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chapter 12 managing waiting lines

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chapter 12 managing waiting lines

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    1. Chapter 12Managing Waiting Lines

    3. Learning Objectives Describe the economies of waiting lines using examples. Describe how queues form. Apply Maisters two laws of service. Describe the four psychology of waiting components and suggest strategies to deal with each. Describe the four principles of waiting line management. Describe the essential features of a queuing system. Describe the relationship between a negative exponential distribution of time between arrivals and a Poisson distribution of arrival rates.

    4. Where the Time Goes In a life time, the average person will spend: SIX MONTHS Waiting at stoplights EIGHT MONTHS Opening junk mail ONE YEAR Looking for misplaced 0bjects TWO YEARS Reading E-mail FOUR YEARS Doing housework FIVE YEARS Waiting in line SIX YEARS Eating

    5. Cultural Attitudes Americans hate to wait. So business is trying a trick or two to make lines seem shorter The New York Times, September 25, 1988 An Englishman, even when he is by himself, will form an orderly queue of one George Mikes, How to be an Alien In the Soviet Union, waiting lines were used as a rationing device Hedrick Smith, The Russians

    6. Waiting Realities Inevitability of Waiting: Waiting results from variations in arrival rates and service rates Economics of Waiting: High utilization purchased at the price of customer waiting. Make waiting productive (salad bar) or profitable (drinking bar).

    7. Laws of Service Maisters First Law:Customers compare expectations with perceptions. Maisters Second Law:Is hard to play catch-up ball. Skinners Law:The other line always moves faster. Jenkins Corollary:However, when you switch to another other line, the line you left moves faster.

    8. Remember Me I am the person who goes into a restaurant, sits down, and patiently waits while the wait-staff does everything but take my order. I am the person that waits in line for the clerk to finish chatting with his buddy. I am the one who never comes back and it amuses me to see money spent to get me back. I was there in the first place, all you had to do was show me some courtesy and service. The Customer

    9. Queueing System A queue is a line of waiting customers who require service from one or more servers. The queue need not be a physical line of individuals in front of a server (e.g., a person being placed on hold by a telephone operator)

    10. Queuing System-2 Queuing systems occur in a variety of forms: Servers need not be limited to serving one customer at a time. (e.g., buses, airplanes and elevators are bulk services) The consumer need not always travel to the service facility (e.g., fire, police protection, ambulance service)

    11. Queuing System-3 The service may consist of stages of queues in a serious or of a more complex network of queues (haunted-house attraction at amusement parks In any service systems, a queue forms whenever current demand exceeds existing capacity to serve.

    12. Psychology of Waiting That Old Empty Feeling: Unoccupied time goes slowly A Foot in the Door: Pre-service waits seem longer that in-service waits The Light at the End of the Tunnel: Reduce anxiety with attention Excuse Me, But I Was First: Social justice with FCFS queue discipline They Also Serve, Who Sit and Wait: Avoids idle service capacity

    13. Approaches to Controlling Customer Waiting Animate: Disneyland distractions, elevator mirror, recorded music Discriminate: Avis frequent renter treatment (out of sight) Automate: Use computer scripts to address 75% of questions Obfuscate: Disneyland staged waits (e.g. House of Horrors)

    14. Essential Features of Queuing Systems

    15. Arrival Process The rate at which customers arrive by the arrival process Any analysis of a service system must begin with complete understanding of the temporal and spatial distribution of the demand for that service. These data then are used to calculate interarrival times.

    16. Arrival Process-2 Many empirical studies indicate that the distribution of interarrival times will be exponential. The shape of the curve in Fig.12.3 is typical of the exponential distribution. The exponential distribution also can be recognized by noting that boat the mean and the standard deviation theoretically equal =2.4 and s=2.6 for Fig.12.3)

    17. Distribution of Patient Interarrival Times (Fig.12.3)

    19. Arrival Process-3 The exponential distribution for the data displayed in Fig.13.3 is f(t)= 0.4167e-0.4167t t=0 (3) F(t)= 1- e-0.4167t t=0 (4) Equation (4) can be used to find the probability that if a patient has already arrived, another will arrive in the next 5 minutes F(5) = 1- e-0.4167(5) = 0.876

    21. Arrival Process

    22. Temporal Variation in Arrival Rates

    23. Poisson and Exponential Equivalence Poisson distribution for number of arrivals per hour (top view) One-hour 1 2 0 1 interval Arrival Arrivals Arrivals Arrival

    24. Queue Configurations Queue configuration refers to the number of queues, their locations, their spatial requirements, and their effects on customer behavior. Fig. 12.9 (next slide) illustrates three alternative waiting configurations for a service.

    25. Queue Configurations

    26. Classifications of Queue Configurations

    27. Queue Discipline The queue is a policy established by management to select the new customer from the queue for service. The most popular service discipline is the first come, first serve (static rule) Dynamic queue disciplines are based on some attribute of the customer or status of the waiting line

    28. Queue Discipline-2 Shortest Processing Time (SPT) Rule has the property of minimizing the aveage time that customer spend in the system (e.g., Prof. might select the next student based on probably short activity time). c-rule: where, c=linear cost rate, =rate of customers served per unit time. This priority rule has the social optimization of objective of maximizing the sum of the benefits for customer plus provider.

    29. Queue Discipline-3 Preemptive Rule: under this rule, the service currently in process for a person is interrupted to serve a newly arrived customer with high priority. (e.g., emergency services) Round-Robin Rule: (e.g., dentists with multiple examination rooms. Fig.12.11 shows a classification of queue discipline.

    30. Queue Discipline

    31. Service Process The distribution of service times, arrangement of servers, management policies, and server behavior all contribute to service performance. Fig.12.12 containes histograms of several service time distributions in an outpatient clinic with x = 1/. The distribution of service times is a reflection of the variations in customer needs and server performances.

    32. Outpatient Service Process Distributions

    33. Service Facility Arrangements Table 12.1 (next slide) illustrates variety of service facility arrangements that are possible. With server in parallel, management gains flexibility in meeting the variations in demand for service. Another advantage of parallel servers is that they provide redundancy in case of equipment failure.

    34. Service Facility Arrangements Service facility Server arrangement Parking lot Self-serve Cafeteria Servers in series Toll booths Servers in parallel Supermarket Self-serve, first stage; parallel servers, second stage Hospital Many service centers in parallel and series, not all used by each patient

    35. Classifications of Service Processes

    36. Topics for Discussion Suggest some strategies for controlling variability in service times. Suggest diversions that could make waiting less painful. Select a bad and good waiting experience, and contrast the situations with respect to the aesthetics of the surroundings, diversions, people waiting, and attitude of servers. Suggest ways that management can influence the arrival times of customers. What are the benefits of a fast-food employee taking your order while waiting in line?

    37. Interactive Exercise The class breaks into small groups with at least one international student in each group, if possible. Based on overseas travel, each group reports on observations of waiting behavior from a cultural perspective.

    38. Thrifty Car Rental

    39. Eyell Be Seeing You How are Maisters First and Second Laws of Service illustrated? What good and bad features of a waiting process are evident? How should Dr. X respond to Mrs. Fs letter? How could Dr. X prevent future incidents? Should customers be rewarded for offering constructive criticism?

    40. Sample Letter Dear Mrs. F.: I offer my deepest apologies for your recent bad experience on January 5, 1989. The treatment you were shown and the length of time you had to wait is completely inexcusable. You and the rest of your family are valued patients of mine and I hope this most unfortunate experience does not cause me to lose your patronage. I personally guarantee that this will not happen again. I hope you will make another appointment with us to have your problem taken care of. This service, of course, will be provided free of charge. Thank you for expressing your concerns. Please let me know immediately if you have any other problems. Sincerely yours, Dr. X, M.D.

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