias entre palavras. A contagem dessas distâncias fornece distribuições discretas passíveis de análise estatística. Neste trabalho, exploramos as distâncias entre palavras como um descritor matemático das sequências de ADN, tendo como objetivo delinear e desenvolver procedimentos estatísticos especialmente concebidos para o estudo das suas distribuições. A caracterização das distribuições de distâncias empíricas entre palavras genómicas envolve o problema do crescimento exponencial do número de distribuições com o aumento do comprimento da palavra, gerando a necessidade de redução dos dados. Além disso, se os dados puderem ser validamente agrupados em classes então os representantes de classe fornecem informação relevante sobre semelhanças e diferenças entre cada grupo de distribuições. Assim, exploramos o potencial das distribuições de distâncias na obtenção de um agrupamento de palavras, que agrupe padrões de distâncias semelhantes e que coloque em evidência as características de cada grupo. Com vista ao estudo comparativo de sequências genómicas e à de nição de assinaturas de espécies, focamo-nos no desenvolvimento de modelos teóricos que descrevam distribuições de distâncias entre palavras em cenários aleatórios. Esses modelos são utilizados na de nição de assinaturas genómicas, capazes de discriminar entre espécies e de recuperar relações evolutivas entre estas. Presumimos que o estudo de semelhanças e a análise de agrupamento das distribuições permite identi car palavras cuja distribuição se afasta fortemente de uma distribuição de referência ou do comportamento global das maioria das palavras. Um dos principais tópicos de investigação foca-se na deteção de distribuições com comportamentos anormais, aqui referidas como distribuições atípicas. No contexto genómico, palavras com distribuições de distâncias atípicas poderão estar relacionadas com alguma função biológica (motivos). Esperamos que os resultados obtidos possam ser utilizados para fornecer algum tipo de classi cação de sequências, identi cando padrões evolutivos e permitindo a previsão das propriedades funcionais, representando assim um passo adicional na criação de conhecimento sobre sequências de ADN.Programa Doutoral em Matemátic