Research Reports from the Department of Operations
Document Type
Thesis
Publication Date
7-16-1980
Abstract
Whenever customers must queue for a service, waiting time and server utilization problems can result . In a labor intensive industry, the healthcare industry, these problems and their solution are important for they can effect a patient's welfare. A computer simulation model of an actual outpatient clinic function was developed to assist hospital management in developing selection parameters which are used to prioritize scheduled customers (based on their arrival time) and their service so as to reduce the waiting time of on-time customers. The model is an event-oriented simulator with scheduled and unscheduled arrivals. Scheduled arrivals are classified early, an-time, or late, based upon actual arrival times and two preselected parameters, A and 3. The parameters A and B define an interval (S-B, S+A) about each appointment time S within which arrivals with appointments at S are considered on-time. On-time customers are served with nonpreemptive priority over late and walk-in customers who are served with non preemptive priority over early customers. Also starting at S-B, freed-up servers are held open for expected customers with appointments at time S. The model permits the user to adjust the number of servers and the arrival generation, customer classifications, and processing time generation. Waiting time statistics for each customer classification and server utilization statistics are computed enabling the user to explore various strategies. In this particular investigation, interactions between the model's major user-defined parameters such as the customer arrival distributions, the number of servers, the customer lateness and processing times are investigated for their effects upon two criteria, server idleness and customer waiting time. These interactions are investigated principally for a system of 3 servers and 4 scheduled appointments per hour for each server. The results strongly confirm the obvious truism that the appointment time intervals should be based upon the average length of the processing time for each customer, and that customers- should be encouraged to arrive as close as possible to their scheduled arrival. time since this min#74'es overall customer waiting time and increases server utilization. Also, it was found that 3 servers provided the best balance between server utilization and customer waiting time overall, for the input parameters assumed. An investigation of the values of parameters A and B and their effects upon customer waiting time and server utilization are presented. For this study, the values of A and B were arbitrarily chosen in ratios of 1 to 1, 1 to 2, and 2 to 1. This was done to investigate the relative effects of the values of A to B as well as the absolute effects of the value of the sum of parameters A and B on the mean customer waiting times and server utilization. Results of the study suggest that a 2 to 1 ratio of the value of parameter A to parameter B generally provides lower customer waiting times and better server utilization than either equal values of parameters A and B, or a 2 to1 ratio of parameter B to A.The results of the analysis also indicate that the values of A between 2.5 and 3.5 minutes coupled with values of B between 5 and 7 minutes provide the lowest customer waiting times and the best server utilization for this serving configuration.
Keywords
Operations research, Queueing theory, Hospitals--Waiting lists, Medical appointments and schedules--Mathematical models, Health services administration, Simulation methods, Service industries--Management, Business--Mathematical models, Computer-generated simulations as evidence
Publication Title
Master's thesis/Technical Memorandums from the Department of Operations, School of Management, Case Western Reserve University
Issue
Technical memorandum no. 484 ; Submitted in partial fulfillment of the requirements for the Degree of Master of Science.
Rights
This work is in the public domain and may be freely downloaded for personal or academic use
Recommended Citation
Austin, Bruce L., "Computer Simulation of a Multiple Server Queue with Scheduled and Nonscheduled Arrivals" (1980). Research Reports from the Department of Operations. 89.
https://commons.case.edu/wsom-ops-reports/89