The employment adjustment of male immigrants in England

In this paper the employment performance of native and foreign born men in England is examined, using 1993–1994 data from the Quarterly Labour Force Survey of the United Kingdom. Chiswick's (1982) hypotheses of immigrant employment adjustment are investigated using logistic regression analysis. We show that there are interesting and important employment effects arising from immigrant characteristics. Recent white immigrants experience a transitory employment disadvantage. However non-white immigrants never attain employment equality with native born white men. Education, potential experience, family characteristics and country of birth are also found to be important determinants of employment. Received: 13 September 1998/Accepted: 15 July 1999     

Multiple Interacting Risk Factors: On Methods for Allocating Risk Factor Interactions

A persistent problem in health risk analysis where it is known that a disease may occur as a consequence of multiple risk factors with interactions is allocating the total risk of the disease among the individual risk factors. This problem, referred to here as risk apportionment, arises in various venues, including: (i) public health management, (ii) government programs for compensating injured individuals, and (iii) litigation. Two methods have been described in the risk analysis and epidemiology literature for allocating total risk among individual risk factors. One method uses weights to allocate interactions among the individual risk factors. The other method is based on risk accounting axioms and finding an optimal and unique allocation that satisfies the axioms using a procedure borrowed from game theory. Where relative risk or attributable risk is the risk measure, we find that the game‐theory‐determined allocation is the same as the allocation where risk factor interactions are apportioned to individual risk factors using equal weights. Therefore, the apportionment problem becomes one of selecting a meaningful set of weights for allocating interactions among the individual risk factors. Equal weights and weights proportional to the risks of the individual risk factors are discussed.     

Discounting Compensation for Injuries

The reasons commonly given for discounting future costs and benefits are doubtfully applicable to future injuries: in particular, time preference justifies neither inter- nor intragenerational discounting. The cost of future injuries could be discounted on grounds that a smaller sum, invested at interest, is needed to pay a given level of ex post monetary compensation the further in the future the injury occurs. This effect is offset, however, by the diminishing marginal utility of compensation, if consumption is otherwise increasing. Depending on the elasticity of marginal utility of consumption, on whether consumption is growing at an optimal rate, and on the time period considered, the implicit discount rate may be positive, zero, or negative (even indefinitely so). There is no prospect of conventional discounting dealing appropriately with the cost of injuries to either future or present generations.     

A Probabilistic Framework for the Reference Dose (Probabilistic RfD)

Determining the probabilistic limits for the uncertainty factors used in the derivation of the Reference Dose (RfD) is an important step toward the goal of characterizing the risk of noncarcinogenic effects from exposure to environmental pollutants. If uncertainty factors are seen, individually, as "upper bounds" on the dose-scaling factor for sources of uncertainty, then determining comparable upper bounds for combinations of uncertainty factors can be accomplished by treating uncertainty factors as distributions, which can be combined by probabilistic techniques. This paper presents a conceptual approach to probabilistic uncertainty factors based on the definition and use of RfDs by the US. EPA. The approach does not attempt to distinguish one uncertainty factor from another based on empirical data or biological mechanisms but rather uses a simple displaced lognormal distribution as a generic representation of all uncertainty factors. Monte Carlo analyses show that the upper bounds for combinations of this distribution can vary by factors of two to four when compared to the fixed-value uncertainty factor approach. The probabilistic approach is demonstrated in the comparison of Hazard Quotients based on RfDs with differing number of uncertainty factors.     

Optimal maintenance intervals for a multi-component system

In the manufacturing industry, preventive maintenance (PM) is carried out to minimise the probability of plant unexpected breakdown. Planned PM is preferred as disruption to operation is then minimised. Suggested PM intervals are normally prepared by the original equipment manufacturers (OEMs), however due to the multifaceted relationship between operating context and production requirement for different plants, it is unlikely that these suggested intervals as prescribed by the OEMs are optimal. Reliability, budget and breakdown outages cost are some of the critical factors that will affect the calculation of optimal maintenance intervals. Maintenance managers are required to determine optimal maintenance intervals with the above different requirements set by management. In this paper three models are proposed to calculate optimal maintenance intervals for multi-component system in a factory subjected to minimum required reliability, maximum allowable budget and minimum total cost. Numerical examples are provided to illustrate the application and usefulness of the proposed models.