Scheduling for service Systems

Service oriented organizations, such as medical facilities, computer centers, or banks, face unique scheduling problems. These approaches are useful when the arrival of customers or jobs is random. Here we examine methods for scheduling personnel and facilities when the arrivals for service follow a dominant pattern. For example, if the arrivals of patients at a clinic follows a weekly pattern in which a larger number of patients arrive on Mondays and a smaller number arrive on Wednesdays, then we can use an appointment system and the appropriate scheduling of physician to meet the load. In all of these kinds of systems, demands for service and the time to perform the service may be highly variable. It often appears as though no sensible schedule can be constructed when arrivals for service and service times are random. One solution is to maintain the capability for service at capacity levels that are sufficient to keep the waiting line at certain acceptable average levels; thus the service facility is idle for some fraction of time so that service can be provided when it is needed. In a sense, the scheduling of the personnel and physical facilities is simple in such situations, being controlled by policies for the hours during which the service is to be offered and for the service level to be available. Schedules are then simple statements of “capacity for service” and personnel and other resources are keyed to these levels. The size of maintenance crews has often been determined on this basis.

Usually however, we can improve on the system response of simply “keeping hours”. Sometimes overall performance can be improved through the use of a priority system, talking arrivals on other than a first come first served basis. Also, improvements can often result examining the demand to see if there is a weekly and/or a daily pattern. When a pattern exists, it may be possible to schedule more effectively to improve service facility utilization, shorten average waiting time, or both. Thus, we have three broad groups of situations: the one described by random arrivals at a service center that performs a service requiring variable time, the one where priority systems are the basis for improved scheduling, and the one in which arrivals follow some dominant pattern.

The random arrival, variable service time case is the classic waiting line or queuing problem. When the distribution of arrivals and service times follow a certain known dominant pattern, we can use that information to schedule personnel and facilities.

The objective in scheduling personnel and work shifts is to minimize labor costs, given particular service standards, or to establish some happy compromise between labor costs and service standards. Although our emphasis will be on personnel and shift scheduling itself, it is important to recognize that shift scheduling is part of a larger process. The demand for the service must be forecast and converted to equivalent labor requirements by the hour of the day, the day of the week and so forth. Scheduling is then done in relation to these requirements. Finally, individual workers must be assigned to work days and shifts.

Suppose that we are faced with hourly requirements that vary from hour to hour, day to day, week to week, and so on. Staffing this operation would require continuous adjustment to the changing requirements. The demand variations might be caused by trend and seasonal factors, holidays, or weather conditions, depending on the nature of the particular operation. These kinds of personnel scheduling situation can be approached through the application of a simple concept, the ‘first hour principle. The first-hour principle can be stated as follows: Assign to start to work in the first period a number of workers equal to the number required for that period. For each subsequent period, assign the exact number of additional workers needed to meet requirements. When workers come to the end of their shifts, do not replace them if they are not needed. In practice specific charts are prepared by the service providing organization and the experienced supervisors/managers does a detailed scheduling.