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Chapter 15 - Statistical Methods for Quality Control
Multiple Choice
1. Control charts that are based on data indicating the presence of a defect or the number of defects are called ______
control charts.
a.
attributes
b.
variables
c.
common-cause
d.
assignable-cause
2. An operating characteristic curve is based on a ________ probability distribution.
a.
normal
b.
exponential
c.
binomial
d.
uniform
3. If the value of c in a single-stage acceptance sampling plan is increased, with n remaining constant, the probability of
accepting the lot
a.
increases
b.
decreases
c.
remains the same
d.
might increase or decrease, depending on the percent defective in the lot
4. The general practice in quality control is to set the control chart’s upper and lower control limit values equal to the
variable’s mean value +/−
a.
1 standard deviation
b.
2 standard deviations
c.
2.5 standard deviations
d.
3 standard deviations
5. The sample result plotted on an np control chart is
a.
the percentage non-conforming in the sample
b.
the percentage not perfect in the sample
c.
the number of perfect units in the sample
d.
the number of defective units in the sample
6. The entire system of policies, procedures, and guidelines established by an organization to achieve and maintain quality
Chapter 15 - Statistical Methods for Quality Control
is called
a.
quality control
b.
quality engineering
c.
quality assurance
d.
quality reliance
7. Quality assurance consists of
a.
quality control
b.
quality engineering
c.
quality reliance
d.
quality control and quality engineering
8. Variations in the quality of production output that are due to factors such as machine tools wearing out are
a.
common causes
b.
assignable causes
c.
control causes
d.
None of the other answers is correct.
9. The acronym dpmo stands for
a.
defects per manual operation
b.
defects per million opportunities
c.
defects per manufacturing order
d.
defects per machine operator
10. Which of the following is a statistical method used in quality control?
a.
statistical process control
b.
acceptance sampling
c.
Both statistical process control and acceptance sampling are correct.
d.
None of the other answers is correct.
11. Normal or natural variations in the quality of production output that are due purely to chance are
a.
common causes
b.
assignable causes
c.
control causes
d.
None of the other answers is correct.
Chapter 15 - Statistical Methods for Quality Control
12. A graphical tool used to help determine whether a process is in control or out of control is a
a.
scatter diagram
b.
histogram
c.
control chart
d.
None of the other answers is correct.
13. Which of the following is not a type of a control chart?
a.
a p chart
b.
an x-bar chart
c.
an R chart
d.
All of these are types of control charts.
14. A control chart used when the output of a process is measured in terms of the mean value of a variable such as a
length, weight, temperature, and so on is
a.
a p chart
b.
an x-bar chart
c.
an R chart
d.
an np chart
15. The "Factors for and R Charts" table is intended for setting control limits how many standard deviations above and
below the center line?
a.
one
b.
two
c.
three
d.
four
16. A control chart that is used when the output of a production process is measured in terms of the proportion defective is
a.
a p chart
b.
an R chart
c.
a dp chart
d.
an np chart
17. If the calculated lower-control limit of a p chart is negative,
a.
a mistake has been made in the calculations
b.
use the absolute value of the lower limit
c.
it is set to zero
d.
None of the other answers is correct.
18. The control limits for a p chart are how many standard deviations above and below the proportion defective?
a.
one
b.
two
c.
three
d.
four
19. A control chart that is used to monitor the range of the measurements in a sample is
a.
a p chart
b.
a 6σ chart
c.
an R chart
d.
an np chart
20. A control chart that is used to monitor the number of defectives in a sample is
a.
a p chart
b.
an x-bar chart
c.
an R chart
d.
an np chart
21. The control limits for an np chart are how many standard deviations above and below the expected number of
defectives?
a.
one
b.
two
c.
three
d.
four
22. A group of items such as incoming shipments of raw material is called
a.
a sample plan
b.
an incoming control
c.
a lot
Chapter 15 - Statistical Methods for Quality Control
d.
None of the other answers is correct.
23. A statistical procedure in which the number of defective items found in a sample is used to determine whether a lot
should be accepted or rejected is called
a.
statistical process control
b.
acceptance sampling
c.
quality assurance
d.
control charts
24. In acceptance sampling, the risk of rejecting a good quality lot is known as
a.
consumer's risk
b.
producer's risk
c.
a Type II error
d.
None of the other answers is correct
25. Producer's risk is
a.
the same as the consumer's risk
b.
a Type II error
c.
a Type I error
d.
None of the other answers is correct.
26. In acceptance sampling, the risk of accepting a poor quality lot is known as
a.
consumer's risk
b.
producer's risk
c.
a Type I error
d.
None of the other answers is correct.
27. Consumer's risk is
a.
the same concept as the producer's risk
b.
a Type II error
c.
a Type I error
d.
None of the other answers is correct.
28. Accepting a good-quality lot would be a
a.
Type I error
b.
Type II error
c.
correct decision
d.
None of the other answers is correct.
29. Rejecting a poor-quality lot would be a
a.
Type I error
b.
Type II error
c.
correct decision
d.
None of the other answers is correct.
30. A graph showing the probability of accepting the lot as a function of the percent defective in the lot is
a.
a power curve
b.
a control chart
c.
an operating characteristic curve
d.
None of the other answers is correct.
31. The maximum number of defective items that can be found in the sample and still lead to acceptance of the lot is
a.
the upper control limit
b.
the lower control limit
c.
the acceptance criterion
d.
None of the other answers is correct.
32. A form of acceptance sampling in which more than one sample or stage is used is called a
a.
single-sample plan
b.
multiple-sampling plan
c.
multinomial sampling plan
d.
None of the other answers is correct.
33. Juran proposed a simple definition of quality:
a.
customer satisfaction
b.
conformance to specifications
c.
fitness for use
d.
commitment to excellence
Chapter 15 - Statistical Methods for Quality Control
34. The three quality processes on which Juran’s approach to quality focused include all of the following except
a.
quality planning
b.
quality execution
c.
quality control
d.
quality improvement
35. In contrast to Deming’s philosophy, which required a major cultural change in the organization, Juran’s programs
were designed to improve quality by
a.
working within the current organizational system
b.
reducing the number of levels in the organizational structure
c.
changing customer perception and expectations
d.
identifying and replacing the most counter-productive employees
36. The Malcolm Baldrige National Quality Award was established in
a.
1954
b.
1971
c.
1987
d.
1993
37. When a Motorola executive said “That evaluation is …. perhaps the most cost-effective, value-added business
consultation available anywhere in the world today” he was referring to
a.
ISO 9000 standards
b.
the Six Sigma philosophy
c.
Deming’s 14 Points
d.
the Malcolm Baldrige Quality Award
38. Six Sigma represents a quality level of at most ____ defects per million opportunities.
a.
3.4
b.
6.0
c.
19.7
d.
99.5
39. DFSS stands for
a.
Defects Found Sifting and Sorting
b.
Design For Six Sigma
c.
Deviation From Specifications and Standards
d.
Defer For Statistical Study
40. The second stage of a two-stage acceptance sampling plan is executed when the first-stage result is
a.
x1 > c1
b.
c1 < x1 < c2
c.
x1 > c2
d.
x1 > c1 + c2
41. If the value of c in a single-stage sampling plan is increased, with n remaining constant, the probability of accepting
the lot
a.
increases
b.
decreases
c.
is unchanged
d.
might increase or decrease, depending on the lot percent defective
42. The two general classifications of attributes in quality control are
a.
random and predictable
b.
controllable and uncontrollable
c.
variable and constant
d.
defective and nondefective
43. Control charts based on data that can be measured on a continuous scale are called
a.
normal control charts
b.
variables control charts
c.
attributes charts
d.
precision control charts
44. In practice, it is common to use the sample _____ to estimate the process _________.
a.
variances, range
b.
means, range
Chapter 15 - Statistical Methods for Quality Control
c.
standard deviations, mean
d.
ranges, standard deviation
45. Process control and acceptance sampling procedures are most closely related to
a.
linear regression procedures
b.
interval estimation procedures
c.
hypothesis testing procedures
d.
analysis of variance procedures
46. We can examine the effect of the sampling plan on both types of risks by varying the assumed
a.
percentage of defective items in the lot
b.
number of defective items in the sample
c.
probability of accepting the lot
d.
number of units in the lot
47. The process mean and standard deviation can be estimated by using samples that are selected from the process when
a.
it has only assignable-cause variation
b.
its output is uniformly distributed
c.
it is assumed to be operating in control
d.
it is operating at peak capacity
48. Heavy emphasis on statistical analysis and careful measurement are closely associated with
a.
Total Quality
b.
ISO 9000
c.
Baldrige National Quality Program
d.
Six Sigma
49. Setting the upper and lower control limits in a control chart closer to the center line results in
a.
a lower probability of a Type I error
b.
a lower probability of a Type II error
c.
lower probabilities of both Type I and Type II errors
d.
higher probabilities of both Type I and Type II errors
50. Setting the upper and lower control limits in a control chart farther from the center line results in
a.
a lower probability of a Type I error
b.
a lower probability of a Type II error
c.
lower probabilities of both Type I and Type II errors
d.
higher probabilities of both Type I and Type II errors
51. When sample results plotted on a control chart take on a pattern rather than being random, this suggests the presence
of
a.
common- cause variation
b.
assignable-cause variation
c.
either common- or assignable-cause variation
d.
neither common- nor assignable-cause variation
52. The sample result plotted on a p chart is the
a.
proportion non-defective
b.
percentage passing inspection
c.
proportion defective
d.
number of defectives
53. When only common cause variation is present in a process,
a.
no changes or adjustments are necessary
b.
we conclude the process is out of control
c.
human error is the sole source of variation
d.
the source of the variation is easily identified
54. Which of the following observed on a control chart suggests a process that is not in control?
a.
The number of points above and below the center line is about the same
b.
Points follow a smooth pattern from the lower control limit to the upper control limit
c.
Points fall randomly above and below the center line
d.
No points are outside the control limits
Subjective Short Answer
55. A soft drink filling machine is set up to fill bottles with 12 ounces of soft drink. The standard deviation s is known to
be 0.4 ounces. The quality control department periodically selects samples of 16 bottles and measures their contents.
Assume the distribution of filling volumes is normal.
Chapter 15 - Statistical Methods for Quality Control
a.
Determine the upper and lower control limits and explain what they indicate.
b.
The means of six samples were 11.8, 12.2, 11.9, 11.9, 12.1, and 11.8 ounces. Construct an x-
bar chart and indicate whether or not the process is in control.
56. A production process that is in control has a mean (μ) of 80 and a standard deviation (σ) of 10.
a.
Determine the upper and the lower control limits for sample sizes of 25.
b.
Five samples had means of 81, 84, 75, 83, and 79. Construct an x-bar chart and explain whether
or not the process is in control.
57. The upper and lower control limits of a process are 66 and 54. Samples of size 16 are used for the inspection process.
Determine the mean and the standard deviation for this process.
58. The following data represent the filling weights based on samples of 14.5 ounce cans of whole peeled tomatoes. Ten
samples of size 5 were taken. Use Excel to develop an R chart.
Sample
Observ. 1
Observ. 2
Observ. 3
Observ. 4
Observ. 5
1
14.34988
13.86116
14.62213
15.13824
15.09918
2
14.15490
13.65478
13.57654
14.01119
14.11325
3
14.33650
14.31488
15.17132
14.45736
14.40692
4
15.33073
13.69380
14.76947
14.95110
15.45946
5
13.77791
14.07638
13.73921
14.31856
14.48376
6
13.21121
15.22384
13.86012
14.17321
14.87886
7
14.84700
14.66132
14.03008
14.37953
14.56577
8
14.53612
14.91492
14.93100
14.18173
14.03840
9
15.60284
15.22188
15.15195
14.55648
14.50098
10
14.72211
14.80895
14.60674
13.98653
15.11910
