A Conditional Likelihood Ratio Test for Structural Models

This paper develops a general method for constructing exactly similar tests based on the conditional distribution of nonpivotal statistics in a simultaneous equations model with normal errors and known reduced‐form covariance matrix. These tests are shown to be similar under weak‐instrument asymptotics when the reduced‐form covariance matrix is estimated and the errors are non‐normal. The conditional test based on the likelihood ratio statistic is particularly simple and has good power properties. Like the score test, it is optimal under the usual local‐to‐null asymptotics, but it has better power when identification is weak.     

Learning How and Learning What: Effects of Tacit and Codified Knowledge on Performance Improvement Following Technology Adoption

This paper examines effects of tacit and codified knowledge on performance improvement as organizations gain experience with a new technology. We draw from knowledge management and learning curve research to predict improvement rate heterogeneity across organizations. We first note that the same technology can present opportunities for improvement along more than one dimension, such as efficiency and breadth of use. We compare improvement for two dimensions: one in which the acquisition of codified knowledge leads to improvement and another in which improvement requires tacit knowledge. We hypothesize that improvement rates across organizations will be more heterogeneous for dimensions of performance that rely on tacit knowledge than for those that rely on codified knowledge (H1), and that group membership stability predicts improvement rates for dimensions relying on tacit knowledge (H2). We further hypothesize that when performance relies on codified knowledge, later adopters should improve more quickly than earlier adopters (H3). All three hypotheses are supported in a study of 15 hospitals learning to use a new surgical technology. Implications for theory and practice are discussed.     

AN IMPROVED HEURISTIC FOR STAFFING TELEPHONE CALL CENTERS WITH LIMITED OPERATING HOURS

Many telephone call centers that experience cyclic and random customer demand adjust their staffing over the day in an attempt to provide a consistent target level of customer service. The standard and widely used staffing method, which we call the stationary independent period by period (SIPP) approach, divides the workday into planning periods and uses a series of stationary independent Erlang‐c queuing models—one for each planning period—to estimate minimum staffing needs. Our research evaluates and improves upon this commonly used heuristic for those telephone call centers with limited hours of operation during the workday. We show that the SIPP approach often suggests staffing that is substantially too low to achieve the targeted customer service levels (probability of customer delay) during critical periods. The major reasons for SIPP‘ s shortfall are as follows: (1) SIPP's failure to account for the time lag between the peak in customer demand and when system congestion actually peaks; and (2) SIPP’ s use of the planning period average arrival rate, thereby assuming that the arrival rate is constant during the period. We identify specific domains for which SIPP tends to suggest inadequate staffing. Based on an analysis of the factors that influence the magnitude of the lag in infinite server systems that start empty and idle, we propose and test two simple “lagged” SIPP modifications that, in most situations, consistently achieve the service target with only modest increases in staffing.     

Coaching und Psychotherapie — Differenz und Konvergenz

Coaching and psychotherapy — difference and convergence. A discussion on counseling between professional and personal issuesThe author discusses the relation between coaching and psychotherapy. He emphasises several crucial differences, but here he is concerned with the interfaces between these formats. He demonstrates, that in many cases psychotherapeutic views — basing on corresponding qualifications — may offer an important improvement of coaching. This is illustrated by some case studies.     

Monte Carlo Sensitivity Analysis of Unknown Parameters in Hazardous Materials Transportation Risk Assessment

The US Department of Transportation was interested in the risks associated with transporting Hydrazine in tanks with and without relief devices. Hydrazine is both highly toxic and flammable, as well as corrosive. Consequently, there was a conflict as to whether a relief device should be used or not. Data were not available on the impact of relief devices on release probabilities or the impact of Hydrazine on the likelihood of fires and explosions. In this paper, a Monte Carlo sensitivity analysis of the unknown parameters was used to assess the risks associated with highway transport of Hydrazine. To help determine whether or not relief devices should be used, fault trees and event trees were used to model the sequences of events that could lead to adverse consequences during transport of Hydrazine. The event probabilities in the event trees were derived as functions of the parameters whose effects were not known. The impacts of these parameters on the risk of toxic exposures, fires, and explosions were analyzed through a Monte Carlo sensitivity analysis and analyzed statistically through an analysis of variance. The analysis allowed the determination of which of the unknown parameters had a significant impact on the risks. It also provided the necessary support to a critical transportation decision even though the values of several key parameters were not known.     

The Steiner Tree Problem in Kalmanson Matrices and in Circulant Matrices

We investigate the computational complexity of two special cases of the Steiner tree problem where the distance matrix is a Kalmanson matrix or a circulant matrix, respectively. For Kalmanson matrices we develop an efficient polynomial time algorithm that is based on dynamic programming. For circulant matrices we give an -hardness proof and thus establish computational intractability.     

Stress and Unemployment: A Comparative Review and Research Model of Female and Male Managers

This paper presents a multifaceted approach to unemployment stress experienced by male and female managers, in the form of a literature review and comparative research model. In order to develop a working model which can be applied to both male and female managers, the paper covers a substantial range of the literature pertaining to the processes and effects of unemployment for managers. Previous studies often provide conflicting data which generally results from differential approaches taken to the study of unemployment. In addition, it is important to note that the majority of studies focus on blue-collar male workers and that the vast majority are based on a male model of work. The proposed model highlights sources of stress, moderators of stress and stress outcomes that may affect unemployed managers, and distinguishes areas in which gender differences are likely to be found. However, these differences are only hypothesized from the current literature and require in-depth research if they are to be fully understood.     

Gender and physician-assisted suicide: an analysis of the Kevorkian cases, 1990-1997

This study examines the seventy-five suicide cases Dr. Jack Kevorkian acknowledged assisting during the period between 1990-1997. Although these cases represent a range of regional and occupational backgrounds, a significant majority are women. Most of these individuals had a disabling, chronic, nonterminal-stage illness. In five female cases, the medical examiner found no evidence of disease whatsoever. About half of the women were between the ages of forty-one and sixty, and another third were older adults. Men's conditions were somewhat less likely than women's to be chronic and nonterminal-stage. The main reasons for the hastened death mentioned by both the person and their significant others were having disabilities, being in pain, and fear of being a burden. The predominance of women among Kevorkian's assisted suicides contrasts with national trends in suicide mortality, where men are a clear majority. It is possible that individuals whose death was hastened by Kevorkian are not representative of physician-assisted suicide cases around the country, because of Kevorkian's unique approach. Alternatively, the preponderance of women among Kevorkian's assisted suicides may represent a real phenomenon. One possibility is that, in the United States, assisted suicide is particularly acceptable for women. Individual, interpersonal, social, economic, and cultural factors encouraging assisted suicide in women are examined.     

Psychosocial versus biomedical risk factors in Kevorkian's first forty-seven physician-assisted deaths

This article examines biomedical and psychosocial data on the first forty-seven cases of physician-assisted suicide (PAS) of Kevorkian as collected by means of both a physical autopsy and a preliminary psychological autopsy. The following patterns emerge: 1) The physical condition of these PAS patients was not typical of the conditions that lead to death in the United States. 2) Consistent with the above findings, our pilot data indicate that only 31.1 percent of these patients were terminal. While 73.9 percent were described as reporting pain, only 42.6 percent were revealed at autopsy to have a specific anatomical basis for their pain. However 36 percent were described as depressed, 66 percent as having some disability, and perhaps of key importance, 90 percent expressed a fear of dependency. Most important, our pilot data suggest the possibility of large gender differences, since 3) 68.1 percent of these forty-seven PAS's are women and only 31.9 percent are men. This represents the reverse of the gender pattern for completed suicides in the United States in 1995, resembling instead the approximate pattern for unsuccessful suicide attempts. 4) Approximately 75 percent of both men and women in the above sample were described as reporting pain. Men were almost twice as likely to have had an anatomical basis for the pain and three times as likely to be terminal. Our pilot data indicate PAS women are more likely to be described as depressed and twice as likely to have had a history of previous unsuccessful suicide attempts. 5) Kevorkian's patients were older than the typical unaided suicides in America. Reported pain decreases with age as does depression; however anatomical basis for pain increases slightly with age, and no age effect emerges for terminality. 6) Approximately two-thirds of those physician-assisted suicides were at middle SES levels. History of disability was the biggest risk factor for the low SES patients and fear of dependency for the high SES patients.