CALL CENTERS (CENTRES) - Faculty of Industrial Engineering and ...

Abstract. Concerns the development for mail order company L.L. Bean of a computerized
procedure for selecting complex large-scale telephone-operator scheduling systems. To assess
capability in forecasting work load, setting requisite capacity levels, and generating satisfactory
work-shift schedules, cost/benefit analysis was used and the expected penalty costs of lost orders
due to understaffing and loaded-wage costs of overstaffing were considered. Queuing theory was
used to model customer-call behavior for every hour over 24-hour days, seven days per week, and
the results of linear regression, which correlated customer-service level with expected customer
abandonment rate, were implemented to estimate the impact on order revenues of telephoneservice
level.
Keywords: Work load forecasting, Queueing theory, Telephone agent scheduling system, Mailorder
company, L.L. Bean, Computerized procedure, Complex large-scale telephone operator
scheduling systems, Capacity levels, Work shift schedules, Cost-benefit analysis, Expected
penalty costs, Understaffing, Loaded wage costs, Overstaffing, Linear regression
(Appears also in Section VIII.)
23. Green, L. and P. Kolesar. Testing the validity of a queueing model of police patrol, Management
Science, 35 (2), 1989, 127–148.
Abstract. This paper describes efforts to validate a multiple car dispatch queueing (MCD)
model of police patrol operations using New York City data. The MCD model was designed for
use in a computer system that has been disseminated to many police departments in the U.S.
to help planners allocate patrol cars among precincts. It has also been used to evaluate specific
changes in patrol policy in New York. We define validation as a series of hierarchical procedures
ranging from tests of mathematical correctness to evaluations of model robustness. We discuss
the difficulties and limitations of assessing the validity of a model of a loosely managed system
in which human behavior is central and in which controlled experiments cannot be performed.
Focusing on specific uses, we conclude that the MCD model is a good although imperfect description
of patrol operations in New York and is a potentially useful planning tool for many
other urban police departments.
Keywords: Queueing, Validation, Police patrol, Multiple car dispatch queueing model, New
York City, Hierarchical procedures, Mathematical correctness, Model robustness, Urban police
departments
24. Blake, R.H., S.C. Graves and P.C. Santos. A model for the configuration of incoming WATS
lines, QUESTA, 7, 1990, 3–21.
Abstract. WearGuard is a direct marketer and retailer of uniforms and work clothes, which
relies primarily on phone orders for sales. For this purpose it maintains a series of toll-free “800number”
lines, known as WATS lines, to receive its incoming calls. These lines are of several
types, where each type serves a different portion of the country and has a different usage fee.
In this paper, we determine how many of each type of WATS lines should be employed. After
defining the problem more completely, we develop a queueing model to describe the system and a
dynamic program to solve the configuration problem to optimality. The model has been applied
to the problem by WearGuard since 1984. We present an example and examine the sensitivity
of the solution to variations in various parameters. We validate the model by comparing the
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