Deck 14: Quality Control

Question 1

High-cost, low-volume items often require careful inspection since we may have large costs associated with passing defectives.

Answer 1

True

Question 2

The traditional view is that the optimum level of inspection occurs when we catch at least 98.6 percent of the defects.

Answer 2

False

Question 3

Statistical process control is the measurement of rejects in the final product.

Answer 3

False

Question 4

Concluding that a process is out of control when it is not is known as a Type I error.

Question 5

If a point on a control chart falls outside one of the control limits, this suggests that the process output is nonrandom and should be investigated.

Question 6

A lower control limit must by definition be a value less than an upper control limit.

Question 7

The amount of inspection needed is governed by the costs of inspection and the expected costs of passing defective items.

Question 8

The purpose of statistical process control is to ensure that historical output is random.

Question 9

Approving the effort that occurs during the production process is known as acceptance sampling.

Question 10

Range charts and p-charts are both used for variable data.

Question 11

An R value of zero (on a range chart) means that the process must be in control since all sample values are equal.

Question 12

Attributes need to be measured, whereas variable data can be counted.

Question 13

Low-cost, high-volume items often require more intensive inspection than other types of items.

Question 14

A p-chart is used to monitor the fraction of defectives in the output of a process.

Question 15

A process that exhibits random variability would be judged to be out of control.

Question 16

Processes that are in control eliminate variations.

Question 17

An x-bar control chart can only be valid if the underlying population it measures is a normal distribution.

Question 18

The traditional view is that the optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.

Question 19

The amount of inspection we choose can range from no inspection at all to inspecting each item numerous times.

Question 20

Range charts are used mainly with attribute data.

Question 21

Tolerances represent the control limits we use on the charts.

Question 22

A run test checks a sequence of observations for randomness.

Question 23

Control limits tend to be wider for more variable processes.

Question 24

The purpose of quality control is making sure that processes are performing in an acceptable manner.

Question 25

Patterns of data on a control chart suggest that the process may have nonrandom variation.

Question 26

Approximately 99.7 percent of sample means will fall within plus or minus two standard deviations of the process mean if the process is under control.

Question 27

The output of a process may not conform to specifications even though the process may be statistically "in control."

Question 28

A c-chart is used to monitor the total number of defectives in the output of a process.

Question 29

A c-chart is used to monitor the number of defects per unit for process output.

Question 30

The primary purpose of statistical process control is to detect a defective product before it is shipped to a customer.

Question 31

The sampling distribution can be assumed to be approximately normal even when the underlying process distribution is not normally distributed.

Question 32

Statistical process control focuses on the acceptability of process output.

Question 33

The Taguchi loss function suggests that the capability ratio can be improved by extending the spread between LCL and UCL.

Question 34

Run tests are useful in helping to identify nonrandom variations in a process.

Question 35

The variation of a sampling distribution is less than the variation of the underlying process distribution.

Question 36

Process capability compares process variability to the tolerances.

Question 37

Control limits used on process control charts are specifications established by design or customers.

Question 38

Cpk can be used only when the process is centered.

Question 39

Cpk is useful even when the process is not centered.

Question 40

Run tests give managers an alternative to control charts; they are quicker and cost less.

Question 41

Attribute data are counted, variable data are measured.

Question 42

A time-ordered plot of representative sample statistics is called a(n):

A) Gantt chart.
B) simo chart.
C) control chart.
D) up-down matrix.
E) standard deviation table.

Question 43

A control chart used to monitor the fraction of defectives generated by a process is the:

A) p-chart.
B) R-chart.
C) x-bar chart.
D) c-chart.
E) Gantt chart.

Question 44

The more progressive a firm's approach to quality assurance, the less that company will need to rely on:

A) insourcing.
B) inspection.
C) outsourcing.
D) continuous improvement.
E) capability assessment.

Question 45

The greater the volume of the process being targeted for inspection, the more attractive __________ inspection is.

A) monitored
B) controlled
C) periodic
D) variable
E) automated

Question 46

Which of the following quality control sample statistics indicates a quality characteristic that is an attribute?

A) mean
B) variance
C) standard deviation
D) range
E) proportion

Question 47

Statistical process control charts are not really used to fix quality so much as they are used to:

A) highlight when processes are not capable.
B) point out when random variation is present.
C) alert when corrective action is needeD.
D) monitor the quality of incoming shipments or outgoing finished goods.
E) initiate team-building exercises.

Question 48

Inspection is a(n)_____________ activity.

A) prevention.
B) capability analysis.
C) flawless
D) corrective.
E) appraisal.

Question 49

The amount of inspection needed depends on __________ and __________.

A) the amount of automation; the reliability of inspectors
B) the quality of the supplier; the target market of the process
C) the costs of inspection; the costs of passing on defective items
D) where in the process the inspection occurs; the volume of the process
E) the cost of the item being inspected; the use of the item being inspected

Question 50

Acceptance sampling, when it is used, is used:
(I) before production.
(II) during production.
(III) after production.

A) I only
B) I and III only
C) I and II only
D) II and III only
E) I, II, and III

Question 51

When a process is not centered, its capability is measured in a slightly different way. The symbol for this case is Cpk.

Question 52

Larger samples will require wider x-bar control limits because there is more data.

Question 53

A p-chart would be used to monitor:

A) average shrinkage.
B) dispersion in sample data.
C) the fraction defectivE.
D) the number of defects per unit.
E) the range of values.

Question 54

The number of defective parts in a sample is an example of variable data because it will "vary" from one sample to another.

Question 55

Range control charts are used to monitor process central tendency.

Question 56

Control limits are based on multiples of the process standard deviation.

Question 57

A control chart used to monitor the process mean is the:

A) p-chart.
B) R-chart.
C) x-bar chart.
D) c-chart.
E) Gantt chart.

Question 58

The assurance that processes are performing in an acceptable manner is the focus of:

A) variability analysis.
B) inspection.
C) capability assessment.
D) quality control.
E) acceptance sampling.

Question 59

A c-chart is used for:

A) means.
B) ranges.
C) percent defective.
D) fraction defective per unit.
E) number of defects per unit.

Question 60

The best way to assure quality is to use extensive inspection and control charts.

Question 61

The process capability index (Cpk) may mislead if:
(I) the process is not stable.
(II) the process output is not normally distributed.
(III) the process is not centered.

A) I and II
B) I and III
C) II and III
D) II only
E) I, II, and III

Question 62

A control chart used to monitor the number of defects per unit is the:

A) p-chart.
B) R-chart.
C) x-bar chart.
D) c-chart.
E) Gantt chart.

Question 63

Which of the following relationships must always be incorrect?

A) Tolerances > process variability > control limits
B) Process variability > tolerances > control limits
C) Tolerances > control limits > process variability
D) Process variability > control limits > tolerances
E) Process variability < tolerances < control limits

Question 64

A shift in the process mean for a measured characteristic would most likely be detected by a:

A) p-chart.
B) x-bar chart.
C) c-chart.
D) R-chart.
E) s-chart.

Question 65

Which of the following is not a step in the control process?

A) Define what is to be controlled.
B) Compare measurements to a standard.
C) 100 percent inspection.
D) Take corrective action if necessary.
E) Evaluate corrective action.

Question 66

The purpose of control charts is to:

A) estimate the proportion of output that is acceptable.
B) weed out defective items.
C) determine if the output is within tolerances/specifications.
D) distinguish between random variation and assignable variation in the process.
E) provide meaningful work for quality inspectors.

Question 67

A plot below the lower control limit on the range chart:
(I) should be ignored since lower variation is desirable.
(II) may be an indication that process variation has decreased.
(III) should be investigated for assignable cause.

A) I and II
B) I and III
C) II and III
D) II only
E) I, II, and III

Question 68

A time-ordered plot of sample statistics is called a(n) ______ chart.

A) statistical
B) inspection
C) control
D) simo
E) limit

Question 69

Consider the following information:
The number of runs above and below the sample median is:

A) 3.
B) 4.
C) 5.
D) 6.
E) none of these.

Question 70

If a process is performing as it should, it is still possible to obtain observations which are outside of which limits?
(I) tolerances
(II) control limits
(III) process variability

A) I
B) II
C) I and II
D) II and III
E) I, II, and III

Question 71

The range chart (R-chart) is most likely to detect a change in:

A) proportion.
B) mean.
C) number defective.
D) variability.
E) sample size.

Question 72

A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. He knows from numerous previous samples that this service life is normally distributed with a mean of 500 hours and a standard deviation of 20 hours. On three recent production batches, he tested service life on random samples of four headlamps, with these results:
What is the sample mean service life for sample 2?

A) 460 hours
B) 495 hours
C) 500 hours
D) 515 hours
E) 525 hours

Question 73

The traditional view is that the optimum level of inspection is where the:

A) cost of inspection is minimum.
B) cost of passing defectives is minimum.
C) total cost of inspection and defectives is maximum.
D) total cost of inspection and defectives is minimum.
E) difference between inspection and defectives costs is minimum.

Question 74

A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. He knows from numerous previous samples that when this service life is in control it is normally distributed with a mean of 500 hours and a standard deviation of 20 hours. On three recent production batches, he tested service life on random samples of four headlamps, with these results:
What is the mean of the sampling distribution of sample means when the service life is in control?

A) 250 hours
B) 470 hours
C) 495 hours
D) 500 hours
E) 515 hours

Question 75

The probability of concluding that assignable variation exists when only random variation is present is:
(I) the probability of a Type I error.
(II) known as the alpha risk.
(III) highly unlikely.
(IV) the sum of probabilities in the two tails of the normal distribution.

A) I and II
B) I and IV
C) II and III
D) I, II, and IV
E) I, III, and IV

Question 76

The following data occurs chronologically from left to right:
The number of runs above and below the sample median is:

A) 2.
B) 3.
C) 4.
D) 5.
E) none of these.

Question 77

A point which is outside of the lower control limit on an R-chart:

A) is an indication that no cause of variation is present.
B) should be ignored because it signifies better-than-average quality.
C) should be investigated because an assignable cause of variation might be present.
D) should be ignored unless another point is outside that limit.
E) is impossible since the lower limit is always zero.

Question 78

The following data occurs chronologically from left to right:
The number of runs up and down is:

A) 2.
B) 3.
C) 4.
D) 5.
E) none of these.

Question 79

_______ variation is a variation whose cause can be identified.

A) Assignable
B) Controllable
C) Random
D) Statistical
E) Theoretical

Question 80

Consider the following information:
The number of runs up and down for the preceding data is:

A) 3.
B) 4.
C) 5.
D) 6.
E) none of these.