Incidence rate and spatio-temporal clustering of type 1 diabetes in Santiago, Chile, from 1997 to 1998

OBJECTIVE: To estimate the incidence rate of type 1 diabetes in the urban area of Santiago, Chile, from March 21, 1997 to March 20, 1998, and to assess the spatio-temporal clustering of cases during that period. METHODS: All sixty-one incident cases were located temporally (day of diagnosis) and spatially (place of residence) in the area of study. Knox's method was used to assess spatio-temporal clustering of incident cases. RESULTS: The overall incidence rate of type 1 diabetes was 4.11 cases per 100,000 children aged less than 15 years per year (95% confidence interval: 3.06--5.14). The incidence rate seems to have increased since the last estimate of the incidence calculated for the years 1986--1992 in the metropolitan region of Santiago. Different combinations of space-time intervals have been evaluated to assess spatio-temporal clustering. The smallest p-value was found for the combination of critical distances of 750 meters and 60 days (uncorrected p-value = 0.048). CONCLUSIONS: Although these are preliminary results regarding space-time clustering in Santiago, exploratory analysis of the data method would suggest a possible aggregation of incident cases in space-time coordinates.

Método de Bootstrap e teoria da credibilidade na estimativa das provisões para sinistros

Dissertação para obtenção do Grau de Mestre em Matemática e Aplicações, no ramo Actuariado, Estatística e Investigação Operacional

Dealing with frame imperfections in a business survey: an empirical study using without replacement bootstrap

This paper approaches issues related to frame problems and nonresponse in surveys. These nonsampling errors affect the accuracy of the estimates whereas the estimators became biased and less precise. We analyse some estimation methods that deal with those problems and give an especial focus to post-stratification procedures.

Validação da Versão Portuguesa da "Activities-specific Balance Confidence Scale"

Introdução: Muitos dos instrumentos disponíveis para a avaliação do equilíbrio, risco de queda e medo de cair medem apenas actividades simples no domicílio e apresentam tendência para um “efeito de tecto” em idosos residentes na comunidade. A “Activities-specific Balance Confidence (ABC) Scale” foi concebida para avaliar o equilíbrio de forma abrangente, num conjunto de actividades de vida diária associadas a um largo espectro de dificuldade. Objectivos: Traduzir para português e adaptar culturalmente para Portugal a “Activities-specific Balance Confidence (ABS) Scale” e avaliar a sua fiabilidade. População e Métodos: Tradução e adaptação cultural do instrumento e subsequente aplicação a uma população idosa portuguesa, para determinação da sua fiabilidade inter-observador, fiabilidade intra-observador e consistência interna. Resultados: Os resultados foram muito homogéneos na grande maioria das comparações realizadas, quer intra-observador, quer inter-observador. A avaliação da consistência interna revelou valores muito elevados. Estes níveis de fiabilidade mantiveram-se mesmo removendo qualquer uma das 16 questões que compõem o questionário, mantendo-se praticamente constantes os valores registados com o questionário completo. Conclusões: A versão portuguesa da escala ABC demonstrou boa fiabilidade intra-observador, fiabilidade inter-observador e consistência interna na avaliação da auto-percepção do equilíbrio para diversas actividades de vida diária numa população idosa portuguesa. Outros trabalhos serão necessários para avaliar a utilidade desta escala na avaliação do risco de queda e do efeito de intervenções terapêuticas nesta população.

Bootstrap performance profiles in stochastic algorithms assessment

Optimization with stochastic algorithms has become a relevant research field. Due to its stochastic nature, its assessment is not straightforward and involves integrating accuracy and precision. Performance profiles for the mean do not show the trade-off between accuracy and precision, and parametric stochastic profiles require strong distributional assumptions and are limited to the mean performance for a large number of runs. In this work, bootstrap performance profiles are used to compare stochastic algorithms for different statistics. This technique allows the estimation of the sampling distribution of almost any statistic even with small samples. Multiple comparison profiles are presented for more than two algorithms. The advantages and drawbacks of each assessment methodology are discussed.

A metodologia Bootstrap associada ao método de Holt-Winters na previsão de séries temporais

Os métodos de alisamento exponencial são muito utilizados na modelação e previsão de séries temporais, devido à sua versatilidade e opção de modelos que integram. Na estatística computacional, a metodologia Bootstrap é muito aplicada em inferência estatística no âmbito de séries temporais. Este estudo teve como principal objectivo analisar o desempenho do método de Holt-Winters associado à metodologia Bootstrap, como um processo alternativo na modelação e previsão de séries temporais.

Effect of oscillatory breathing on the variability of the RR Intervals and its prognostic importance in individuals with left ventricular global systolic dysfunction

OBJECTIVE: To assess the effect of the oscillatory breathing on the variability of RR intervals (VRR) and on prognostic significance after one year follow-up in subjects with left ventricular global systolic dysfunction. METHODS: We studied 76 subjects, whose age ranged from 40 to 80 years, paired for age and gender, divided into two groups: group I - 34 healthy subjects; group II - 42 subjects with left ventricular global systolic dysfunction (ejection fraction < 0.40). The ECG signals were acquired during 600s in supine position, and analyzed the variation of the thoracic amplitude and the VRR. Clinical and V-RR variables were applied into a logistic multivariate model to foretell survival after one year follow-up. RESULTS: Oscillatory breathing was detected in 35.7% of subjects in vigil state of group II, with a concentration of the spectral power in the very low frequency band, and was independent of the presence of diabetes, functional class, ejection fraction, cause of ventricular dysfunction and survival after one year follow-up. In the logistic regression model, ejection fraction was the only independent variable to predict survival. CONCLUSION: 1) Oscillatory breathing pattern is frequent during wakefulness in the left ventricular global systolic dysfunction and concentrates spectral power in the very low band of V-RR; 2) it does not relate to severity and cause of left ventricular dysfunction; 3) ejection fraction is the only independent predictive variable for survival in this group of subjects.

La incidència de l’afinació en el reconeixement auditiu dels intervals harmònics: una experiència a l’inici dels estudis musicals especialitzats de grau mitjà.

L’article presenta una investigació sobre la incidència de l’afinació vocal en el reconeixement auditiu dels intervals harmònics. La recerca s’ha realitzat durant el curs acadèmic 2006-07 en el context del Conservatori Professional de Música de Girona, concretant-se la mostra d’estudi en els alumnes de primer curs de grau mitjà. S’hi exposen en primer lloc les línies bàsiques del concepte d’educació de l’oïda musical, que seguidament s’especifiquen en l’afinació i el reconeixement auditiu dels intervals musicals. Posteriorment es relata el procediment metodològic que s’ha dut a terme en aquest estudi de cas, detallant-se els resultats musicals obtinguts a través de la realització d’un test de nivell de reconeixement auditiu harmònic. Aquest test s’ha efectuat prèviament i posterior a un breu treball d’intervenció vocal. L’estratègia de recerca es completa mitjançant unes enquestes adreçades als alumnes i als seus corresponents professors especialitzats en Llenguatge Musical. Les conclusions de la investigació ens permeten confirmar que l’afinació vocal ha incidit positivament en el reconeixement auditiu dels intervals harmònics.

Catalan's intervals and realizers of triangulations

The Stanley lattice, Tamari lattice and Kreweras lattice are three remarkable orders defined on the set of Catalan objects of a given size. These lattices are ordered by inclusion: the Stanley lattice is an extension of the Tamari lattice which is an extension of the Kreweras lattice. The Stanley order can be defined on the set of Dyck paths of size n as the relation of being above. Hence, intervals in the Stanley lattice are pairs of non-crossing Dyck paths. In a former article, the second author defined a bijection Φ between pairs of non-crossing Dyck paths and the realizers of triangulations (or Schnyder woods). We give a simpler description of the bijection Φ. Then, we study the restriction of Φ to Tamari’s and Kreweras’ intervals. We prove that Φ induces a bijection between Tamari intervals and minimal realizers. This gives a bijection between Tamari intervals and triangulations. We also prove that Φ induces a bijection between Kreweras intervals and the (unique) realizers of stack triangulations. Thus, Φ induces a bijection between Kreweras intervals and stacktriangulations which are known to be in bijection with ternary trees.

A Bootstrap Neural Network Based Heterogeneous Panel Unit Root Test: Application to Exchange Rates

This paper proposes a bootstrap artificial neural network based panel unit root test in a dynamic heterogeneous panel context. An application to a panel of bilateral real exchange rate series with the US Dollar from the 20 major OECD countries is provided to investigate the Purchase Power Parity (PPP). The combination of neural network and bootstrapping significantly changes the findings of the economic study in favour of PPP.

Confidence and Competence in Communication

This paper studies information transmission between an uninformed decision maker (receiver) and an informed player (sender) who have asymmetric beliefs ("con fidence") on the sender s ability ("competence") to observe the state of nature. We fi nd that even when the material payoffs of are perfectly aligned, the sender s over- and underconfi dence on his information give rise to information loss in communication, although they do not by themselves completely eliminate information transmission in equilibrium. However, an underconfi dent sender may prefer no communication to informative communication. We also show that when the sender is biased, overconfi dence can lead to more information transmission and welfare improvement.

A Consistent Nonparametric Bootstrap Test of Exogeneity

This paper proposes a novel way of testing exogeneity of an explanatory variable without any parametric assumptions in the presence of a "conditional" instrumental variable. A testable implication is derived that if an explanatory variable is endogenous, the conditional distribution of the outcome given the endogenous variable is not independent of its instrumental variable(s). The test rejects the null hypothesis with probability one if the explanatory variable is endogenous and it detects alternatives converging to the null at a rate n..1=2:We propose a consistent nonparametric bootstrap test to implement this testable implication. We show that the proposed bootstrap test can be asymptotically justi.ed in the sense that it produces asymptotically correct size under the null of exogeneity, and it has unit power asymptotically. Our nonparametric test can be applied to the cases in which the outcome is generated by an additively non-separable structural relation or in which the outcome is discrete, which has not been studied in the literature.

Self-Confidence, Overconfidence and Prenatal Testosterone Exposure: Evidence from the Lab

This paper examines whether the degree of confidence and overconfidence in one's ability is determined biologically. In articular, we study whether foetal testosterone exposure correlates with an incentive-compatible measure of confidence within an experimental setting. We find that men (rather than women) who were exposed to high testosterone levels in their mother's womb are less likely to overestimate their actual performance, which in turn helps them to gain higher monetary rewards. Men exposed to low prenatal testosterone levels, instead, set unrealistically high expectations which results in self-defeating behaviour. These results from the lab are able to reconcile hitherto disconnected evidence from the field, by providing a link between traders'overconfidence bias, long-term financial returns and prenatal testosterone exposure.