Showing papers by "Mario Vanhoucke published in 2008"

Comparison and hybridization of crossover operators for the nurse scheduling problem

Abstract: In this paper, we present a hybrid genetic algorithm for the well-known nurse scheduling problem (NSP). The NSP involves the construction of roster schedules for nursing staff in order to maximize the quality of the roster schedule subject to various hard constraints. In the literature, several genetic algorithms have been proposed to solve the NSP under various assumptions. The contribution of this paper is twofold. First, we extensively compare the various crossover operators and test them on a standard dataset in a solitary approach. Second, we propose several options to hybridize the various crossover operators.

Diversity in resource consumption patterns and robustness of costing systems to errors

Abstract: Practitioners and academics hypothesize that when there is high diversity in resource consumption patterns, costing systems are more sensitive to errors. Given that firms' resources to enhance costing accuracy are typically constrained, it is argued that costing system refinement efforts should be focused on such cases, where they are likely to be most effective. However, little guidance is available on how to identify those situations where costing system refinement efforts (such as introducing an activity-based costing system) are likely to pay off most in terms of increased accuracy. Further, to our knowledge, the existing guidance provided by this high diversity rule of thumb has never been empirically tested. Using a simulation method, we address these issues in this paper. Specifically, we model various aspects, and degrees, of diversity in the resource consumption patterns to be reflected by the costing system and find that more diversity in resource consumption patterns only leads to increased cos...

Earned value forecast accuracy and activity criticality

Abstract: This paper presents new simulation results on the forecast accuracy of earned value based metrics to predict a project’s final duration. This is the second paper in a series of papers based on the simulation study initially proposed by Vanhoucke and Vandevoorde (2007b). In a previous manuscript published in the Measurable News (Vanhoucke and Vandevoorde, 2007a), it has been shown that the earned schedule method outperforms, on average, the more traditional earned value based methods to predict the final duration of a project, both for early and late projects. In the current manuscript, the simulation study is extended to new simulation scenarios that measure the influence of inaccuracies in the planned duration estimates for critical and non-critical activities on the accuracy of forecasting methods.

The effect of project schedule adherence and rework on the duration forecast accuracy of earned value metrics

Abstract: Earned Value Management (EVM) in project management integrates cost, schedule and technical performance and allows the calculation of cost and schedule variances, performance indices and forecasts of project cost and schedule duration. The earned value method provides early indicators of project performance to reveal opportunities and/or highlight the need for eventual corrective actions. The introduction of the earned schedule (ES) method in 2003 has led to an increasing attention on the forecast accuracy of EVM to predict a project's final duration. Previous research has shown that the ES method outperforms the more traditional predictive metrics for project duration forecasting. In this paper we critically review and test a novel ES extension, the p-factor approach, to measure schedule adherence based on the traditional earned value metrics. A large set of fictive project networks has been constructed under a controlled design and performance is measured by means of Monte Carlo simulations.

Diversity in resource consumption patterns and costing system robustness to errors

Abstract: Practitioners and academics hypothesize that when there is high diversity in resource consumption patterns, costing systems are more sensitive to errors. Given that firms' resources to enhance costing accuracy are typically constrained, it is argued that costing system refinement efforts should be focused on such cases, where they are likely to be most effective. However, little guidance is available on how to identify those situations where costing system refinement efforts (such as introducing an activity-based costing system) are likely to pay off most in terms of increased accuracy. Further, to our knowledge, the existing guidance provided by this high diversity rule of thumb has never been empirically tested. Using a simulation method, we address these issues in this paper. Specifically, we model various aspects, and degrees, of diversity in the resource consumption patterns to be reflected by the costing system and find that more diversity in resource consumption patterns only leads to increased costing system sensitivity to errors for some of the aspects of diversity studied. We also identify situations in which allocating costing system refinement resources to cases characterized by high diversity in resource consumption patterns is detrimental to improved accuracy.

Improved project time performance using activity sensitivity and network topology information

Abstract: The interest in activity sensitivity from both the academics and the practitioners lies in the need to focus a project manager's attention on those activities that influence the performance of the project. When management has a certain feeling of the relative sensitivity of the various parts (activities) on the project objective, a better management's focus and a more accurate response during project tracking should positively contribute to the overall performance of the project. In the current research manuscript, a simulation study is performed to measure the ability of four basic sensitivity metrics to dynamically improve the time performance during project execution. We measure the use sensitivity information to guide the corrective action decision making process to improve a project's time performance, while varying the degree of management's attention. A large amount of simulation runs are performed on a large set of fictive project networks generated under a controlled design.

Automatic Personalized Crew Rostering at Brussels Airlines

Abstract: In 2007, Brussels Airlines encountered a chronic shortage of pilots leading to a high and unbalanced workload, dissatisfied pilots, and a high turnover rate. The crew rostering process of Brussels Airlines is characterized as a manual preferential fair share process. The successful application of an operations research model in a pilot study to automate the crew rostering process indicated that the developed decision support system is able to reduce the overtime hours, and hence the workload, with 88 percent. This lead to an estimated reduction in personnel costs of 1.8 million euro. Moreover, the system was able to improve the fairness measured by different performance indicators by more than 40 percent which significantly increased the pilots’ job satisfaction. These excellent results instigated the management of Brussels Airlines to use the developed software as a simulation and bargaining tool in their negotiations with the pilot union. A wide range of scenarios were tested in order to determine the appropriate mix of pilot rostering rules improving the pilot working conditions.

Branching Strategies in a Branch-and-Price Approach for a Multiple Objective Nurse Scheduling Problem

Abstract: The efficient management of nursing personnel is of critical importance in a hospital’s environment comprising a vast share of the hospital’s operational costs. The nurse scheduling process affects highly the nurses’ working conditions, which are strongly related to the provided quality of care. In this paper, we consider the rostering over a mid-term period that involves the construction of duty timetables for a set of heterogeneous nurses. In scheduling nursing personnel, the head nurse is typically confronted with various (conflicting) goals complying with different priority levels, which represent the hospital’s policies and the nurses’ preferences. In constructing a nurse roster, nurses need to be assigned to shifts in order to maximize the quality of the constructed timetable satisfying the case-specific time related constraints imposed on the individual nurses’ schedules. Personnel rostering in healthcare institutions is a highly constrained and difficult problem to solve and is known to be NP-hard. In this paper, we present an exact branch-and-price algorithm for solving the nurse scheduling problem incorporating multiple objectives and discuss different branching and pruning strategies. Detailed computational results are presented comparing the proposed branching strategies and indicating the beneficial effect of various principles encouraging computational efficiency.

The Impact of Incorporating Nurse-Specific Characteristics in a Cyclical Scheduling Approach

Abstract: Nursing staff is principally cyclically scheduled in various hospitals in Belgium. The employed cyclic schedules embody, however, only a weak reflection of the ultimate nurse rosters constructed for a specific month. In this paper we investigate the benefits of integrating nurse-specific characteristics in the cyclic scheduling approach. Moreover, we analyze to what extent these characteristics should be incorporated and compare this approach with a general and more robust cyclical scheduling approach and the flexible acyclical rostering of nursing personnel.

Earned Value Forecast Accuracy and

Abstract: This paper presents new simulation results on the forecast accuracy of earned value based metrics to predict a project's final duration. This is the sec- ond paper in a series of papers based on the simulation study initially proposed by Vanhoucke and Vandevoorde (2007a). In a previous manuscript published in the Measurable News (Vanhoucke and Vandevoorde, 2007b), it has been shown that the earned schedule method outperforms, on average, the more traditional earned value based meth- ods to predict the final duration of a project, both for early and late projects. In the current manuscript, the simulation study is extended to new simulation scenarios that measure the influence of inaccuracies in the planned duration estimates for critical and non-critical activities on the accuracy of forecasting methods.