Comparison of a branch-and-bound heuristic,a newsvendor-based heuristic and periodic Bailey rules for outpatients appointment scheduling systems

Appointment-based service systems admit limited number of customers at a specific time interval to make service providers more accessible by reducing customers’ waiting time and make the costly resources more productive. A traditional approach suggests the Bailey rule, which assigns one or more customers at the initial block and only one customer at remaining blocks. We prescribe two heuristic approaches and variations of the traditional Bailey rule to appointment scheduling systems with the objective of minimizing total expected costs of delay and idle times between blocks. The first heuristic adopts a branch-and-bound approach using forward dynamic programming and tries to fully enumerate with some restrictions. The second heuristic uses a sequential-inverse newsvendor approach using a starting solution. We conduct numerical tests, which show that both heuristics get near-optimal solutions in a quicker time than a commercial solver, CPLEX and that the second approach gives near-optimal solutions far faster than the first approach. In addition, we suggest the use of a periodic Bailey rule, which can be implemented easily in practice, and provides a close solution to the best result of both heuristics, depending upon cost parameters and service-time variances.     

Optimal scheduling policies in time sharing service systems

We consider optimal scheduling problems in a TSSS (Time Sharing Service System), i.e., a tandem queueing network consisting of multiple service stations, all of which are served by a single server. In each station, a customer can receive service time up to the prescribed station dependent upper bound, but he must proceed to the next station in order to receive further service. After the total amount of the received services reaches his service requirement, he departs from the network. The optimal policy for this system minimizes the long-run average expected waiting cost per unit of time over the infinite planning horizon. It is first shown that, if the distribution of customer's service requirement is DMRL (Decreasing Mean Residual Life), the policy of giving the highest priority to the customer with the most attained service time is optimal under a set of some appropriate conditions. This implies that any policy without interruptions and preemptions of services is optimal. If the service requirement is DFR (Decreasing Failure Rate), on the other hand, it is shown that the policy of giving the highest priority to the customer with the least attained service time, i.e., the so-called LAST (Least Attained Service Time first) is optimal under another set of some appropriate conditions. These results can be generalized to the case in which there exist multiple classes of customers, but each class satisfies one of the above sets of conditions.     

Outpatient appointment scheduling in presence of seasonal walk-ins

This study investigates appointment systems (AS), as combinations of access rules and appointment-scheduling rules, explicitly designed for dealing with walk-in seasonality. In terms of ‘access rules’, strategies are tested for adjusting capacity through intra-week, or monthly seasonality of walk-ins, or their combined effects. In terms of ‘appointment rules’, strategies are tested to determine which particular slots to double-book or leave open in cases where seasonal walk-in rates exceed or fall short of the overall yearly rate. In that regard, this study integrates capacity and appointment decisions, which are usually addressed in an isolated manner in previous studies. Simulation optimization is used to derive heuristic solutions to the appointment-scheduling problem, and the findings are compared in terms of in-clinic measures of patient wait time, physician idle time and overtime. The goal is to provide practical guidelines for healthcare practitioners on how to best design their AS when seasonal walk-ins exist.     

The impact of multi-skilling on personnel scheduling in the service sector: a retail industry case

Using personnel scheduling to reduce overstaffing and understaffing in a service industry across multiple periods is often undermined by lack of flexibility due to the exclusive use of specialized personnel. This study analyses the impacts of assigning multi-skilled personnel to different activities and its potential for improving schedule efficiency. A proposed mixed integer linear programming model determines which employees are trained to work in which activities and their assignments over a one-week planning horizon. The model results show that the lowest total-cost multi-skilled configurations are obtained in scenarios where personnel supply and demand are in equilibrium. Half of employees would continue to be specialized for just one activity while the half slated for multi-skilling would be trained in most cases for just one additional activity, even though training cost is assumed to be minimal. It is also shown that multi-skilling is best applied to employees whose contracts are highly flexible.     

Evaluating the performance of Swedish savings banks according to service efficiency

This article develops principles for an evaluation of the efficiency of a savings bank. It starts out from the observation that such a bank is less profit oriented than a commercial bank. The customer is a vital stakeholder to the savings bank implying a greater emphasis on customer service provision. We are using data envelopment analysis (DEA) as a method to consider the service orientation of savings banks. We thereby demonstrate how an evaluation of the performance of savings banks according to “service efficiency” differs from an evaluation based on the traditional “profit” or shareholder concept. We determine the number of Swedish savings banks being “service efficient” as well as the average degree of service efficiency in this industry.     

Revenue-maximizing pricing and scheduling strategies in service systems with flexible customers

We propose a model of service operations systems in which customers are heterogeneous both in terms of their private delay sensitivity and flexibility. A service provider maximizes revenue through jointly optimal pricing and steady-state scheduling strategies. We provide a complete analysis for this generally intractable problem. Interestingly, when one queue accommodates a large population of impatient customers, it may be desirable to strategically idle the server in the other queue, which is a phenomenon new to the literature.     

Evaluating the effects of distribution centres on the performance of vendor-managed inventory systems

This paper evaluates the effects of the distribution centre (DC) in a vendor-managed inventory (VMI) system comprising one manufacturer, one DC and n retailers. Adopting the order-up-to-level (OUL) replenishment policy, the system aims to maximize the overall system profit. We propose a model to evaluate the system performance by considering the scale of the distribution network, influential cost factors, demand distribution, planning horizon, and facility locations. From the viewpoint of a supply chain, we examine the DC’s effects on the system in terms of net profit. Our findings reveal that the DC has effects on demand variance and system profit, and there are some dominant factors that affect the overall system performance. The DC may lead to different system performance under a variety of cost factors, and in some situations, the DC may negatively affect system performance. We also suggest some innovative uses of the DC’s location to help enhance system performance.     

Analysis of quota assignment and time block duration in multi-block appointment systems

The objective of this study is to propose performance evaluatorsand optimizers for the quota appointment system in many hospitalsand clinics used to smooth the patient flow. This type of queueingsystem with finite population and controlled arrivals is studiedon a single server with exponential service time. Given a targetwaiting time set by the hospital, the quota assignment givingthe minimum chance of underachievement in each time block isderived using a dynamic programming approach. This enables exactcalculations of performance measures of expected waiting time,server overtime and congestion measured in headcount. The optimaltime block duration, in addition to the quota assignment, isexamined using an extended dynamic programming formulation.Special cases of absentees, late arrivals and re-entry patientsare then incorporated into the basic model. Performance measuresare evaluated through two approaches, according to the prioritiesof treatment for the special cases.     

Evaluating the performance of Brazilian university hospitals

In order to demonstrate how DEA modeling can be helpful to aid decision making relative to the Brazilian Teaching Hospital Policy by means of hospital performance assessment, we develop a case study with 30 general hospitals linked to Brazilian Federal Universities. We consider data on medical care (Medical Model—MM), teaching and research (Teaching-Research Model—TRM) and use the software IDEAL (Interactive Data Envelopment Analysis Laboratory) as a tool for the units’ efficiency evaluation. IDEAL, developed in Brazil, is unique in providing a 3-D frontiers visualization, assisting in exploratory analysis and allowing a better understanding of the DEA modeling (envelopment and multiplier). Both models are input-oriented and each hospital is categorized according to its relative efficiency in the MM and TRM. In this phase, it is very important to discuss with the decision-makers the results and patterns of the DEA models. Finally, the modelling indicates the necessary changes for the inefficient units and generates recommendations for teaching ratios and public financing.     

Evaluating the financial performance of bank branches

We evaluate the financial performance of most of the branch offices of a large European savings bank for a recent accounting period. We employ a complementary pair of nonparametric techniques to evaluate their financial performance, in terms of their ability to conserve on the expenses they incur in building their customer bases and providing customer services. We find variation in the ability of branch offices to perform this task, and agreement on the identity of the laggard branches. We then employ parametric techniques to determine that the list of indicators on which their financial performance is evaluated can be reduced without statistically significant loss of information to bank management. Both findings suggest ways in which the bank can increase the profitability of its branch network. A previous version of this paper was presented at CORE, Université Catholique de Louvain, Louvain-la-Neuve, Belgium, where we received many helpful comments from the audience. We are grateful to three referees for their helpful comments as well.     

The impact of operating environment on efficiency of public libraries

Central European Journal of Operations Research - Analysis of technical efficiency is an important tool in management of public libraries. We assess the efficiency of 4660 public municipal...     

Generalization of Johnson's and Talwar's scheduling rules in two-machine stochastic flow shops

The paper deals with the classical problem of minimizing the makespan in a two-machine flow shop. When the job processing times are deterministic, the optimal job sequence can be determined by applying Johnson's rule. When they are independent and exponential random variables, Talwar's rule yields a job sequence that minimizes the makespan stochastically. Assuming that the random job processing times are independent and Gompertz distributed, we propose a new scheduling rule that is a generalization of both Johnson's and Talwar's rules. We prove that our rule yields a job sequence that minimizes the makespan stochastically. Extensions to m-machine proportionate stochastic flow shops, two-machine stochastic job shops, and stochastic assembly systems are indicated.     

Benefits of a truck appointment system on the service quality of inland transport modes at a multimodal container terminal

Container terminals pay more and more attention to the service quality of inland transport modes such as tucks, trains and barges. Truck appointment systems are a common approach to reduce truck turnaround times. This paper provides a tool to use the truck appointment system to increase not only the service quality of trucks, but also of trains, barges and vessels. We propose a mixed integer linear programming model to determine the number of appointments to offer with regard to the overall workload and the available handling capacity. The model is based on a network flow representation of the terminal and aims to minimize overall delays at the terminal. It simultaneously determines the number of truck appointments to offer and allocates straddle carriers to different transport modes. Numerical experiments, conducted on actual data, quantify the benefits of this combined solution approach. Discrete-event simulation validates the results obtained by the optimization model in a stochastic environment.     

The impact of controllable production rates on the performance of inventory systems: A systematic review of the literature

The lot sizing problem has attracted the attention of researchers for more than a century, and it still belongs to the most relevant decision problems in many manufacturing companies. During the evolution of research on lot sizing, the seminal economic order quantity (EOQ) model proposed by Harris [1913. How many parts to make at once. Factory, the Magazine of Management, 10 (2), 135-136.] has remained the most popular model, despite its limitations. To support lot sizing decisions in practice, researchers have frequently extended Harris’ basic EOQ model to better reflect the characteristics of real production processes. One of these extensions is the consideration of controllable (variable) production rates, which gives production planners more flexibility in managing the build-up and depletion of inventory and in controlling costs.The aim of this paper is to provide a comprehensive and systematic overview of EPQ-type lot sizing models that consider controllable production rates. First, the paper proposes a conceptual framework that captures the characteristics of controllable production rates including the planning horizon (short vs. long term), the number of potential interventions per production run (one vs. multiple), the effect of controllable production rates on the performance of the inventory system (e.g., unit production costs, energy consumption, product quality), and the type of lot sizing model considered (e.g., two-stage models, multi-stage models, multi-item models). Secondly, the paper presents the results of a systematic literature review and evaluates the state-of-research of lot sizing models with controllable production rates. Based on the analysis of the literature, key trends are summarized and promising research opportunities are discussed.     

我国AB股双重上市公司经营业绩变化的实证分析

本文以46家在上海和深圳同时上市AB股的公司的样本,分析了公司实行双重上市前1年及其后4年的经营业绩的变化趋势以及股权结构和上市顺序对它的影响。研究表明,双重上市当年及其后4年经营业绩显著下降;股权结构和上市顺序对公司经营业绩影响明显。最后,文章提出了改善AB股公司经营业绩的对策建议。     

The effect of information on queue-scalping service systems

We consider an M/M/1 queueing system with a single queue scalper who makes profit by selling his position in the queue. The equilibrium purchasing strategies of customers under observable case (with double-threshold strategy) and unobservable case (with mixed strategy) are derived. The profits of the queue scalper are obtained under two information levels. Numerical experiments suggest that the queue scalper is better off with unobservable case when the system is too congested or the operating cost is too low.     

Experimental investigation of real-time scheduling in flexible manufacturing systems

This paper presents a new two-phase (TP) approximate method for real-time scheduling in a flexible manufacturing system (FMS). This method combines a reduced enumeration schedule generation algorithm with a 0–1 optimization algorithm. In order to make the combined algorithm practicable, heuristic rules are introduced for the selection of jobs to be scheduled. The relative performance of the TP method vis-a-vis conventional heuristic dispatching rules such as SPT, LPT, FCFS, MWKR, and LWKR is investigated using combined process-interaction/discrete-event simulation models. An efficient experimental procedure is designed and implemented using these models, and the statistical analysis of the results is presented. For the particular case investigated, the conclusions are very encouraging. In terms of mean flow time, the TP method performs significantly better than any other tested heuristic dispatching rules. Also, the experimental results show that using global information significantly improves the FMS performance.