978-1285451374 Chapter 16 Solution Manual Part 1

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OM5 Chapter 16: Quality Control and SPC

Discussion Questions

1. Provide some examples in business or daily life in which a controlled process is

erroneously adjusted and an out-of-control process is ignored. What implications do

these errors have?

While it is clear that a truly out-of-control process must be corrected, many workers

mistakenly believe that whenever process output is off target, some adjustment must

be made. The stock market reacts to daily reports (often erroneously adjusting a

2. Discuss some examples of common and special causes of variation in your daily life

(for example, at school or at home).

Special (or assignable) cause variation arises from external sources that are not

inherent in the process, appear sporadically, and disrupt the random pattern of

common causes. Common cause variation is the inherent way the process is design

and what it is reasonably capable of. One example is commuting to and from school

3. Hospital administrators wanted to understand and better control the waiting time of

patients in the emergency room (ER) department. To do this, they constructed x-bar

and R-charts by sampling the waiting times of the first five patients admitted to the

ER at the beginning of each shift (7 a.m., 3 p.m., and 11 p.m.). What do you think of

this approach? Will it provide the information the hospital administrators seek? How

might the sampling process be improved, and what would you recommend?

This was an actual experience encountered by one of the authors. The purpose of

control charts is to understand the state of the process over time. Clearly 3 samples

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4. Suppose that you were monitoring the time it takes to complete order transactions at a

call center. Discuss what might cause such out-of-control conditions as a trend, shift

in the mean, or cycles in an x-bar chart in this situation.

An upward trend might occur as time passes during the day and more and more

people begin to call in. A shift in the average time might be the result of a new

5. Would it make sense to draw specification limits on an x-bar chart? Why or why not?

No, because specification limits relate to individual observations whereas an x-bar

chart monitors the average value of a sample. Instructors might refer to the sampling

Problems and Activities

Note: an asterisk denotes problems for which an Excel spreadsheet template on the

CourseMate Web site may be used.

Data sets for problems are also available on the CourseMate Website.

1. Develop a “personal quality checklist” on which you tally nonconformances in your

personal life (such as being late for work or school, not completing homework on

time, not getting enough exercise, and so on). What type of chart would you use to

monitor your performance?

This idea was promoted by an AT&T executive as a means of getting himself (and

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2. Examine the questions in the satisfaction survey in the box “Izzy’s: Measuring

Customer Satisfaction.” How do the questions relate to the five dimensions of

service quality introduced in Chapter 3? Discuss how the survey results could be

used to control quality. What types of quality control charts might be used?

Service quality is consistently meeting or exceeding customer expectations (external

focus) and service delivery system performance (internal focus) for all service

Service-quality measures are based primarily on human perceptions of service

collected from customer surveys, focus groups, and interviews. Chapter 3 introduced

1. Tangibles—Physical facilities, uniforms, equipment, vehicles, and appearance

of employees (i.e., the physical evidence).

Cleanliness

Restrooms clean & supplied?

2. Reliability—Ability to perform the promised service dependably and

accurately.

3. Responsiveness—Willingness to help customers and provide prompt recovery

to service upsets.

4. Assurance—Knowledge and courtesy of the service providers, and their

ability to inspire trust and confidence in customers.

5. Empathy—Caring attitude and individualized attention provided to its

customers.

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Employee attitude

Most questions deal with tangibles of the food and restaurant. There are no specific

3. Thirty samples of size 4 of the customer waiting time at a call center for a health

insurance company resulted in an overall mean of 10.4 minutes and average range of

0.9 minutes. Compute the control limits for – and R-charts.

From Appendix B: With n = 4 then A2 = 0.729, D3 = 0, D4 = 2.282

For the R-chart:

4.* Thirty samples of size 3, available in the worksheet C16P4 in the OM5 Data

Workbook were taken from a machining process over a 15-hour period. Construct

control charts using the Excel template xBar&R Chart. Verify the Excel calculations

of the control limits by hand using the formulas in the chapter. Does the process

appear to be in statistical control? Why or why not?

Mean = 3.526; Average range = 0.6733; A2 = 1.02; D4 = 2.57

x-bar chart:

Portions of the spreadsheet template are shown below:

x

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LCLx-bar

2.83718

Center

3.526

UCLx-bar

4.21482

LCLrange

0

Center

0.673333333

UCLrange

1.73316

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The R-bar chart appears to be in control but the x-bar chart seems to have a

5.* Tri-State Bank is investigating the processing time for loan applications. Samples

were taken for 25 random days from 4 branches. These data can be found in the

worksheet C16P5 in the OM5 Data Workbook. Construct control charts using the

Excel template xBar&R Chart. Verify the Excel calculations of the control limits

by hand using the formulas in the chapter. Does the process appear to be in

statistical control? Why or why not?

LCLx-bar

7.19928

Center

18.63

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UCLx-bar

30.06072

LCLrange

0

Center

15.68

UCLrange

35.78176

The average processing times (x-bar chart) are quite consistent; however, there

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Ask your students “What might cause the R-chart variability?” Closer inspection of

6. Twenty-five samples of loan applications at a bank, each of size 150, resulted in a

total of 22 errors. Compute the control limits for a p-chart.

p-bar = 22/[(25)(150)] = 22/3,750 = 0.00587

7.* One hundred insurance claim forms are inspected daily for 25 working days, and the

number of forms with errors are recorded in the worksheet C16P7 in the OM4 Data

Workbook. Construct a p-chart using the Excel template p-Chart. Verify the Excel

calculations of the control limits by hand using the formulas in the chapter. If any

special causes are identified, remove them from the data and construct a revised

control chart.

p-bar = 46/[(100)(25)] = 0.019

Portions of the Excel template are shown below:

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Samples 9 and 23 are outside of the control limits and are most likely due to a special

cause. If these are removed (by simply deleting the cells in column B of the