Aging Intensity for Step-Stress Accelerated Life Testing Experiments.

The aging intensity (AI), defined as the ratio of the instantaneous hazard rate and a baseline hazard rate, is a useful tool for the describing reliability properties of a random variable corresponding to a lifetime. In this work, the concept of AI is introduced in step-stress accelerated life testing (SSALT) experiments, providing new insights to the model and enabling the further clarification of the differences between the two commonly employed cumulative exposure (CE) and tampered failure rate (TFR) models. New AI-based estimators for the parameters of a SSALT model are proposed and compared to the MLEs in terms of examples and a simulation study.

Exact Mediation Analysis for Ordinal Outcome and Binary Mediator.

With reference to a single mediator context, this brief report presents a model-based strategy to estimate counterfactual direct and indirect effects when the response variable is ordinal and the mediator is binary. Postulating a logistic regression model for the mediator and a cumulative logit model for the outcome, we present the exact parametric formulation of the causal effects, thereby extending previous work that only contained approximated results. The identification conditions are equivalent to the ones already established in the literature.

-Divergence in Contingency Table Analysis.

The ϕ -divergence association models for two-way contingency tables is a family of models that includes the association and correlation models as special cases. We present this family of models, discussing its features and demonstrating the role of ϕ -divergence in building this family. The most parsimonious member of this family, the model of ϕ -scaled uniform local association, is considered in detail.

Ordinal probability effect measures for group comparisons in multinomial cumulative link models.

We consider simple ordinal model-based probability effect measures for comparing distributions of two groups, adjusted for explanatory variables. An "ordinal superiority" measure summarizes the probability that an observation from one distribution falls above an independent observation from the other distribution, adjusted for explanatory variables in a model. The measure applies directly to normal linear models and to a normal latent variable model for ordinal response variables.

Murine pheromone proteins constitute a context-dependent combinatorial code governing multiple social behaviors.

During social interactions, an individual's behavior is largely governed by the subset of signals emitted by others. Discrimination of "self" from "other" regulates the territorial urine countermarking behavior of mice. To identify the cues for this social discrimination and understand how they are interpreted, we designed an olfactory-dependent countermarking assay.

GEE for multinomial responses using a local odds ratios parameterization.

In this article, we propose a generalized estimating equations (GEE) approach for correlated ordinal or nominal multinomial responses using a local odds ratios parameterization. Our motivation lies upon observing that: (i) modeling the dependence between correlated multinomial responses via the local odds ratios is meaningful both for ordinal and nominal response scales and (ii) ordinary GEE methods might not ensure the joint existence of the estimates of the marginal regression parameters and of the dependence structure. To avoid (ii), we treat the so-called "working" association vector α as a "nuisance" parameter vector that defines the local odds ratios structure at the marginalized contingency tables after tabulating the responses without a covariate adjustment at each time pair.

The prognostic value of electroencephalography in epilepsy: a long-term follow-up study.

Predicting the evolution of epilepsy is of obvious importance for patients and their families. Value of electroencephalography (EEG) is extensively used in the diagnosis of epilepsy yet its role as a prognostication method remains unclear. The aim of the present retrospective study is to investigate the relationship between serial EEG recordings and long-term clinical and social outcomes in a cohort of patients with epilepsy.

Hospitalization rates for cholelithiasis and acute cholecystitis doubled for the aged population in Greece over the past 30 years.

Objective: Gallbladder disease is becoming increasingly prevalent in Western countries and is a common cause of hospitalization. The objective of this study was to determine time trends in cholelithiasis and acute cholecystitis for hospitalization and disease case fatality in Greece between 1970 and 1998.

Material And Methods: Data were obtained from the Annual Bulletin for the Social Welfare and Health Statistics of the National Statistics Service of Greece.

Valproate-induced eosinophilia in children with epilepsy: role of interleukin-5.

Interleukin-5 contributes both in eosinophilopoiesis and neural development. Serum interleukin-5 levels were measured with enzyme-linked immunosorbent assay technique in 68 children with epilepsy receiving sodium valproate monotherapy and compared with the levels of 60 healthy controls and 14 children with epilepsy receiving carbamazepine. Eosinophilia was observed in 35.