Deck 10: Quality Control

Question 1

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

Answer 1

True

Question 2

Processes that are in control eliminate variations.

Answer 2

False

Question 3

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

Answer 3

True

Question 4

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

Question 5

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

Question 6

Range charts are used mainly with attribute data.

Question 7

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

Question 8

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

Question 9

The optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.

Question 10

High-cost, low-volume items often require careful inspection since we make them so infrequently.

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

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

Question 13

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

Question 14

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

Question 15

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

Question 16

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

Question 17

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 18

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

Question 19

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

Question 20

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

Question 21

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

Question 22

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

Question 23

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

Question 24

Quality control is making sure that processes are performing in an acceptable manner.

Question 25

C_pk is useful even when the process is not centered.

Question 26

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

Question 27

A run test checks a sequence of observations for randomness.

Question 28

Process capability compares process variability to the tolerances.

Question 29

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

Question 30

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

Question 31

Tolerances represent the control limits we use on the charts.

Question 32

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

Question 33

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

Question 34

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 35

The process capability index (indicated by C_pk) can be used only when the process is centered.

Question 36

Control limits tend to be wider for more variable processes.

Question 37

Statistical process control focuses on the acceptability of process output.

Question 38

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

Question 39

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

Question 40

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

Question 41

Range control charts are used to monitor process central tendency.

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

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 44

Attribute data are counted, variable data are measured.

Question 45

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 46

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 47

Quality control tools 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

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

Question 49

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

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

Question 50

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

Question 51

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

Question 52

The more effective and all-encompassing a firm's quality control and continuous improvement efforts, the less that company will need to rely on:

A) insourcing.
B) inspection.
C) outsourcing.
D) acceptance sampling.
E) capability assessment.

Question 53

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

Question 54

Quality control, in contrast to quality assurance, is implemented:

A) during production.
B) by top management.
C) after production.
D) by self-directed teams.
E) before inspection.

Question 55

Inspection is a(n):

A) prevention.
B) control.
C) monitoring.
D) corrective.
E) appraisal.

Question 56

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 57

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

Question 58

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 59

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 60

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 61

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 62

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 63

The following data occurs chronologically from left to right: $$\begin{array} { l l l l l l } 15.2 & 19.7 & 16.0 & 11.1 & 14.8 & 14.5\end{array}$$ The number of runs up and down is:

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

Question 64

The following data occurs chronologically from left to right: $$\begin{array} { l l l l l l } 15.2 & 19.7 & 16.0 & 11.1 & 14.8 & 14.5\end{array}$$ The number of runs with respect to the sample median is:

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

Question 65

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 66

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 67

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 68

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 69

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 70

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: $$\begin{array} { r } { \text { Service Life (hours) } }\\\begin{array} { l l l l l } \text { Sample } & \\\hline 1 & 495 & 500 & 505 & 500 \\2 & 525 & 515 & 505 & 515 \\3 & 470 & 480 & 460 & 470\end{array}\end{array}$$ 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 71

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 72

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

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

Question 73

The process capability index (C_pk) 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 74

Consider the following information: $$\begin{array} { l r r r r r r } \text { Observations } & 1 & 2 & 3 & 4 & 5 & 6 \\\hline \text { Num. of defects } & 10 & 18 & 13 & 15 & 9 & 12\end{array}$$ The number of runs up and down for the preceding data is:

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

Question 75

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

A) Define what is to be controlled.
B) Compare measurements to a standard.
C) Eliminate each of the defects as they are identified.
D) Take corrective action if necessary.
E) Evaluate corrective action.

Question 76

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 77

_______ variation is a variation whose cause can be identified.

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

Question 78

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 79

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 80

Consider the following information: $$\begin{array} { l r r r r r r } \text { Observations } & 1 & 2 & 3 & 4 & 5 & 6 \\\hline \text { Num. of defects } & 10 & 18 & 13 & 15 & 9 & 12\end{array}$$ The number of runs with respect to the sample median is:

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