Statistical Quality Design and Control DeVor/Chang/Sutherland
Solutions to Chapter 1 Exercises
1.1 Explain the change in the view of quality control in the United States between the decades of the 1950s, 60s,
70s, and today.
Quality control before the 1980's was characterized by:
• the need to keep bad parts from reaching the customer, mostly through the use of mass inspection techniques.
• employing the QC department as a policing function trying to catch bad product before it goes out the door.
• constant "fire-fighting", frantically trying to solve each new problem as it would arise.
• the drive to meet the acceptable standard of productivity, often typified by the work standard, and the acceptable
level of quality, often articulated in terms of an "acceptable quality level" (AQL).
From the 1980's to the present, quality control has:
• employed statistics to identify improvement opportunities in the process.
• emphasized the continual improvement in both quality and productivity.
• begun to work side-by-side with manufacturing to produce a better product and enhance the company's
competitive position.
• begun to shift away from quality as primarily a manufacturing-based concept to quality as a design-based
concept as well, i.e., pushing the quality efforts of the organization farther upstream into engineering design.
1.2 What changes must take place for the United States to become competitive again in the world marketplace?
To again become competitive in the world marketplace, the U.S. must:
• institute a process control philosophy which enables both quality and productivity to increase simultaneously.
• expand the quality concept to the design function where the practices of experimental design for product design
and improvement and concurrent product/process design can develop.
• establish an over-arching quality philosophy which touches all aspects and systems within the company.
1.3 What are the four major milestone events/circumstances in the history of quality control, each of which has led
to a major step forward in the concepts, methods, and implementation of quality control?
Four major events that led to the application of modern quality principles are:
• Shewhart's introduction of a statistical measure for quality improvement at the process in the form of the control
chart.
• Deming's contributions to a new management philosophy for the institutionalization of quality improvement
across the entire organization.
• Taguchi's introduction of quality engineering, and in particular, the parameter design/robust design concept.
• the emergence of a world marketplace forcing entire nations to re-think and re-design their approach to quality.
1.4 What was the effect of division of labor on the standard of quality of goods manufactured in the United States?
Why did this occur?
The division of labor lowered quality standards in the U.S. by:
• emphasizing production over quality, i.e. emphasizing getting the numbers out.
• creating an acceptable quality level which inhibited improvement.
• taking away the worker's ownership in, and understanding and appreciation for the entire end product and its
function in the customer's hands; taking away the worker's pride in the process.
1.5 Are the use of work standards and/or wage incentives consistent with our view of quality today? Explain.
Last Updated 8/15/2006 Chapter 1 - 1
,Statistical Quality Design and Control DeVor/Chang/Sutherland
Work standards are inconsistent with today's quality view since:
• they focus on production numbers with little regard for quality.
• they place a cap on productivity by making everyone think that if the standard is being met, then the process is
operating in a satisfactory manner, that is, there is no need to look for further improvements.
• they inhibit efforts for improvement in both quality and productivity by removing incentives for making those
efforts.
1.6 What is the danger associated with the use of “acceptance sampling” for quality control? Why does the type of
attitude it promotes hinder the enhancement of competitive position?
Acceptance sampling:
• focuses on the product, instead of on improvements in the process.
• works toward containment of bad parts, rather than the prevention of the bad parts from arising in the first place.
• tends to promote the notion that there exists some "acceptable" level of defective material that we can live with,
that, in fact, is economical to strive for in a total system cost sense.
• promotes an uneconomical approach to quality by not allowing quality and productivity to improve together.
1.7 What are some possible effects realized by the general acceptance of the idea of AQL?
Acceptance of the AQL concept:
• stifles creativity by removing incentives for improvement.
• allows scrap to be accepted as part of everyday business and planning.
• motivates the belief that there exists an economic tradeoff between improved quality by the continual reduction
in defective material and the cost of doing so.
1.8 What was Shewhart’s basic approach to quality control?
Shewhart emphasized:
• economic operation of the process; the need to maintain the routine operation of the process if it is to be
economical.
• the importance of consistency of process operation; the presence of only "chance" variation sources to insure the
economic/routine operation of the process.
• the use of statistics to recognize the presence of an inconsistent process, and the removal of the root causes(s) of
variation sources to improve the economic operation of the process.
1.9 How did Shewhart's approach to quality control differ from that of Dodge and Romig?
Dodge and Romig concentrated on:
• using statistics/probability theory in a product control environment (Shewhart did so in a process control
environment).
• rejecting parts based on some acceptable quality level (Shewhart continually sought to improve the process to
improve the product).
• keeping defective product out of the customer's hands (Shewhart did so by reducing process variation to
improve the quality of the process output).
1.10 What is wrong with the phenomenon of “change of necessity"?
Change out of necessity generally results in:
• lagging behind competitors, since real change cannot happen overnight.
• lost opportunity due to the gains that would have been realized had change begun earlier.
Last Updated 8/15/2006 Chapter 1 - 2
,Statistical Quality Design and Control DeVor/Chang/Sutherland
• a reactive rather than a proactive quality philosophy.
1.11 Why has the United States over the last decade become concerned with improving quality? What forces may
be at work now that did not exist 20, 30, 40 years ago - or did they?
The U.S. has become more quality conscious in recent years because:
• a world marketplace emerged that threatened the economic success of nearly every industry.
• competitors abroad started "playing the game" under a new set of rules which included the pursuit of higher
levels of quality through the more rigorous use of quality design and improvement methods. Many of the
methods used have been available for many decades, but only recently has the global market forced companies
into use.
• companies have begun to see the broad-based benefits of the process control methodology in terms of the
enhancement of competitive position.
1.12 Who has responsibility for initiating quality control? What things need to be done?
Only management can effectively initiate and carry through on the institutionalization of a quality design and control
program. Management must:
• put quality and the never-ending pursuit of improvement on an institutional basis.
• be prepared to provide the workers with the necessary tools for successful implementation.
• lead and actively participate in the development and ongoing operation of the program, not merely support it
with words and/or budget.
1.13 Explain why it is important to consider variation about the nominal as an a measure of product/process
performance; that is, why is it not sufficient or advisable to consider only performance on average?
Today, more emphasis is being given to articulating quality in terms of variation in performance in the field during
use. Consistency of function is today recognized as an important customer-based attribute of a product. Products
that perform with small variation are considered desirable over others that have the same level of average
performance but more variability of performance about that average. Taguchi has recognized the fact that products
that function in a robust fashion, that is, have low variation about the nominal in the presence of noise/variation
inherent in the use environment, generally result in longer life and less trouble in the field during continued use.
1.14 How/why do some of the newer concepts/ways of viewing quality encourage manufacturers to reduce the
variability about the nominal in their products/processes; that is, what motivates the continual pursuit of variation
reduction?
Newer concepts of quality relate loss in quality (loss in customer utility and satisfaction) directly to the amount of
functional variation in performance during field use. This loss can directly affect the company's competitive position
from the standpoint of trouble in field use, e.g., early wearout and failure resulting in increased warranty costs, and in
terms of customer dissatisfaction resulting from inconsistent, erratic performance during use. Also, reduction in
variability is shown to directly increase the level of productivity, that is, eliminating waste and making the processes
more efficient.
1.15 A major automobile manufacturer advertises that it performs 100% inspection on all processes that produce
parts for the brake systems in its cars. They claim that the consumer can feel good about being safe in their cars.
What should the consumer feel bad about? Is there any situation in which measuring every part might be useful?
The consumer should be wary because:
• the cost of 100% inspection is most likely reflected in the car's sticker price.
Last Updated 8/15/2006 Chapter 1 - 3
, Statistical Quality Design and Control DeVor/Chang/Sutherland
• 100% inspection is not always successful in containing defects, and, most likely, the company is putting less
emphasis on attention to the processes that manufacture the brake system.
• the inspection/product control/defect containment approach to quality does not put emphasis on quality
upstream, i. e., quality by improved product and process design.
In general, the measurement of every part is unnecessary and costly. Statistically-based sampling of the product can
produce such information (if required) with a sufficient level of confidence.
1.16 The percent defective from a process that makes injection-molded plastic keychains has gradually been rising
to the point where it can no longer meet production demands in a single 8-hour shift per day. The shop floor
manager sends you a memo recommending that a second shift be added on this machine in order to get the product
out the door. As his or her boss, how would you respond to this memo?
Adding a second shift is a poor solution because:
• it does not get at the root cause of the problem to eliminate it.
• waste and inefficiency in the process and the product are actually increased as we make "more of the same," i.e.,
poor quality product.
• it is improving the S/N ratio of the process by increasing the signal, not reducing the noise, eliminating the
problem in the first place.
• it tends to promote the notion that it is the job of production to get out the numbers, and that quality is someone
else's job.
1.17 After experimenting with a certain product's performance in the field, it is found that better quality raw
materials significantly improve the product's performance in all areas. Based on these results, would you
recommend that the more expensive raw material be used for this process? Of what is this an example? How might
we better deal with this issue?
Rather than recommending the more expensive materials, future experimentation should be done to exploit any
nonlinearities in the material quality - product performance relationship, that is, pursue the development of a more
robustly performing product. This could improve output quality while using the same materials. Using a more
expensive raw material is an example of developing a more robust product by "increasing the signal", not reducing
the transmission of the environmental noise through design (Taguchi's parameter design concept).
1.18 Provide an example in your personal or professional life in which you solved a problem by:
(a) increasing the "signal,"
(b) decreasing the "noise"
in the signal-to-noise ratio you might use to characterize the performance of the process? Carefully explain your
answer.
1.19 Your boss likes the color scheme you specified for the decoration on a new motorcycle helmet, and begins
production immediately in order to have the first ones off the line in time for his son's birthday. Although you've
had no chance to consider design changes that may prove necessary, he assures you that later modifications will
cause minimal down-time on the line. Is your boss considering all the costs involved? How would you prove to him
that his decision was a poor one?
The boss is not considering costs due to:
• the poorly designed helmets that are already produced.
• the bad reputation gained from the selling of such helmets.
Experimenting with the proposed design before production starts will considerably reduce the need to redesign the
line and the harmful effects resulting from selling poorly designed helmets.
Last Updated 8/15/2006 Chapter 1 - 4
Solutions to Chapter 1 Exercises
1.1 Explain the change in the view of quality control in the United States between the decades of the 1950s, 60s,
70s, and today.
Quality control before the 1980's was characterized by:
• the need to keep bad parts from reaching the customer, mostly through the use of mass inspection techniques.
• employing the QC department as a policing function trying to catch bad product before it goes out the door.
• constant "fire-fighting", frantically trying to solve each new problem as it would arise.
• the drive to meet the acceptable standard of productivity, often typified by the work standard, and the acceptable
level of quality, often articulated in terms of an "acceptable quality level" (AQL).
From the 1980's to the present, quality control has:
• employed statistics to identify improvement opportunities in the process.
• emphasized the continual improvement in both quality and productivity.
• begun to work side-by-side with manufacturing to produce a better product and enhance the company's
competitive position.
• begun to shift away from quality as primarily a manufacturing-based concept to quality as a design-based
concept as well, i.e., pushing the quality efforts of the organization farther upstream into engineering design.
1.2 What changes must take place for the United States to become competitive again in the world marketplace?
To again become competitive in the world marketplace, the U.S. must:
• institute a process control philosophy which enables both quality and productivity to increase simultaneously.
• expand the quality concept to the design function where the practices of experimental design for product design
and improvement and concurrent product/process design can develop.
• establish an over-arching quality philosophy which touches all aspects and systems within the company.
1.3 What are the four major milestone events/circumstances in the history of quality control, each of which has led
to a major step forward in the concepts, methods, and implementation of quality control?
Four major events that led to the application of modern quality principles are:
• Shewhart's introduction of a statistical measure for quality improvement at the process in the form of the control
chart.
• Deming's contributions to a new management philosophy for the institutionalization of quality improvement
across the entire organization.
• Taguchi's introduction of quality engineering, and in particular, the parameter design/robust design concept.
• the emergence of a world marketplace forcing entire nations to re-think and re-design their approach to quality.
1.4 What was the effect of division of labor on the standard of quality of goods manufactured in the United States?
Why did this occur?
The division of labor lowered quality standards in the U.S. by:
• emphasizing production over quality, i.e. emphasizing getting the numbers out.
• creating an acceptable quality level which inhibited improvement.
• taking away the worker's ownership in, and understanding and appreciation for the entire end product and its
function in the customer's hands; taking away the worker's pride in the process.
1.5 Are the use of work standards and/or wage incentives consistent with our view of quality today? Explain.
Last Updated 8/15/2006 Chapter 1 - 1
,Statistical Quality Design and Control DeVor/Chang/Sutherland
Work standards are inconsistent with today's quality view since:
• they focus on production numbers with little regard for quality.
• they place a cap on productivity by making everyone think that if the standard is being met, then the process is
operating in a satisfactory manner, that is, there is no need to look for further improvements.
• they inhibit efforts for improvement in both quality and productivity by removing incentives for making those
efforts.
1.6 What is the danger associated with the use of “acceptance sampling” for quality control? Why does the type of
attitude it promotes hinder the enhancement of competitive position?
Acceptance sampling:
• focuses on the product, instead of on improvements in the process.
• works toward containment of bad parts, rather than the prevention of the bad parts from arising in the first place.
• tends to promote the notion that there exists some "acceptable" level of defective material that we can live with,
that, in fact, is economical to strive for in a total system cost sense.
• promotes an uneconomical approach to quality by not allowing quality and productivity to improve together.
1.7 What are some possible effects realized by the general acceptance of the idea of AQL?
Acceptance of the AQL concept:
• stifles creativity by removing incentives for improvement.
• allows scrap to be accepted as part of everyday business and planning.
• motivates the belief that there exists an economic tradeoff between improved quality by the continual reduction
in defective material and the cost of doing so.
1.8 What was Shewhart’s basic approach to quality control?
Shewhart emphasized:
• economic operation of the process; the need to maintain the routine operation of the process if it is to be
economical.
• the importance of consistency of process operation; the presence of only "chance" variation sources to insure the
economic/routine operation of the process.
• the use of statistics to recognize the presence of an inconsistent process, and the removal of the root causes(s) of
variation sources to improve the economic operation of the process.
1.9 How did Shewhart's approach to quality control differ from that of Dodge and Romig?
Dodge and Romig concentrated on:
• using statistics/probability theory in a product control environment (Shewhart did so in a process control
environment).
• rejecting parts based on some acceptable quality level (Shewhart continually sought to improve the process to
improve the product).
• keeping defective product out of the customer's hands (Shewhart did so by reducing process variation to
improve the quality of the process output).
1.10 What is wrong with the phenomenon of “change of necessity"?
Change out of necessity generally results in:
• lagging behind competitors, since real change cannot happen overnight.
• lost opportunity due to the gains that would have been realized had change begun earlier.
Last Updated 8/15/2006 Chapter 1 - 2
,Statistical Quality Design and Control DeVor/Chang/Sutherland
• a reactive rather than a proactive quality philosophy.
1.11 Why has the United States over the last decade become concerned with improving quality? What forces may
be at work now that did not exist 20, 30, 40 years ago - or did they?
The U.S. has become more quality conscious in recent years because:
• a world marketplace emerged that threatened the economic success of nearly every industry.
• competitors abroad started "playing the game" under a new set of rules which included the pursuit of higher
levels of quality through the more rigorous use of quality design and improvement methods. Many of the
methods used have been available for many decades, but only recently has the global market forced companies
into use.
• companies have begun to see the broad-based benefits of the process control methodology in terms of the
enhancement of competitive position.
1.12 Who has responsibility for initiating quality control? What things need to be done?
Only management can effectively initiate and carry through on the institutionalization of a quality design and control
program. Management must:
• put quality and the never-ending pursuit of improvement on an institutional basis.
• be prepared to provide the workers with the necessary tools for successful implementation.
• lead and actively participate in the development and ongoing operation of the program, not merely support it
with words and/or budget.
1.13 Explain why it is important to consider variation about the nominal as an a measure of product/process
performance; that is, why is it not sufficient or advisable to consider only performance on average?
Today, more emphasis is being given to articulating quality in terms of variation in performance in the field during
use. Consistency of function is today recognized as an important customer-based attribute of a product. Products
that perform with small variation are considered desirable over others that have the same level of average
performance but more variability of performance about that average. Taguchi has recognized the fact that products
that function in a robust fashion, that is, have low variation about the nominal in the presence of noise/variation
inherent in the use environment, generally result in longer life and less trouble in the field during continued use.
1.14 How/why do some of the newer concepts/ways of viewing quality encourage manufacturers to reduce the
variability about the nominal in their products/processes; that is, what motivates the continual pursuit of variation
reduction?
Newer concepts of quality relate loss in quality (loss in customer utility and satisfaction) directly to the amount of
functional variation in performance during field use. This loss can directly affect the company's competitive position
from the standpoint of trouble in field use, e.g., early wearout and failure resulting in increased warranty costs, and in
terms of customer dissatisfaction resulting from inconsistent, erratic performance during use. Also, reduction in
variability is shown to directly increase the level of productivity, that is, eliminating waste and making the processes
more efficient.
1.15 A major automobile manufacturer advertises that it performs 100% inspection on all processes that produce
parts for the brake systems in its cars. They claim that the consumer can feel good about being safe in their cars.
What should the consumer feel bad about? Is there any situation in which measuring every part might be useful?
The consumer should be wary because:
• the cost of 100% inspection is most likely reflected in the car's sticker price.
Last Updated 8/15/2006 Chapter 1 - 3
, Statistical Quality Design and Control DeVor/Chang/Sutherland
• 100% inspection is not always successful in containing defects, and, most likely, the company is putting less
emphasis on attention to the processes that manufacture the brake system.
• the inspection/product control/defect containment approach to quality does not put emphasis on quality
upstream, i. e., quality by improved product and process design.
In general, the measurement of every part is unnecessary and costly. Statistically-based sampling of the product can
produce such information (if required) with a sufficient level of confidence.
1.16 The percent defective from a process that makes injection-molded plastic keychains has gradually been rising
to the point where it can no longer meet production demands in a single 8-hour shift per day. The shop floor
manager sends you a memo recommending that a second shift be added on this machine in order to get the product
out the door. As his or her boss, how would you respond to this memo?
Adding a second shift is a poor solution because:
• it does not get at the root cause of the problem to eliminate it.
• waste and inefficiency in the process and the product are actually increased as we make "more of the same," i.e.,
poor quality product.
• it is improving the S/N ratio of the process by increasing the signal, not reducing the noise, eliminating the
problem in the first place.
• it tends to promote the notion that it is the job of production to get out the numbers, and that quality is someone
else's job.
1.17 After experimenting with a certain product's performance in the field, it is found that better quality raw
materials significantly improve the product's performance in all areas. Based on these results, would you
recommend that the more expensive raw material be used for this process? Of what is this an example? How might
we better deal with this issue?
Rather than recommending the more expensive materials, future experimentation should be done to exploit any
nonlinearities in the material quality - product performance relationship, that is, pursue the development of a more
robustly performing product. This could improve output quality while using the same materials. Using a more
expensive raw material is an example of developing a more robust product by "increasing the signal", not reducing
the transmission of the environmental noise through design (Taguchi's parameter design concept).
1.18 Provide an example in your personal or professional life in which you solved a problem by:
(a) increasing the "signal,"
(b) decreasing the "noise"
in the signal-to-noise ratio you might use to characterize the performance of the process? Carefully explain your
answer.
1.19 Your boss likes the color scheme you specified for the decoration on a new motorcycle helmet, and begins
production immediately in order to have the first ones off the line in time for his son's birthday. Although you've
had no chance to consider design changes that may prove necessary, he assures you that later modifications will
cause minimal down-time on the line. Is your boss considering all the costs involved? How would you prove to him
that his decision was a poor one?
The boss is not considering costs due to:
• the poorly designed helmets that are already produced.
• the bad reputation gained from the selling of such helmets.
Experimenting with the proposed design before production starts will considerably reduce the need to redesign the
line and the harmful effects resulting from selling poorly designed helmets.
Last Updated 8/15/2006 Chapter 1 - 4
