4 research outputs found
Revisiting Relations between Stochastic Ageing and Dependence for Exchangeable Lifetimes with an Extension for the IFRA/DFRA Property
We first review an approach that had been developed in the past years to
introduce concepts of "bivariate ageing" for exchangeable lifetimes and to
analyze mutual relations among stochastic dependence, univariate ageing, and
bivariate ageing. A specific feature of such an approach dwells on the concept
of semi-copula and in the extension, from copulas to semi-copulas, of
properties of stochastic dependence. In this perspective, we aim to discuss
some intricate aspects of conceptual character and to provide the readers with
pertinent remarks from a Bayesian Statistics standpoint. In particular we will
discuss the role of extensions of dependence properties. "Archimedean" models
have an important role in the present framework. In the second part of the
paper, the definitions of Kendall distribution and of Kendall equivalence
classes will be extended to semi-copulas and related properties will be
analyzed. On such a basis, we will consider the notion of "Pseudo-Archimedean"
models and extend to them the analysis of the relations between the ageing
notions of IFRA/DFRA-type and the dependence concepts of PKD/NKD
Multivariate negative aging in an exchangeable model of heterogeneity
We introduce an exchangeable model, which accounts for heterogeneity and dependence at a time. Based on this model, we show how situations of multivariate negative ageing arise in a natural way from conditions of heterogeneity
Diagonal sections of copulas, multivariate conditional hazard rates and distributions of order statistics for minimally stable lifetimes
As a motivating problem, we aim to study some special aspects of the marginal
distributions of the order statistics for exchangeable and (more generally) for
minimally stable non-negative random variables . In any case,
we assume that are identically distributed, with a common
survival function and their survival copula is denoted by .
The diagonal's and subdiagonals' sections of , along with ,
are possible tools to describe the information needed to recover the laws of
order statistics.
When attention is restricted to the absolutely continuous case, such a joint
distribution can be described in terms of the associated multivariate
conditional hazard rate (m.c.h.r.) functions. We then study the distributions
of the order statistics of also in terms of the system of the
m.c.h.r. functions. We compare and, in a sense, we combine the two different
approaches in order to obtain different detailed formulas and to analyze some
probabilistic aspects for the distributions of interest. This study also leads
us to compare the two cases of exchangeable and minimally stable variables both
in terms of copulas and of m.c.h.r. functions. The paper concludes with the
analysis of two remarkable special cases of stochastic dependence, namely
Archimedean copulas and load sharing models. This analysis will allow us to
provide some illustrative examples, and some discussion about peculiar aspects
of our results
Strategie differenziate nelle popolazioni target: I bambini [Strategies for cardiovascular prevention in children]
L’obesità , insieme ad abitudini alimentari
scorrette e comportamenti sedentari, rappresenta
un fattore di rischio per le malattie cardiovascolari.
Per programmare interventi di
prevenzione dell’obesità infantile e valutarne
l’efficacia è necessario disporre di validi sistemi
di sorveglianza. OKkio alla SALUTE si inserisce
in questo contesto con lo scopo di descrivere
la variabilità geografica e l’evoluzione
temporale della stato ponderale dei bambini
delle scuole primarie in Italia, degli stili alimentari,
della pratica dell’attività fisica1.
Con OKkio alla SALUTE, l’Italia partecipa
al progetto europeo European Childhood
Obesity Surveillance Initiative, coordinato dal
WHO Regione Europea, che prevede indagini
epidemiologiche ripetute a cadenza regolare
sui bambini di etĂ 6-9 anni che frequentano la
scuola primaria. Nel contesto italiano, OKkio
alla SALUTE è parte integrante del progetto
“Sistema di indagini sui rischi comportamentali
in età 6-17 anni” promosso e finanziato
nel 2007 dal Centro Nazionale per la Prevenzione
e il Controllo delle Malattie (CCM) del
Ministero della Salute e affidato al coordinamento
del Centro Nazionale di Epidemiologia,
Sorveglianza e Promozione della Salute
(CNESPS) dell’Istituto Superiore di Sanità (ISS)