Handling non-ignorable dropouts in longitudinal data: A conditional model based on a latent Markov heterogeneity structure

We illustrate a class of conditional models for the analysis of longitudinal data suffering attrition in random effects models framework, where the subject-specific random effects are assumed to be discrete and to follow a time-dependent latent process. The latent process accounts for unobserved heterogeneity and correlation between individuals in a dynamic fashion, and for dependence between the observed process and the missing data mechanism. Of particular interest is the case where the missing mechanism is non-ignorable. To deal with the topic we introduce a conditional to dropout model. A shape change in the random effects distribution is considered by directly modeling the effect of the missing data process on the evolution of the latent structure. To estimate the resulting model, we rely on the conditional maximum likelihood approach and for this aim we outline an EM algorithm. The proposal is illustrated via simulations and then applied on a dataset concerning skin cancers. Comparisons with other well-established methods are provided as well

The Optical Approach to Casimir Effects

We propose a new approach to the Casimir effect based on classical ray optics. We define and compute the contribution of classical optical paths to the Casimir force between rigid bodies. Our approach improves upon the proximity force approximation. It can be generalized easily to arbitrary geometries, different boundary conditions, to the computation of Casimir energy densities and to many other situations. This is a brief introduction to the method. Joint work with R.L.Jaffe.Comment: Talk given at the conference `Continuous Advances in QCD 2004', University of Minnesot

V39: an unusual object in the field of IC 1613

The variable star V39 in the field of IC 1613 is discussed in the light of the available photometric and new spectroscopic data. It has strong emission Balmer lines, and the observed characteristics could be explained by a W Vir pulsating star with a period of 14.341 d, located at more than 115 kpc, that is in the very outer halo of our Galaxy. It should have an apparent companion, a long period (1118d) red variable, belonging to IC 1613. The main uncertainty in this interpretation is an emission feature at 668.4 nm, which we tentatively identified as a He I line.Comment: 5 pages; accepted for publication in Astronomy & Astrophysic

FAIRNESS OF NATIONAL HEALTH SERVICE IN ITALY: A BIVARIATE CORRELATED RANDOM EFFECTS MODEL

In this paper we consider a possible way of measuring equity in health as the absence of systematic disparities in health (or in the major social determinants of health) between groups with different levels of underlying social advantage/disadvantage. Starting from the fairness approach developed by the World Health Organization, we propose to extend the analysis of fairness in nancing contribution through a generalized linear mixed models framework by introducing a bivariate correlated random effects model. We aim at analyzing the burden of health care payment on Italian households by modeling catastrophic payments and impoverishment due to health care expenditures. For this purpose, we describe a bivariate model for binary data, where association between the outcomes is modeled through outcome-specic latent effects which are assumed to be correlated; we show how model parameters can be estimated in a nite mixture context. By using such model specication, the fairness of the Italian national health service is investigated.fairness, health care, random eects models, binary data, non parametric maximum likelihood.

The links between international production and innovation: a double network approach

This paper examines the changing role of multinationals in the global generation, adoption and transfer of innovation. It is argued that the combination of traditional asset exploiting objectives with increasing asset seeking activities entails a transition of multinationals towards a double network structure. On the one hand multinationals are more and more characterised by the interconnection of a large number of internal units that are deeply involved in the company’s use, generation and absorption of knowledge. On the other hand, units belonging to the internal network tend to develop external networks with other firms and institutions that are located outside the boundaries of the multinational firm, in order to increase the potential for use, generation and absorption of knowledge. Extending the analysis to a more general level, it is suggested that each of the external actors with which multinationals are interconnected across countries are themselves involved in extensive webs of relationships with other firms and institutions. By becoming embedded in different local contexts, multinational firms act as bridging institutions connecting a number of geographically dispersed economic and innovation systems. As a result, they are conditioned by, and contribute to, the evolution of different contexts in which they operate.innovation, multinational firms, networks.

What Chinese sources really have to say about the dates of the Buddha

This paper suggests that material scattered among the Buddhist sources in Chinese, which has only received very inadequate treatment so far, may warrant a major reassessment of the chronologies of the Buddha's death