Bayesian assessment of goodness of fit against nonparametric alternatives

The classical chi‐square test of goodness of fit compares the hypothesis that data arise from some parametric family of distributions, against the nonparametric alternative that they arise from some other distribution. However, the chi‐square test requires continuous data to be grouped into arbitrary categories. Furthermore, as the test is based upon an approximation, it can only be used if there are sufficient data. In practice, these requirements are often wasteful of information and overly restrictive. The authors explore the use of the fractional Bayes factor to obtain a Bayesian alternative to the chi‐square test when no specific prior information is available. They consider the extent to which their methodology can handle small data sets and continuous data without arbitrary grouping.     

Cohabitation, Marriage, and First Birth: The Interrelationship of Family Formation Events in Spain

In this paper, we investigate (1) the mutualcausal relationship between first unionformation and first childbirth, and (2) theexistence of constant unmeasured determinantsshared by these two events. We argue that thesedeterminants mainly consist of valueorientations that are heterogeneous in thepopulation. We apply event-history techniquesto retrospective survey data on Spain, allowingfor unobserved heterogeneity components whichsimultaneously affect the two processes. Ourfindings confirm the existence of a strongselection effect, which influences both unionformation and first birth. When controlling forthese shared factors, we find that the risk ofconception increases immediately at marriage,and it continues to be high during thefollowing four years. Entry into cohabitation,in contrast, produces a much smaller increasein the relative risk of conception. The effectof conception on union formation isparticularly strong during pregnancy, but itdeclines sharply after delivery.     

The Influence of Stakeholders on the Environmental Strategy of Service Firms: The Moderating Effects of Complexity,Uncertainty and Munificence*

Drawing on the resource‐based view of the firm, we examine how complexity, uncertainty and munificence in the general business environment moderate the association between a firm's stakeholder integration capability and its environmental strategy. Our data were drawn from 134 ski resorts in 12 countries in western Europe and North America. Our study finds that (1) an organizational capability of stakeholder integration is associated with a service firm's adoption of a proactive environmental strategy; (2) an uncertain business environment has a direct positive influence and a complex business environment has a direct negative influence on a firm's environmental strategy; and (3) complexity has a negative moderating influence on the relationship between a firm's stakeholder integration capability and its environmental strategy.     

Experimentation order in factorial designs with 8 or 16 runs

Randomizing the order of experimentation in a factorial design does not always achieve the desired effect of neutralizing the influence of unknown factors. In fact, with some very reasonable assumptions, an important proportion of random orders afford the same degree of protection as that obtained by experimenting in the design matrix standard order. In addition, randomization can induce a big number of changes in factor levels and thus make experimentation expensive and difficult. This paper discusses this subject and suggests experimentation orders for designs with 8 or 16 runs that combine an excellent level of protection against the influence of unknown factors, with the minimum number of changes in factor levels.     

Monk business: An example of the dynamics of organizations

In this paper we present a dynamic model of an organization. It is shown that the quality of the members of the organization may change cyclically and that even if the organization promotes excellence, the organization may end up populated mostly by mediocre agents.I am grateful to Carmen Beviá, Clara Eugenia García, Iñigo Iturbe-Ormaetxe, Ignacio Ortuño-Ortín, Piero Gottardi, an anonymous referee and the participants in a seminar in the Institute for Advanced Studies, Vienna for very helpful comments and to CICYT for financial support under grant BEC2002-02194.     

Psychophysiological stress reactions, trapezius muscle activity, and neck and shoulder pain among female cashiers before and after introduction of job rotation

The aim of this study was to evaluate the effects of the introduction of a job rotation model on supermarket cashiers, with respect to psychophysiological stress reactions, muscle activity of the trapezius muscle (which covers the upper back, the neck and the shoulder), and musculoskeletal symptoms in the neck and shoulders. Thirty-one female cashiers were investigated before and after job rotation was introduced. Before the reorganization the participants were only performing cash register work at the checkout counters. After the reorganization they shifted between cash register work and work in different departments in the supermarket. At follow-up the participants, all right-handed, had a significantly lower diastolic blood pressure, and surface electromyography (EMG) showed a significantly decreased muscle activity in the trapezius muscle on the left side. Musculoskeletal symptoms of the neck and shoulders were only partly changed, and there was no change in prevalence of musculoskeletal pain, which was around 70%. From questionnaires, but not from self-ratings during work, it was found that the introduction of job rotation had been experienced as positive in several regards, although the perceptions of stress and hurry were the same at follow-up.     

Optimal designs for compartmental models with correlated observations

The flow of internally deposited radioisotope particles inside the body of people exposed to inhalation, ingestion, injection or other ways is usually evaluated using compartmental models (see Sánchez & López-Fidalgo, (2003, and López-Fidalgo & Sánchez, 2005). The International Commission on Radiological Protection (ICRP, 1994) describes the model of the human respiratory tract, represented by two main regions. One of these, the thoracic region (lungs) is divided into different compartments. The retention in the lungs is given by a large combination of ratios of exponential sums depending on time. The aim of this work is to provide optimal times for making bioassays when there has been an accidental radioactivity intake and there is interest in estimating it. In this paper, a large two–parameter model is studied and a simplified model is proposed in order to obtain optimal designs in a more suitable way. Local c-optimal designs for the main parameters are obtained using the results of López-Fidalgo & Rodríguez-Díaz, 2004). Efficiencies for all the computed designs are provided and compared.     

Nonparametric maximum likelihood estimation of population size based on the counting distribution

Summary.  The paper discusses the estimation of an unknown population size n . Suppose that an identification mechanism can identify n _obs cases. The Horvitz–Thompson estimator of n adjusts this number by the inverse of 1− p ₀, where the latter is the probability of not identifying a case. When repeated counts of identifying the same case are available, we can use the counting distribution for estimating p ₀ to solve the problem. Frequently, the Poisson distribution is used and, more recently, mixtures of Poisson distributions. Maximum likelihood estimation is discussed by means of the EM algorithm. For truncated Poisson mixtures, a nested EM algorithm is suggested and illustrated for several application cases. The algorithmic principles are used to show an inequality, stating that the Horvitz–Thompson estimator of n by using the mixed Poisson model is always at least as large as the estimator by using a homogeneous Poisson model. In turn, if the homogeneous Poisson model is misspecified it will, potentially strongly, underestimate the true population size. Examples from various areas illustrate this finding.