Deck 10: A: Statistical Quality Control

Question 1

Low-cost,high-volume items typically require relatively low levels of inspection.

Answer 1

False

Question 2

The variability of a process output is equivalent to the distribution of sample means of that process output for any sample size taken from the process.

Answer 2

False

Question 3

Statistical process control is based on comparing periodic samples from a process to predetermined limits.

Answer 3

True

Question 4

The part of statistical quality control that occurs during the production process is known as acceptance sampling.

Question 5

The sampling distribution of sample means taken from a process has less variability than the distribution of the process.

Question 6

Variation in a sample statistic collected from a process may be either random variation or assignable variation.

Question 7

Typically the production of high-cost,low-volume items require little quality control inspection.

Question 8

The optimum level of inspection occurs when the cost of passing defectives is minimized.

Question 9

Approximately 99.7% of sample means will fall within ± two standard deviations of the process mean.

Question 10

Even when the sample size is fairly small,the sampling distribution can be assumed to be approximately normal even if the underlying process distribution is not normally distributed.

Question 11

The primary purpose of statistical process control is to detect defects in finished products before they are shipped to customers.

Question 12

The main task in process control is to distinguish assignable from random variation.

Question 13

Quality control efforts that occur during production are referred to as statistical process control.

Question 14

The frequency and quantity of inspection depends primarily on the cost of inspection.

Question 15

Assignable variation is variation due to a specific cause,such as tool wear.

Question 16

The end of a manufacturing process is always the best place for a quality inspection point.

Question 17

Control limits distinguish between non-random and assignable variability.

Question 18

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

Question 19

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

Question 20

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

Question 21

Design specifications are equivalent to control limits.

Question 22

Concluding that a process has changed when it has not is known as a Type II error.

Question 23

If a point on a control chart falls outside one of the control limits,this suggests that the process output is non-random,assignable variation.

Question 24

The sample size chosen for control charts depends on the cost of inspection versus the expected cost of Type II error.

Question 25

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

Question 26

Sample range control charts are used to measure shifts in the process mean.

Question 27

Control limits are specifications established by engineering design or customer requirements.

Question 28

Control charts based on attribute data are for process characteristics that are counted rather than measured.

Question 29

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

Question 30

A p-chart is used to measure shifts in process dispersion.

Question 31

Concluding that a process has not changed when it has is known as a Type I error.

Question 32

Attributes are process characteristics that must be measured rather than counted.

Question 33

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

Question 34

The probability of a Type I error is the probability of concluding that assignable variation is present even though only random variation exists.

Question 35

A sample statistic that falls outside the control limits suggests that the process mean has changed.

Question 36

Concluding that a process has changed when it has not is known as a Type I error.

Question 37

Sample range control charts are used to monitor process dispersion.

Question 38

The number of defective parts in a sample is a process characteristic that is counted rather than measured.

Question 39

A sample statistic that falls inside the control limits suggests there is assignable variation in the process.

Question 40

Control limits are determined based on design specification limits.

Question 41

In order for a process to be capable,it must have a capability ratio of at least 1.00.

Question 42

There is no direct link between design specifications and statistical process control limits.

Question 43

A process is "capable" if the process output falls within the design specification.

Question 44

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

Question 45

The process capability index,indicated by Cpis calculated as the ratio of the design specification width to the process width.

Question 46

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 47

Process variability is a key factor in process capability.

Question 48

The probability of concluding that an 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 distribution.

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

Question 49

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

A) Define the quality characteristic to be controlled.
B) Determine a quality control point in the process.
C) Eliminate all defects found.
D) Plan how inspection is to be done.
E) All of the choices are steps.

Question 50

The term "2 sigma limits" in the context of a control chart refers to the variability of the:

A) process.
B) population.
C) sample.
D) sampling distribution.
E) none of the choices are correct.

Question 51

When a process is not centred,its capability should be based on C_pk because it considers the upper and lower design specifications separately and not just the overall design specification width.

Question 52

A process capability index (C_p)of 0.70 indicates that a process is capable of producing to design specifications.

Question 53

The process capability index,indicated by Cpkis used only when the process is centred.

Question 54

Using three sigma control limits (rather than two sigma limits)tends to have what impact on error probabilities?

A) Increase the Type II and decrease the Type I.
B) Decrease the Type II and increase the Type I.
C) Decrease the Type I and Type II.
D) Increase the Type I and Type II.
E) Have little or no impact.

Question 55

"Process capability" compares "process variability" to the "design specifications".

Question 56

Control limits and process variability are directly related.

Question 57

The optimum level of inspection for quality control is where the:

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

Question 58

The purpose of control charts is to:

A) estimate the proportion of output that is acceptable.
B) inspect the quality of all outputs from a process.
C) determine if the output of a process is within specifications.
D) distinguish between random variation and assignable variation in a process.
E) all of these choices are correct.

Question 59

Six sigma quality refers to achieving process variation so small that the half-width of the design specification equals six times the standard deviation of the process.

Question 60

Control limits are statistical limits that reflect the extent to which sample statistics such as means and ranges can vary due to random variation alone.

Question 61

A point that plots below the lower control limit on the range chart:
I)should be ignored because 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 62

What is the sample mean service life for sample 2?

A) 470 hours
B) 495 hours
C) 500 hours
D) 515 hours
E) 525 hours

Question 63

What is the sample mean package weight for Thursday?

A) 19 ounces
B) 20 ounces
C) 20.6 ounces
D) 21 ounces
E) 23 ounces

Question 64

If he uses upper and lower control limits of 520 and 480 hours,on what sample(s)(if any)does service life appear to be out of control?

A) Sample 1
B) Sample 2
C) Sample 3
D) Both samples 2 and 3.
E) None of the choices are correct.

Question 65

The DMAIC methodology involves all EXCEPT which of the following?

A) Define
B) Model
C) Analyze
D) Improve
E) Control

Question 66

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

A) is an indication that no process variation is present.
B) should be ignored because it signifies very low process variation.
C) should be investigated because it could indicate improvements in the methods used in a process.
D) should be ignored unless another point is outside that limit.
E) is impossible because the lower limit is always zero.

Question 67

Which statement is an accurate description of a process that is "capable"?

A) No random variation is evident, only assignable variation.
B) Process variability is greater than variation allowed by design specifications.
C) Process variability is less than variation allowed by design specifications.
D) Assignable variation is less than random variation.
E) Assignable variation is greater than random variation.

Question 68

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 69

For which of the following would a p-chart be used?

A) Monitor the process means for samples.
B) Monitor dispersion in sample data.
C) Monitor the proportion of defectives in a sample.
D) Monitor the number of defects per unit.
E) Monitor the range of values in samples.

Question 70

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

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

Question 71

What is the standard deviation of the sampling distribution of sample means?

A) 5 hours
B) 6.67 hours
C) 10 hours
D) 11.55 hours
E) 20 hours

Question 72

Studies on a bottle-filling machine indicates it fills bottles to a mean of 16 ounces with a standard deviation of 0.10 ounces.Assuming the Cpindex = 1.0,what is/are the process specification(s)?

A) 0.10 ounces.
B) 0.60 ounces.
C) 16.0 ounces plus or minus 0.60 ounces.
D) 16.0 ounces plus or minus 0.30 ounces.
E) None of the choices are correct.

Question 73

The six sigma quality improvement methodology is called:

A) PDSA
B) DMAIC
C) 5W2H
D) continuous improvement system.
E) none of the choices are correct.

Question 74

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 75

If he uses upper and lower control limits of 520 and 480 hours,what is his risk (alpha)of concluding service life is out of control when it is actually under control (Type I error)?

A) 0.0026
B) 0.0456
C) 0.3174
D) 0.6826
E) 0.9544

Question 76

Which of the following is not needed to calculate sample mean control charts?

A) A choice for z, the standard normal deviate (usually 2 or 3).
B) The standard deviation of the sampling distribution.
C) The sample range.
D) The average of sample means (grand mean).

Question 77

What value should be used as the mean of the sampling distribution of sample means?

A) 470 hours
B) 495 hours
C) 500 hours
D) 515 hours
E) 525 hours

Question 78

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 79

Which of the following quality control sample statistics measures a quality characteristic which is an attribute?

A) Mean
B) Variance
C) Standard deviation
D) Range
E) Proportion

Question 80

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

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