Modeling the presence of immunes by using the exponentiated-Weibull model

In this paper the exponentiated-Weibull model is modified to model the possibility that long-term survivors are present in the data. The modification leads to an exponentiated-Weibull mixture model which encompasses as special cases the exponential and Weibull mixture models typically used to model such data. Inference for the model parameters is considered via maximum likelihood and also via Bayesian inference by using Markov chain Monte Carlo simulation. Model comparison is considered by using likelihood ratio statistics and also the pseudo Bayes factor, which can be computed by using the generated samples. An example of a data set is considered for which the exponentiated-Weibull mixture model presents a better fit than the Weibull mixture model. Results of simulation studies are also reported, which show that the likelihood ratio statistics seems to be somewhat deficient for small and moderate sample sizes.     

Using Balanced Scorecard (BSC) approach to improve ergonomics programs

The purpose of this paper is to propose foundations for a theory of using the Balanced Scorecard (BSC) methodology to improve the strategic view of ergonomics inside the organizations. This approach may help to promote a better understanding of investing on an ergonomic program to obtain good results in quality and production, as well as health maintenance. It is explained the basics of balanced scorecard, and how ergonomists could use this to work with strategic enterprises demand. Implications of this viewpoint for the development of a new methodology for ergonomics strategy views are offered.     

Using Quality of Life Criteria to Define Urban Areas in Catalonia

The purpose of this paper is to develop the concept and definition of multidimensional urban areas, thereby providing insights into our understanding of the sub-regional structures of household spatial systems. Hence, we propose a framework for strategic planning that considers several areas of household needs. In order to achieve this goal, we develop a multicriteria methodology to define the territorialisation of the region of Catalonia (Spain). We first analyse the different methodologies used to define territorial areas based on economic criteria, for example, those used to construct travel-to-work areas (TTWA), among other methods. Thus, in practice several criteria and techniques are used to organize a territory, including administrative areas, commuting-based algorithms, and gravitational techniques. Finally, these points help us build a system of multicriteria urban areas that is consistent with the overall use of time by individuals.

The Institutional vs. the Academic Definition of the Quality of Work Life. What is the Focus of the European Commission?

In recent years, we have seen how the quality of work life has been focused and defined by the European Commission (EC). In our study we compare the EC definition with the academic one and try to see how close they are. We also analyse the possibility of applying the institutional definition to the Spanish case through the development of specific indicators. Our main conclusions are that QWL is increasingly important for policy makers. In addition, it is essential to have objective indicators and to conduct surveys in order to reliably measure QWL.     

Zero-spiked regression models generated by gamma random variables with application in the resin oil production

Zero-inflated data are more frequent when the data represent counts. However, there are practical situations in which continuous data contain an excess of zeros. In these cases, the zero-inflated Poisson, binomial or negative binomial models are not suitable. In order to reduce this gap, we propose the zero-spiked gamma-Weibull (ZSGW) model by mixing a distribution which is degenerate at zero with the gamma-Weibull distribution, which has positive support. The model attempts to estimate simultaneously the effects of explanatory variables on the response variable and the zero-spiked. We consider a frequentist analysis and a non-parametric bootstrap for estimating the parameters of the ZSGW regression model. We derive the appropriate matrices for assessing local influence on the model parameters. We illustrate the performance of the proposed regression model by means of a real data set (copaiba oil resin production) from a study carried out at the Department of Forest Science of the Luiz de Queiroz School of Agriculture, University of São Paulo. Based on the ZSGW regression model, we determine the explanatory variables that can influence the excess of zeros of the resin oil production and identify influential observations. We also prove empirically that the proposed regression model can be superior to the zero-adjusted inverse Gaussian regression model to fit zero-inflated positive continuous data.     

Cessation of breastfeeding in association with oxytocin administration and type of birth. A prospective cohort study

Background

Some studies have suggested an association between synthetic oxytocin administration and type of birth with the initiation and consolidation of breastfeeding.

Back to the Future: a Sensitivity Analysis to Predict Future Fertility Rates Considering the Influence of Family Policies—The Cases of Spain and Norway

This article analyzes the relationship between family policies focused on childcare for children under the age of three and fertility levels. In the current context of very low European fertility, it is important to understand whether public support for families can help increase fertility or if, on the contrary, existing fertility levels are the exact reflection of the reproductive desires of families, regardless of the family-support of the policies that may exist in each country. This analysis was carried out through a stochastic dynamic mathematical model that incorporates both demographic variables and family policy variables. A sensitivity analysis was carried out on Spain and Norway, two countries that have very different models of family policies. This sensitivity analysis allows establishing a relationship between the existing family policies and the total fertility rate and also the expected evolution of fertility rates in the future, if the current family policies remain constant. The results showed that the models which lead to an increase in fertility are those which are most generous and which also incorporate a gender perspective, so they allow the identification of good practices and maximum levels of policy efficiency in regards to different objectives such as increase fertility and advances towards gender equality. By contrast, models with erratic and insufficient support clearly contribute to maintaining fertility at very low levels and perpetuate unequal gender relationships. There is, therefore, space for state agency to develop more effective public policies in both dimensions.

     

Confidence Intervals on Regression Models with Censored Data

Stute (1993, Consistent estimation under random censorship when covariables are present. Journal of Multivariate Analysis 45, 89–103) proposed a new method to estimate regression models with a censored response variable using least squares and showed the consistency and asymptotic normality for his estimator. This article proposes a new bootstrap-based methodology that improves the performance of the asymptotic interval estimation for the small sample size case. Therefore, we compare the behavior of Stute's asymptotic confidence interval with that of several confidence intervals that are based on resampling bootstrap techniques. In order to build these confidence intervals, we propose a new bootstrap resampling method that has been adapted for the case of censored regression models. We use simulations to study the improvement the performance of the proposed bootstrap-based confidence intervals show when compared to the asymptotic proposal. Simulation results indicate that, for the new proposals, coverage percentages are closer to the nominal values and, in addition, intervals are narrower.     

Testing hypotheses in truncated samples by means of divergence statistics

In this paper we consider the problem of testing hypotheses in parametric models, when only the first r (of n) ordered observations are known.Using divergence measures, a procedure to test statistical hypotheses is proposed, Replacing the parameters by suitable estimators in the expresion of the divergence measure, the test statistics are obtained.Asymptotic distributions for these statistics are given in several cases when maximum likelihood estimators for truncated samples are considered.Applications of these results in testing statistical hypotheses, on the basis of truncated data, are presented.The small sample behavior of the proposed test statistics is analyzed in particular cases.A comparative study of power values is carried out by computer simulation.     

The geometric exponential Poisson distribution

Many if not most lifetime distributions are motivated only by mathematical interest. Here, a new three-parameter distribution motivated mainly by lifetime issues is introduced. Some properties of the new distribution including estimation procedures, univariate generalizations and bivariate generalizations are derived. Two real data applications are described to show superior performance versus some known lifetime models.