Conference Room: Library of Department of Mathematics and Applications (Room EC0.31) - Azurém (Guimarães)
10:00-11:15 |
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Bent Jørgensen
In 1961 L. R. Taylor proposed a power law for the relationship between the spatial mean and variance of population
abundance in ecology, which over time has been observed for a
large number of species, as well as in many other physical, biological, and socio-economic systems.
Many disparate explanations for the power law have been proposed in the literature, but no consensus on
their adequacy has emerged. We review the historical background for the power law and some of the
controversies surrounding it. We then turn to a possible theoretical explanation based on the power
variance functions of the so-called Tweedie distributions. We propose a new spatial self-similarity
hypothesis corresponding to a class of spatial processes with long-range dependence, which in turn
implies a double power law for the spatial variance, one power involving population density, and the
other involving the size of the sampled area. We propose a log-linear spatial regression framework,
which allows simultaneous estimation of the regression and power parameters by means of estimating functions.
Bent Jørgensen
Professor, Department of Mathematics and Computer Science
Professor of Mathematical Statistics, University of Southern Denmark
Department of Mathematics and Computer Science
University of Southern Denmark
Odense M
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11:45-12:30 |
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Helena Mouriño
In December 1995, Sintra was included on the World Heritage List under the name "The Cultural Landscape of Sintra". This classification is related with the pioneering role played by Sintra in the 19th century in establishing the European Romantic architecture.
The UNESCO World Heritage Site designation has substantially increased visitors flow to Sintra. One of the main challenges that local policy-makers are faced with is how to effectively deal with the main impacts of the Sintra's World Heritage status, especially in what concerns to mass tourism. Hence, it becomes crucial to fully understand tourists' satisfaction with this Heritage Site.
To this purpose, in August and September 2010 a survey was conducted to the tourists who visited the Palaces and Parks of Sintra. In this talk, we analyse the main results of the tourist's survey. Different perspectives are discussed: reasons for visiting Sintra and length of stay; transportation to and around Sintra; evaluation of Sintra's World Heritage; characterization of the respondents. An ordinal regression model to describe tourist's satisfaction is proposed.
Helena Mouriño
Department of Statistics and OR - University of Lisbon
Note:This is a joint work with Hugo Roque and Mariana Henriques (FCUL-UL).
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14:00-14:45 |
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Cláudia Neves
The climate change dispute is about changes over time of environmental characteristics (such as rainfall).
Some people say that a possible change is not so much in the mean but rather in the extreme phenomena
(that is, the average rainfall may not change much but heavy storms may become more or less frequent).
The paper studies changes over time in the probability that some high threshold is exceeded.
The model is such that the threshold does not need to be specified, the results hold for any high threshold.
For simplicity a certain linear trend is studied depending on one real parameter. Estimation and testing procedures
(is there a trend?) are developed. Simulation results are presented. The method is applied to trends in heavy rainfall
at 18 gauging stations across Germany and The Netherlands. A tentative conclusion is that the trend seems to depend on
whether or not a station is close to the sea.
Cláudia Neves
Department of Mathematics - University of Aveiro
Note:This is a joint work with Albert Klein Tank and Laurens de Haan.
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14:45-15:30 |
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Juan Carlos Pardo-Fernández
In medical studies the diagnostic of a patient is very often based on some characteristic of interest, which may
lead to classification errors. These classification errors are calibrated on the basis of two indicators:
sensitivity (probability of diagnosing an ill person as ill) and specificity (probability of diagnosing a healthy person
as healthy).
When the diagnostic variable is continuous, the classification will necessarily be based on a cut-off value:
if the variable exceeds the cut-off then the patient is classified as ill, otherwise the patient is classified
as healthy. In this situation, it is of special interest the geometrical locus obtained when varying the
cut-off values in the complement of the specificity versus the sensitivity. This geometrical locus is called the
receiver operating characteristic curve (ROC curve), and it is of extensive use to analyse the discriminative power
of the diagnostic variable. Some summary indicators, such as the area under the curve or Youden's index, are used to
describe the main features of the ROC curve. The first part of the talk will be devoted to give a general
introduction about ROC curves and present some nonparametric estimators.
In many studies, a covariate is avaliable along with the diagnostic variable. The information contained in the
covariate may modify the discriminatory capability of the ROC curve, and therefore it is interesting to study the
impact of the covariate on the conditional ROC curve. The second part of the talk will be devoted to the study
of a nonparametric estimation procedure of the conditional ROC curve and its associated summary indices
(conditional AUC and conditional Youden index). A data set concerning diagnosis of diabetes will be used as an
illustration of the proposed methodology.
Juan Carlos Pardo-Fernández
Department of Statistics and OR - University of Vigo
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15:30-16:15 |
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Rita Gaio
Multivariate finite mixture models have been applied to the identification of dietary patterns. These models are known to have many parameters and consequently large samples are usually required. We present a special case of a multivariate mixture model that reduces the number of parameters to be estimated and seems adequate for small to moderately sized samples. We illustrate our approach with an analysis of Portuguese data from a food-frequency questionnaire, and with a simulation study.
Rita Gaio
Department of Mathematics - University of Porto
Note:
This is a joint work with Joaquim Costa (FCUP-UP) and a team of epidemiologists from ISPUP.
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