Multi-item production lot-size inventory model with varying order cost under a restriction: A geometric programming approach

In this paper we present a geometric programming approach for determining the inventory policy for multiple items having varying order cost, which is a continuous function of the order quantity, and a limit on the total average inventory of all items. Our model is a generalization of that of Gupta and Gupta for unrestricted single-item order quantity model with varying order cost and assumes the same order cost function. This cost function relates well to real-life situations since it increases as the order quantity increases and, at the same time, it is easy to handle when deducing previous work as special cases of our model since it is easily reducible to a constant. An example is solved to illustrate the method.     

Call Center Delay Announcement Using a Newsvendor‐Like Performance Criterion

The problem of estimating delays experienced by customers with different priorities, and the determination of the appropriate delay announcement to these customers, in a multi‐class call center with time varying parameters, abandonments, and retrials is considered. The system is approximately modeled as an M(t)/M/s(t) queue with priorities, thus ignoring some of the real features like abandonments and retrials. Two delay estimators are proposed and tested in a series of simulation experiments. Making use of actual state‐dependent waiting time data from this call center, the delay announcements from the estimated delay distributions that minimize a newsvendor‐like cost function are considered. The performance of these announcements is also compared to announcing the mean delay. We find that an Erlang distribution‐based estimator performs well for a range of different under‐announcement penalty to over‐announcement penalty ratios.     

Combining non-linear regressions that have unequal error variances and some parameters in common

Methods of estimation and inference are presented for the situation where two non-linear regression models with unequal error variances contain some parameters in common. Such a situation arises in structural chemistry, when bond lengths are available for three nearly collinear atoms in crystals and a model is required to quantify the extent and form of the relationship between the longer and the shorter bond. Some atomic triples are symmetric and require a different model and error variance from those required by the asymmetric triples. The profile likelihood for the regression parameters is a weighted sum of the logarithms of the sums-of-squares functions from each model, and the estimates can be obtained by using a simple modification to a standard non-linear least squares program. A likelihood ratio test for assessing whether the parameters in common are equal is described. When these techniques are applied to two data sets consisting of bond lengths for bromine–tellurium–bromine and sulphur–tellurium–sulphur triples, there is no evidence against the equality hypothesis. An extension to the model to allow for a non-constant variance is required for proper analysis of the sulphur–tellurium–sulphur data.     

Acquired immune deficiency syndrome projections in England and Wales: interplay of methodology and data

Since the late 1980s, regular monitoring of the human immunodeficiency virus epidemic in England and Wales has been carried out through the work of successive national working groups. One of their tasks has been to provide short-term projections of the incidence of acquired immune deficiency syndrome. In this paper the data and methods used in this projection work are reviewed and results critically assessed with the aim of highlighting the strong interaction between methodological developments and data acquisition.     

Markov-chain monte carlo: Some practical implications of theoretical results

We review and discuss some recent progress in the theory of Markov-chain Monte Carlo applications, particularly oriented to applications in statistics. We attempt to assess the relevance of this theory for practical applications.     

Correlates of the Randolph Attachment Disorder Questionnaire (RADQ) in a Sample of Children in Foster Placement

This study examined mental health and attachment problems in children in foster care. This study also obtained data concerning the validity of the Randolph Attachment Disorder Questionnaire (RADQ). Children were selected according to length of time in placement and age and screened for mental health symptoms using the Child Behavior Checklist and the RADQ. The findings showed that children in foster care have reported symptoms within the range typical of children not involved in foster care. The conclusion is that the RADQ has limited usefulness due to its lack of specificity with implications for treatment of children in foster care.     

How important is your personality? Labor market returns to personality for women in the US and UK

Why do apparently similar people have varied success in the labor market? While cognitive performance and educational attainment have been shown to be strong indicators of economic success, there remains a large portion of unexplained variance in earnings after controlling for the standard variables. This paper uses the National Longitudinal Survey of Young Women and women from the National Child Development Study to explore the value of incorporating psychological traits into wage determination models. This research finds that traits such as locus of control, aggression, and withdrawal are all statistically significant factors in the wage determination models of white women.     

An E-mail assessment of undergraduates' attitudes toward smoking.

Responses from 513 of 1,000 randomly selected undergraduate students who were sent an e-mail questionnaire, about cigarette smoking were analyzed. Thirteen percent of the respondents identified themselves as smokers. No statistically significant differences were observed between smokers and nonsmokers and year in college, sex, age, race, or having attended public or private high schools. Ninety-eight percent of the respondents considered themselves knowledgeable about adverse health consequences of smoking, yet 39.1% of current smokers seriously considered stopping smoking, and 11.5% of current nonsmokers intended to start smoking. The preferred quitting method of smokers and ex-smokers was stopping all at once ("cold turkey"). Fifty-two percent of the smokers did not want professional assistance to stop smoking; 40% of the nonsmokers wanted information on second-hand smoke.