Estimation in proportional hazard and log-linear models

Proportional hazard models and models where the dependent variables follow a linear model are shown to be equivalent if and only if the hazard rate is the product of a non-negative periodic function and a Weibull factor. Estimates based on rank statistics are proposed for the parameters in the proportional hazard model.     

On variable bandwidth selection in local polynomial regression

The performances of data-driven bandwidth selection procedures in local polynomial regression are investigated by using asymptotic methods and simulation. The bandwidth selection procedures considered are based on minimizing 'prelimit' approximations to the (conditional) mean-squared error (MSE) when the MSE is considered as a function of the bandwidth h . We first consider approximations to the MSE that are based on Taylor expansions around h=0 of the bias part of the MSE. These approximations lead to estimators of the MSE that are accurate only for small bandwidths h . We also consider a bias estimator which instead of using small h approximations to bias naïvely estimates bias as the difference of two local polynomial estimators of different order and we show that this estimator performs well only for moderate to large h . We next define a hybrid bias estimator which equals the Taylor-expansion-based estimator for small h and the difference estimator for moderate to large h . We find that the MSE estimator based on this hybrid bias estimator leads to a bandwidth selection procedure with good asymptotic and, for our Monte Carlo examples, finite sample properties.     

A process evaluation of individual and organizational occupational stress and health interventions

There is reason to believe that many health and stress interventions fail due to inattention to the effects of intervention implementation processes, but evaluations of these processes are found only rarely in the literature. The objective of the present study was to explore the issue of obstacles to implementation that may occur when stress and health interventions are introduced in work organizations. The study was conducted as a process evaluation of seven different individual and organizational interventions. Interviews were conducted in 22 post offices, 12 organizational units (such as care homes and local administrative units) of a Norwegian municipality, and in 10 shops in a shopping mall. The interviews took place before and after the interventions. The following key process factors were identified: (1) the ability to learn from failure and to motivate participants; (2) multi-level participation and negotiation, and differences in organizational perception; (3) insight into tacit and informal organizational behaviour; (4) clarification of roles and responsibilities, especially the role of middle management; and (5) competing projects and reorganization. For improved studies of interventions in the future we recommend that qualitative and quantitative methods be combined, that researchers build more on natural interventions that occur naturally within the organization, and that a pilot study be undertaken in order to investigate the cultural maturity of the organization.     

Mutual Raiding of Production and the Emergence of Exchange

Joint exchange and raiding can emerge in a world of mutual raiding when the appropriated production is less valuable to the appropriator than to the defender and the defense is not too inferior to attack. The amounts of resources allocated to production and raiding and the amounts of goods exchanged reciprocally are determined endogenously. The model reduces to pure exchange and pure raiding as special cases. Pure exchange emerges when the usability of appropriation is sufficiently low. Pure raiding emerges if the defense is sufficiently inferior to attack. The results of the model are intermediate between the results of the two extreme cases.     

Sense of coherence: definition and explanation

The present study is one of a few that have used 'sense of coherence' (SOC) as a dependent variable in an explanatory model. After studying three different samples – 680 students, 180 parents and 315 couples – we conclude that family relational and psychopathological variables contribute significantly to the explanation of SOC (explained variance between 10–27 and 26–50 per cent). In total, we obtained an explained variance of between 42 and 64 per cent. This leads us to the conclusion that in all three samples, SOC is multifaceted and thereby is more than simply an opposite state to depression. Context may play an important part in the explanation of SOC.     

An appraisal of key factors in the implementation of occupational stress interventions

Empirical research on stress intervention in organizations, and experience from organizational change programmes in general, indicates that obtaining intended change is often more difficult than it had been conceived to be at the outset. In order to facilitate the accomplishment of stress prevention and effective organizational change, this paper examines the importance of the social and cognitive processes influencing the implementation of any intervention. It states that if change is to be managed skilfully, it is important (1) to create a social climate of learning from failure, (2) to provide opportunities for multi-level participation and negotiation in the design of interventions, (3) to be aware of tacit behaviours that possibly undermine the objectives of interventions, and (4) to define roles and responsibilities before and during the intervention period.     

Defense Resource Distribution Between Protection and Redundancy for Constant Resource Stockpiling Pace

The article considers the optimal resource distribution in a parallel system between increasing protection and providing redundancy in a situation when the attacker's and defender's resources are stockpiling and the resource increment rate is constant. It is assumed that the system must perform within an exogenously given time horizon and the attack time probability is uniformly distributed along this horizon. The defender optimizes the resource distribution in order to minimize the system destruction probability during the time horizon. First, we find the optimal pace of construction of the new redundant elements assuming that the construction must start in the initial stage of the stockpiling process. We show that starting construction of new elements in the beginning of the system's existence results in its high initial vulnerability. Introducing the time delay before starting the construction can reduce the initial system vulnerability and the entire system destruction probability. The problem of optimization of time delay and new element construction pace is considered with and without constraint on the initial system vulnerability. Examples illustrating the methodology of the optimal defense strategy analysis are presented.     

Learning difficulties and academic competence among children in contact with the child welfare system

Children who have been in the welfare system tend to have poor social and health outcomes as adults. The aim of this study was to examine learning difficulties, as well as academic competence, among children in contact with child welfare service, and to compare this group to their same‐age peers. The material consisted of 4114 children in fifth to seventh grade, of which 101 were in contact with child welfare services. Information on learning difficulties and academic competence was obtained through questionnaires to teacher and parent/caregivers. As expected, there were significantly more children with learning difficulties in the child welfare group than the peer group; 12% of child welfare clients had general learning difficulties compared to only 0.4% of their peers, and 31% had specific learning difficulties in relation to mathematics and/or reading and writing, compared to 10% of their peers. The majority of child welfare children received assistance from pedagogical–psychological services. While more than every second child welfare client without general learning disability had low academic competence, there were also 15% who had high academic competence. The results show that although many of the children in contact with child welfare service have learning difficulties, there is also heterogeneity and potential for academic achievement.