A Generalization of Wendell's Tolerance Approach to Sensitivity Analysis in Linear Programming

A criticism of linear programming has been that the data which are available in practice are too inexact and unreliable for linear programming to properly work. Managers are therefore concerned with how much actual values may differ from the estimates that were used in the model before the results become irrelevant. Sensitivity analysis emerged to help deal with the uncertainties inherent in the linear programming model. However, the ranges calculated are generally valid only when a single coefficient is varied. An extension of sensitivity analysis, the 100 Percent Rule, allows the simultaneous variation of more than one element in a vector, but does not permit the independent variation of the elements. A tolerance approach to sensitivity analysis enables the consideration of simultaneous and independent change of more than one coefficient. However, the ranges developed are unnecessarily restricted and may be reduced in width to zero when primal or dual degeneracy exists. This paper presents an extension of the tolerance approach which reduces the limitations of both the traditional and tolerance approaches to sensitivity analysis.     

Faculty Performance Evaluation: Modeling to Improve Personnel Decisions*

Based on likely future changes in faculty evaluation practices, this paper examines how institutions of higher education might operationalize performance evaluation as related to research, teaching, and service. A model is developed that allows coupling performance evaluation and relevant market considerations with merit pay, tenure, and promotion decisions. The approach is specifically applicable to tenure-track faculty members in colleges and universities.     

Multi-Item Grouping Algorithm Yielding Near-Optimal Logistics Cost

This article describes an algorithm used to formulate an inbound consolidation strategy when multi-items are replenished in groups and when total logistics cost is to be minimized. The importance of this algorithm is threefold (1) no optimal procedure exists for grouping multi-items when minimizing total logistics cost, (2) a complete enumeration of all possible groups (from which the optimal grouping set can be identified) is impractical due to the combinatorial nature of the grouping problem, and (3) no other heuristics have been developed that adequately reflect shipping cost in the analysis like this one does. We report the experience of using this algorithm to group and reorder 75 selected ensembles containing a total of 517 inventory items of a retail merchandising firm.     

Solution Procedures for the Lot-Streaming Problem

Lot streaming is the process of splitting a job into sublots so its operations can be overlapped and its progress accelerated. We present a computationally efficient procedure for solving the m-machine, two-sublot problem, and we discuss the bottleneck insights that emerge from the analysis. We also examine heuristic approaches for more than two sublots and discuss computational results for these procedures.     

Graphical representation of survival curves in the presence of time-dependent categorical covariates with application to liver transplantation

Graphical representation of survival curves is often used to illustrate associations between exposures and time-to-event outcomes. However, when exposures are time-dependent, calculation of survival probabilities is not straightforward. Our aim was to develop a method to estimate time-dependent survival probabilities and represent them graphically. Cox models with time-dependent indicators to represent state changes were fitted, and survival probabilities were plotted using pre-specified times of state changes. Time-varying hazard ratios for the state change were also explored. The method was applied to data from the Adult-to-Adult Living Donor Liver Transplantation Cohort Study (A2ALL). Survival curves showing a ‘split’ at a pre-specified time t allow for the qualitative comparison of survival probabilities between patients with similar baseline covariates who do and do not experience a state change at time t. Time since state change interactions can be visually represented to reflect changing hazard ratios over time. A2ALL study results showed differences in survival probabilities among those who did not receive a transplant, received a living donor transplant, and received a deceased donor transplant. These graphical representations of survival curves with time-dependent indicators improve upon previous methods and allow for clinically meaningful interpretation.     

Confidence intervals based on the deviance statistic for the hyperparameters in state space models

The main objective of this work is to evaluate the performance of confidence intervals, built using the deviance statistic, for the hyperparameters of state space models. The first procedure is a marginal approximation to confidence regions, based on the likelihood test, and the second one is based on the signed root deviance profile. Those methods are computationally efficient and are not affected by problems such as intervals with limits outside the parameter space, which can be the case when the focus is on the variances of the errors. The procedures are compared to the usual approaches existing in the literature, which includes the method based on the asymptotic distribution of the maximum likelihood estimator, as well as bootstrap confidence intervals. The comparison is performed via a Monte Carlo study, in order to establish empirically the advantages and disadvantages of each method. The results show that the methods based on the deviance statistic possess a better coverage rate than the asymptotic and bootstrap procedures.     

Prediction of future failures times based on Type-I hybrid censored samples of random sample sizes

In this article, we consider the prediction of future failure times based on Type-I hybrid censored samples. Point predictors and prediction intervals using different procedures are discussed for a general model. The exponential and Rayleigh distributions are used as illustrative examples to show the most simplified forms of the so obtained predictors as well as prediction intervals. Intensive simulation study and a real life dataset are presented to illustrate our findings and results.     

“Shifting the Power”: Youth Activists’ Narrative Reframing of the Immigrant Rights Movement

This article explores collective efforts by undocumented youth activists to use storytelling to reframe the debates around immigration reform and discursively position themselves as the rightful leaders of a movement that had been dominated by adult citizen‐advocates. Drawing on 19 months of fieldwork, 37 in‐depth interviews, and hundreds of pages of movement documents, I show how youth activists in the United States worked together to develop stories that: (1) drew into question the legitimacy of adult citizen‐advocates to speak on issues of immigration and (2) cast undocumented immigrant youth as the proper authorities on these matters. I argue that through collective storytelling and character work, the activists were able to subvert adult citizen authority and construct themselves as powerful, new collective actors in the contemporary immigrant rights movement. I conclude by discussing some of the practical implications and limitations of using narrative reframing strategies to advance the social change agendas of marginalized movement factions.     

Heterosexual Women’s Anal Sex Attitudes and Motivations: A Focus Group Study

Focus group methods were used to explore heterosexual women’s receptive anal sex attitudes and motivations. Behaviors under investigation included penile–anal intercourse (PAI), manual–anal stimulation, oral–anal contact, and the use of sex toys. A total of 33 self-identified heterosexual women ages 18 to 30 recruited from two metropolitan areas in the Midwestern United States participated in one of six focus groups. The findings suggest that women viewed heterosexual anal sex as an emerging norm. Attitudes and motivations were complex and varied by behavior. Dominant themes included curiosity, pain, pleasure, and stigma. Relational factors, including acquiescence, coercion, and consent, were also salient among participants. Factors that influence anal sexual behaviors may not be entirely distinct from those that influence other sexual behaviors; however, factors that influence anal intercourse may be distinct from those that influence nonintercourse anal sex. Improved understanding will allow scientists to better understand the integration of anal sex behaviors into the broader sexual repertoire.     

Clinical and Ethical Considerations for Delivering Couple and Family Therapy via Telehealth

Studies have generally supported telehealth as a feasible, effective, and safe alternative to in‐office visits. Telehealth may also be of particular benefit to couples/families interested in relational treatments, as it addresses some of the barriers that may be more prominent for families, such as childcare and scheduling difficulties. Therapists interested in expanding their practice to include telehealth should understand ethical and practical considerations of this modality. This article discusses areas unique to the delivery of telehealth to couples and families. Each broad domain is then elaborated upon with case examples from actual clinical practice and specific recommendations for addressing potential difficulties. Authors recommend further empirical research examining differences in modality outcome, as well as feasibility of the suggestions proposed here.