Strategic Project - UI 6 - 2011-2012

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Publications

The impact of winter cold weather on acute myocardial infarctions in Portugal

Publication . Vasconcelos, João; Freire, Elisabete; Almendra, Ricardo; Silva, Giovani L.; Santana, Paula

Mortality due to cardiovascular diseases shows a seasonal trend that can be associated with cold weather. Portugal is the European country with the highest excess winter mortality, but nevertheless, the relationship between cold weather and health is yet to be assessed. The main aim of this study is to identify the contribution of cold weather to cardiovascular diseases within Portugal. Poisson regression analysis based on generalized additive models was applied to estimate the influence of a human-biometeorological index (PET) on daily hospitalizations for myocardial infarction. The main results revealed a negative effect of cold weather on acute myocardial infarctions in Portugal. For every degree fall in PET during winter, there was an increase of up to 2.2% (95% CI ¼ 0.9%; 3.3%) in daily hospital admissions. This paper shows the need for public policies that will help minimize or, indeed, prevent exposure to cold.

2013Journal article

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Known Mean, Unknown Maxima? Testing the Maximum Knowing Only the Mean

Publication . Santos, Rui; Oliveira Martins, João Paulo; Felgueiras, Miguel

In the quantitative group testing problem, the use of the group mean to identify if the group maximum is greater than a prefixed threshold (infected group) is analyzed, using n independent and identically distributed individuals. Under these conditions, it is shown that the information of the mean is sufficient to classify each group as infected or healthy with low probability of misclassification when the underline distribution is a unilateral heavy-tailed distribution.

2015-07Journal article

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Testing the Maximum by the Mean in Quantitative Group Tests

Publication . Martins, João Paulo; Santos, Rui; Sousa, Ricardo

Group testing, introduced by Dorfman in 1943, increases the efficiency of screening individuals for low prevalence diseases. A wider use of this kind of methodology is restricted by the loss of sensitivity inherent to the mixture of samples. Moreover, as this methodology attains greater cost reduction in the cases of lower prevalence (and, consequently, a higher optimal batch size), the phenomenon of rarefaction is crucial to understand that sensitivity reduction. Suppose, with no loss of generality, that an experimental individual test consists in determining if the amount of substance overpasses some prefixed threshold l. For a pooled sample of size n, the amount of substance of interest is represented by (Y1, … , Yn), with mean (Formula Presented) and maximum Mn. The goal is to know if any of the individual samples exceeds the threshold l, that is, Mn > l. It is shown that the dependence between (Formula Presented) and Mn has a crucial role in deciding the use of group testing since a higher dependence corresponds to more information about Mn given by the observed value of (Formula Presented).

2014Book part

Open access

Explaining the seismic moment of large earthquakes by heavy and extremely heavy tailed models

Publication . Felgueiras, Miguel Martins

The search of physical laws that explain the energy released by the great magnitude earthquakes is a relevant question, since as a rule they cause heavy losses. Several statistical distributions have been considered in this process, namely heavy tailed laws, like the Pareto distribution with shape parameter α ≈ 0. 6667. Yet, for the usually considered Californian region (where earthquakes with moment magnitude, MW, greater than 7. 9 were never registered) the Pareto distribution with index near the above mentioned seems to have a "too heavy" tail for explaining the bigger earthquakes seismic moments. Usually an exponential tapper is applied to the distribution right tail (above the so called corner seismic moment), or another distribution is considered to explain these high seismic moment data (like another Pareto with different shape parameter). The situation is different for other regions where seisms of larger magnitudes do occur, leading to data sets for which heavy or even extremely heavy tailed models are appropriated. The purpose of this paper is to reduce the seismic moment, M0, of the very large earthquakes to particular heavy and extremely heavy tailed distributions. Using world seismic moment information, we apply Pareto, Log-Pareto and extended slash Pareto distributions to the data, truncated for M0 ≥ 1021 Nm and for M0 ≥ 1021. 25 Nm. For these great seisms we conclude that extended slash Pareto is a promising alternative to the more traditional Pareto and Log-Pareto distributions as a candidate to the real model underlying the data.

2012-08-15Journal article

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