Faces Attract Infants' Attention in Complex Displays

Infant's face preferences have previously been assessed in displays containing 1 or 2 faces. Here we present 6‐month‐old infants with a complex visual array containing faces among multiple visual objects. Despite the competing objects, infants direct their first saccade toward faces more frequently than expected by chance (Experiment 1). The attention‐grabbing effect of faces is not selective to upright faces (Experiment 2) but does require the presence of internal facial elements, as faces whose interior has been phase‐scrambled did not attract infants' attention (Experiment 3). On the contrary, when the number of fixations is considered, upright faces are scanned more extensively than both inverted and phase‐scrambled faces. The difference in selectivity between the first look measure and the fixation count measure is discussed in light of a distinction between attention‐grabbing and attention‐holding mechanisms.     

Graphical Tests for the Frailty Distribution in the Shared Frailty Model

We extend a diagnostic plot for the frailty distribution in proportional hazards models to the case of shared frailty. The plot is based on a closure property of exponential family failure distributions with canonical statistics z and g(z), namely that the frailty distribution among survivors at time t has the same form, with the same values of the parameters associated with g(z). We extend this property to shared frailty, considering various definitions of a “surviving” cluster at time t. We illustrate the effectiveness of the method in the case where the “death” of the cluster is defined by the first death among its members.     

Join the Union and Be Safe: The Effects of Unionization on Occupational Safety and Health in the European Union

This paper investigates the effect of unionization on occupational safety and health, as measured by the fatal and non‐fatal work accidents, after controlling for the country's gross domestic product. It uses a panel sample of 10 European Union countries, for the period 1982–2006. The study takes into account the time persistence in work injuries and the endogenous nature of the work injuries–union density relationship. In addition, the effect of union density is decomposed into a temporary and permanent effect. It is shown that increasing union density is associated with a decrease in the number of both fatal and non‐fatal work injuries.     

Modelling survival data using mixtures of frailties

Frailty models are often used to describe the extra heterogeneity in survival data by introducing an individual random, unobserved effect. The frailty term is usually assumed to act multiplicatively on a baseline hazard function common to all individuals. In order to apply the frailty model, a specific frailty distribution has to be assumed. If at least one of the latent variables is continuous, the frailty must follow a continuous distribution. In this paper, a finite mixture of continuous frailty distributions is used in order to describe situations in which one (or more) of the latent variables separates the population in study into two (or more) subpopulations. Closure properties of the unobserved quantity are given along with the maximum-likelihood estimates under the most common choices of frailty distributions. The model is illustrated on a set of lifetime data.     

The use of length‐biased distributions in statistical monitoring

Statistical process monitoring (SPM) has been used extensively recently in order to assure the quality of the output of industrial processes. Techniques of SPM have been efficiently applied during the last two decades in non‐industrial processes. A field of application with great interest is public health monitoring, where a pitfall with which we have to deal is the fact that available samples are not random in all cases. In the majority of cases, we monitor measurements derived from patient admissions to a hospital against control limits that were calculated using a sample of data taken from an epidemiological survey. In this work, we bridge the gap of a change in the sampling scheme from Phase I to Phase II, studying the case where the sampling during Phase II is biased. We present the appropriate methodology and then apply extensive numerical simulation in order to explore the performance of the proposed methodology, for measurements following various asymmetrical distributions. As the simulations show, the proposed methodology has a significantly better performance than the standard procedure.     

Sample Tests for Detection of Size-Biased Sampling Mechanism

The aim of this article is to present a new test for the detection of size-bias in a sample with or without censored observations. The test is simple in the form and demands only the knowledge of consistent estimators of any nuisance parameters appeared in the model. With the use of simulated samples from the Weibull distribution, we show the advantages of the new test compared to the Likelihood Ratio and the Wald test.     

On Small Samples Testing for Frailty Through Homogeneity Test

We derive a test in order to examine the need of modeling survival data using frailty models based on the likelihood ratio (LR) test for homogeneity. Test is developed for both complete and censored samples from a family of baseline distributions that satisfy a closure property. Approach motivated by I-divergence distance is used in order to determine “credible” regions for all parameters of baseline distribution for which homogeneity hypothesis is not rejected. Proposed test outperforms the usual asymptotic LR test both in very small samples with known frailty and for all small sample sizes under misspecified frailty.