A shared-parameter continuous-time hidden Markov and survival model for longitudinal data with informative dropout

A shared-parameter approach for jointly modeling longitudinal and survival data is proposed. With respect to available approaches, it allows for time-varying random effects that affect both the longitudinal and the survival processes. The distribution of these random effects is modeled according to a continuous-time hidden Markov chain so that transitions may occur at any time point. For maximum likelihood estimation, we propose an algorithm based on a discretization of time until censoring in an arbitrary number of time windows. The observed information matrix is used to obtain standard errors. We illustrate the approach by simulation, even with respect to the effect of the number of time windows on the precision of the estimates, and by an application to data about patients suffering from mildly dilated cardiomyopathy

A Maximum Entropy Procedure to Solve Likelihood Equations

In this article, we provide initial findings regarding the problem of solving likelihood equations by means of a maximum entropy (ME) approach. Unlike standard procedures that require equating the score function of the maximum likelihood problem at zero, we propose an alternative strategy where the score is instead used as an external informative constraint to the maximization of the convex Shannon\u2019s entropy function. The problem involves the reparameterization of the score parameters as expected values of discrete probability distributions where probabilities need to be estimated. This leads to a simpler situation where parameters are searched in smaller (hyper) simplex space. We assessed our proposal by means of empirical case studies and a simulation study, the latter involving the most critical case of logistic regression under data separation. The results suggested that the maximum entropy reformulation of the score problem solves the likelihood equation problem. Similarly, when maximum likelihood estimation is difficult, as is the case of logistic regression under separation, the maximum entropy proposal achieved results (numerically) comparable to those obtained by the Firth\u2019s bias-corrected approach. Overall, these first findings reveal that a maximum entropy solution can be considered as an alternative technique to solve the likelihood equation

Exact Multivariate Permutation Tests for Fixed Effects in Mixed-Models

A test for the fixed effect in mixed-models is proposed. It is based on permutation strategy and is exact. The testing approach presented is very general and the class of model covered is very broad. Multivariate responses with different type of variables (e.g. continuous, categorical and ranks) are usually tested with separated models and the overall test are usually reached trough Bonferroni-like combinations, i.e. without taking in account the joint distribution of the tests statistics. On the contrary in this approach the joint distribution is immediately obtained and the dependence among tests is taken in account in the overall test

k-FWER control without multiplicity correction, with application to detection of genetic determinants of multiple sclerosis in Italian twins

We show a novel approach for k-FWER control which does not involve any correction, but only testing the hypotheses along a (possibly datadriven) order until a suitable number of p-values are found above the uncorrected α level. p-values can arise from any linear model in a parametric or non parametric setting. The approach is not only very simple and computationally light, but also the data-driven order enhances power when the sample size is small (and also when k and/or m is large). We illustrate the method on an original study about gene discovery in multiple sclerosis, in which were involved a small number of couples of twins, discordant by disease

El árido calizo como árido para hormigones autocompactantes (HAC)

Siempre que se pretende investigar en el mundo del hormigón no se utiliza el árido calizo para realizar los ensayos, se utilizan áridos silícicos como patrón, y los resultados obtenidos se extrapola a los áridos calizos. Esto se ha demostrado no correcto ya que no es extrapolable los resultados en muchos casos, y este artículo es un ejemplo, y normalmente el comportamiento del árido calizo es más favorable. Los ensayos realizados con árido grueso, árido fino y finos calizos han demostrado unos óptimos resultados para hormigones autocompactantes (HAC). Los finos calizos obtienen un óptimo resultado en la plasticidad y estabilidad del hormigón, con la ayuda del aditivo de policarboxilato y el modulador de viscosidad, se consiguen todas las clases de hormigones autocompactantes para rampas, para muros y hasta para suelos (forjados-soleras), los áridos gruesos obtienen una óptima adherencia con el cemento y los áridos finos rellenan los huecos que no han ocupado los finos. Consiguiéndose resistencias mecánicas hasta los 65 MPa a los 28 días y manteniendo las características de los hormigones autocompactantes. Por tanto se concluye que el árido calizo es un excelente árido para la obtención de hormigones autocompactantes, pero es necesaria una cuidada distribución granulométrica, una adecuada dosificación y un enérgico amasado para conseguir la homogeneidad del hormigón

Patterns of competition and strategic groups in the special cheese industry in Brazil

The aim of this study is to identify the competition pattern in the Brazilian special cheese industry, and the strategic groups of this market. Based mainly on the Industrial Organization Theory, a qualitative study was conducted, supported by primary and secondary data. The primary data were obtained through interviews with six managers of Brazilian special cheese companies, and the secondary data were obtained from websites, company documents and specialized publications. The results point to the increasing importance of the price variable, related to market growth in recent years, which attracted companies with more effective production and logistics structures. Based on the characteristics and strategies of companies, four strategic groups were identified: a) medium sized companies with large market penetration; b) small companies focused on the special cheese market and located in traditional production regions of Minas Gerais State; c) single-product companies, with high levels of vertical integration; and d) transnational companies that produce special cheese in several countries.Fine cheese, industrial organization, strategic groups, Agribusiness, Agricultural Finance, Industrial Organization,

Avaliação da composição da uva e do vinho varietal 'Tempranillo' segundo a época de produção, na região do Vale do Submédio São Francisco.

O Vale do Submédio do São Francisco é a segunda região produtora de vinhos finos do Brasil, sendo responsável por 15% da produção nacional, com oito milhões de litros/ano

Hemisphere Mixing: a Fully Data-Driven Model of QCD Multijet Backgrounds for LHC Searches

A novel method is proposed here to precisely model the multi-dimensional features of QCD multi-jet events in hadron collisions. The method relies on the schematization of high-pT QCD processes as 2->2 reactions made complex by sub-leading effects. The construction of libraries of hemispheres from experimental data and the definition of a suitable nearest-neighbor-based association map allow for the generation of artificial events that reproduce with surprising accuracy the kinematics of the QCD component of original data, while remaining insensitive to small signal contaminations. The method is succinctly described and its performance is tested in the case of the search for the hh->bbbb process at the LHC.Comment: 4 pages plus header, 1 figure, proceedings of EPS 2017 Venic