A multivariate Poisson regression model for count data.

We propose a new technique for the study of multivariate count data. The proposed model is applied to the study of the number of individuals several fossil species found in a set of geographical observation points. First, we are proposing a multivariate model based on the Poisson distributions, which allows positive and negative correlations between the components. We are extending the log-linear Poisson model in the multivariate case through the conditional distributions. For this model, we obtain the maximum likelihood estimates and compute several goodness of fit statistics. Finally we illustrate the application of the proposed method over data sets: various simulated data sets and a count data set of various fossil species.

An application of mixture distributions in modelization of length of hospital stay.

Length of hospital stay (LOS) is an important indicator of the hospital activity and management of health care. The skewness exhibited by this variable poses problems in statistical modeling. The aim of this work is to model the variable LOS within diagnosis-related groups (DRG) through finite mixtures of distributions. A mixture of the union of Gamma, Weibull and Lognormal families is used in the model, instead of a mixture of a unique distribution family. Some theoretical questions regarding the model, such as the identifiability and study of asymptotic properties of ML estimators, are analyzed. The EM algorithm is proposed for performing these estimators. Finally, this new proposed model is illustrated by using data from different DRGs.

[Comparative study of two lipid emulsions in the parenteral nutrition of the septic patient]. / Estudio comparativo de dos emulsiones lipídicas en la nutrición parenteral del enfermo séptico.

The nutritional support is essential in the treatment of the septic patient, but the optimal substrates, have not been well defined, although several studies advise the use of solutions with a high proportion of branched amino acids. The use of lipids in the Parenteral Nutrition (PN) of these patients is presently accepted by all authors, although there is no consensus of the composition of the mix to be used. We have done a prospective, randomized study in a group of critical septic patients who received PN. All cases were used a solution with a high proportion of branched amino acids and glucose. 40% of the non-protein calories were administered as lipids. Based on this, two groups were formed. Group 1 medium chain triglycerides and long chain triglycerides (MCT/LCT) in a ratio of 1:1, and Group II LCT. After ten days, both groups showed an increase in hepatic cholestasis enzymes and an improvement of the parameters of protein anabolism and catabolism. Group 1 showed a significantly higher increase in the retinol birdring protein and the improvement of the nitrogen balance. Besides this, the global analysis of all the parameters of protein anabolism and catabolism showed a more favorable evolution, with statistical significance, in those who received MCT/LCT. Therefore, the MCT/LCT in the PN of the septic patient who is given a solution rich in branched amino acids, achieves a greater protein saving and a faster recevesy of the markers of protein synthesis, than those with LCT. Both groups show an increase in cholestasis enzymes.