Elliptically Symmetric Distributions: A Review of Achieved Results and Open Issues

The spherically and elliptically symmetrical distributions are used in different statistical areas for different purposes such as the description of multivariate data, in order to find alternatives to the normal distribution in multinormality tests and in the creation of statistical models in which the usual assumption of normality is not realistic. Some achieved results, open issues and some proposals for their use in applications, especially in the financial area, are here presented.

A new method to "clean up" ultra high-frequency data

In the applied econometrics, the availability of ultra high-frequency databases is having an important impact on the research market microstructure theory. The ultra high-frequency databases contain detailed reports of all the financial market activity information which is available. However, ultra high-frequency databases cannot be directly used. On one hand recording mistakes can be present, on the other hand missing information has to be inferred from the available data. In this paper, we propose a simple method in order to clean up the ultra high-frequency data from possible errors and we examine the method efficacy when we analyze data by using an autoregressive conditional duration (A…

Different methods to clean up ultra high frequency data

gastric polypoid lesions. Our ecperience.

BACKGROUND AND AIM: The Authors report the results of their experience on polypoids lesions of the stomach and on endoscopic polypectomies. PATIENTS AND METHODS: A study on 2000 OGD (oesophagogastroduodenoscopy) has been carried out on 95 patients with polypoid lesions. The authors have analysed the associations existing between histological type and symptomatology and localisation of the lesion and the status of the Helicobacter pylori and the risk of cancerization. The data were confronted with the ones already available. RESULTS: In the majority of the cases, the polypoid lesions were asymptomatic, the localization changed according to the histological type, with the antrum as the most a…

Random effects elliptically distributed in unbalanced linear models

In linear mixed effects models, random effects are used for modelling the variance-covariance structure of the response variable. These models are based on the assumption that the random effects are normally distributed, but in literature alternative random effect distributions have been proposed and the consequences of misspecification are investigated. These studies consider only balanced designs. Aim of this paper is to study an unbalanced linear mixed model with random effects elliptically distributed.