Analysis of the workload of bank tellers of a Brazilian public institution

During the last decades there have been many changes in the banking sector organization. It has been also observed the mutual growing of musculoskeletal and mental disorders. This study investigated the workload of bank tellers at a Brazilian public institution. It was performed the Ergonomic Work Analysis (EWA). Three employees participated in this study. During the analysis process, three research instruments were applied: Inventory of Work and Risk of Illness, Yoshitake Fatigue Questionnaire and Nordic Musculoskeletal Questionnaire, beyond the realization of footage recordings and the self-confrontation. The results indicated the existence of an excess of workload on the evaluated workstations, mainly in relation to mental order constraints, that overlaps the physical aspects. Thereby it was found that the employees tend to adopt strategies trying to reduce the impacts of the excess of workload, in order to regulate it.     

Bayesian inference for power law processes with applications in repairable systems

Statistical models for recurrent events are of great interest in repairable systems reliability and maintenance. The adopted model under minimal repair maintenance is frequently a nonhomogeneous Poisson process with the power law process (PLP) intensity function. Although inference for the PLP is generally based on maximum likelihood theory, some advantages of the Bayesian approach have been reported in the literature. In this paper it is proposed that the PLP intensity be reparametrized in terms of (β,η), where β is the elasticity of the mean number of events with respect to time and η is the mean number of events for the period in which the system was actually observed. It is shown that β and η are orthogonal and that the likelihood becomes proportional to a product of gamma densities. Therefore, the family of natural conjugate priors is also a product of gammas. The idea is extended to the case that several realizations of the same PLP are observed along overlapping periods of time. Some Monte Carlo simulations are provided to study the frequentist behavior of the Bayesian estimates and to compare them with the maximum likelihood estimates. The results are applied to a real problem concerning the determination of the optimal periodicity of preventive maintenance for a set of power transformers. Prior distributions are elicited for β and η based on their operational interpretation and engineering expertise.     

A Bayesian nonparametric model for Taguchi's on-line quality monitoring procedure for attributes

A Bayesian nonparametric model for Taguchi's on-line quality monitoring procedure for attributes is introduced. The proposed model may accommodate the original single shift setting to the more realistic situation of gradual quality deterioration and allows the incorporation of an expert's opinion on the production process. Based on the number of inspections to be carried out until a defective item is found, the Bayesian operation for the distribution function that represents the increasing sequence of defective fractions during a cycle considering a mixture of Dirichlet processes as prior distribution is performed. Bayes estimates for relevant quantities are also obtained.     

Inference for Parameters Defined by Moment Inequalities Using Generalized Moment Selection

The topic of this paper is inference in models in which parameters are defined by moment inequalities and/or equalities. The parameters may or may not be identified. This paper introduces a new class of confidence sets and tests based on generalized moment selection (GMS). GMS procedures are shown to have correct asymptotic size in a uniform sense and are shown not to be asymptotically conservative. The power of GMS tests is compared to that of subsampling, m out of n bootstrap, and “plug‐in asymptotic” (PA) tests. The latter three procedures are the only general procedures in the literature that have been shown to have correct asymptotic size (in a uniform sense) for the moment inequality/equality model. GMS tests are shown to have asymptotic power that dominates that of subsampling, m out of n bootstrap, and PA tests. Subsampling and m out of n bootstrap tests are shown to have asymptotic power that dominates that of PA tests.     

Middle Childhood Feelings Toward Mothers: Predictions From Maternal Directiveness at the Age of Two and Respect for Autonomy Currently

The goals of this study were to examine (1) stability of maternal directiveness during interactions with their children from toddlerhood to late middle childhood, (2) direct and mediated relations between mothers' directiveness when children were two years old, mothers' respect for autonomy and children's positivity and negativity toward their mothers when children were in late middle childhood, and (3) differences in these paths by ethnoracial group. Participants included 876 European‐American, 789 African‐American, and 411 Mexican‐American mothers and their children from the Early Head Start Research and Evaluation Project. Maternal respect for autonomy at Time 2 partially mediated an association between Time 1 directiveness and observed child positivity toward mothers at Time 2. There was also a direct inverse link between Time 1 maternal directiveness and children's observed positivity toward mothers at Time 2. Relations were similar across ethnoracial groups and for boys and girls. The discussion focuses on heterotypic stability in directive parenting and its implications for children's feelings toward their mothers.     

Similarity and the Quality of Online and Offline Social Relationships Among Adolescents in Israel

Studies on online social relationships have focused on how Internet use is associated with sociability, but have not compared the quality of online with offline relationships. On the other hand, studies on adolescent friendship formation have used school samples disregarding the Internet as a new social context for it. We took a different approach, studying the relationship between the social context of acquaintance (school, neighborhood, and online) and the structure and quality of friendships among adolescents. In a representative sample of Israeli adolescents (n=980), similarities in age, gender, and place of residence were studied in respect of the social sphere in which each friend was met (neighborhood, school, and online communication). We found that when a friend was met at school the likelihood of similarity in age, gender, and place of residence was higher than when contact was made online. Friends met in the neighborhood and schools were usually closer than friends met online. However, social similarity mattered even for friends who were met online. The more similar an online friend was in residence and gender, the stronger was the social tie.     

Moral Development in Adolescence

Themes in the papers in this special issue of the JRA on moral development are identified. We discuss the intersection of moral development research with policy concerns, the distinctive qualities of moral life in adolescence that warrant investigation, the multiple connotations of “moral,” the methods typical of moral development research, and the influences that shape adolescent moral development. Suggestions are made for new methods and new directions in the study of moral development.     

The Role of Emotional Reactivity,Self‐regulation,and Puberty in Adolescents' Prosocial Behaviors

This study was designed to examine the roles of emotional reactivity, self‐regulation, and pubertal timing in prosocial behaviors during adolescence. Participants were 850 sixth graders (50 percent female, mean age = 11.03, standard deviation = .17) who were followed up at the age of 15. In hierarchical regression models, measures of emotional reactivity, self‐regulation, pubertal timing, and their interactions were used to predict (concurrently and over time) adolescents' prosocial behaviors in the home and with peers. Overall, the findings provide evidence for pubertal and temperament‐based predictors of prosocial behaviors expressed in different contexts. Self‐regulation was positively related to both forms of prosocial behavior, concurrently and longitudinally. Emotional reactivity showed moderately consistent effects, showing negative concurrent relations to prosocial behavior with peers and negative longitudinal relations (4 years later) to prosocial behavior at home. Some curvilinear effects of temperament on prosocial behaviors were also found. Effects of pubertal timing were found to interact with gender, such that boys who were early maturers showed the highest levels of prosocial behavior at home concurrently. Discussion focuses on the role of temperament‐based mechanisms in the expression of prosocial behaviors in different contexts in adolescence.     

A control chart for variance based on squared ranks

A nonparametric control chart for variance is proposed. The chart is constructed following the change-point approach through the recursive use of the squared ranks test for variance. It is capable of detecting changes in the behaviour of individual observations with performance similar to a self-starting CUSUM chart for scale when normality is assumed, and a relatively better power when assessing nonnormal observations. A comparison is also made with two equivalent nonparametric charts based on Mood and Ansari-Bradley statistics. When dealing with symmetrical distributions, the proposed chart shows smaller (better) out-of-control average run length (ARL), and a competing performance otherwise. In addition, sensitivity to changes in mean and variance at the same time was tested. Extensive Monte Carlo simulation was used to measure performance, and a practical example is provided to illustrate how the proposed control chart can be implemented in practice.     

Optimal Maintenance Time for Repairable Systems Under Two Types of Failures

Determination of preventive maintenance is an important issue for systems under degradation. A typical maintenance policy calls for complete preventive repair actions at pre-scheduled times and minimal repair actions whenever a failure occurs. Under minimal repair, failures are modeled according to a non homogeneous Poisson process. A perfect preventive maintenance restores the system to the as good as new condition. The motivation for this article was a maintenance data set related to power switch disconnectors. Two different types of failures could be observed for these systems according to their causes. The major difference between these types of failures is their costs. Assuming that the system will be in operation for an infinite time, we find the expected cost per unit of time for each preventive maintenance policy and hence obtain the optimal strategy as a function of the processes intensities. Assuming a parametrical form for the intensity function, large sample estimates for the optimal maintenance check points are obtained and discussed.