Deck 15: Statistical 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

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

Answer 2

False

Question 3

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

Answer 3

False

Question 4

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

Question 5

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

Question 6

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

Question 7

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

Question 8

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

Question 9

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.

Question 10

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

Question 11

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

Question 12

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

Question 13

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

Question 14

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

Question 15

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

Question 16

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

Question 17

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

Question 18

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

Question 19

Control limits distinguish between non-random and assignable variability.

Question 20

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 21

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

Question 22

Sample range control charts are used to monitor process dispersion.

Question 23

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

Question 24

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

Question 25

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

Question 26

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

Question 27

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

Question 28

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

Question 29

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

Question 30

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 31

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

Question 32

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

Question 33

Control limits are determined based on design specification limits.

Question 34

Design specifications are equivalent to control limits.

Question 35

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

Question 36

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

Question 37

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

Question 38

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

Question 39

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

Question 40

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

Question 41

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.

Question 42

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

Question 43

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

Question 44

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 45

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 46

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

Question 47

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

Question 48

Appraisal of a good or service against a standard is called inspection.

Question 49

Design of experiments involves performing experiments to determine the best control limits for a process.

Question 50

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)Plan corrective action

Question 51

Control limits and process variability are directly related.

Question 52

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 53

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

Question 54

As a rule of thumb,operations with a high proportion of human involvement necessitate less inspection than mechanical operations,which tend to be less reliable.

Question 55

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 56

Process variability is a key factor in process capability.

Question 57

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

Question 58

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

Question 59

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

Question 60

As the sample size increases,the distribution of sample averages approaches a Normal distribution regardless of the shape of the sampled population.This is identified in which of the following?

A)Assignable variation
B)Random variation
C)Central limit theorem
D)Type I errors
E)Mean charts

Question 61

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 62

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.

Question 63

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 64

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.

Question 65

The six sigma quality improvement methodology is called:

A)PDSA
B)DMAIC
C)5W2H
D)continuous improvement system.

Question 66

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 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

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 69

A point that plots below the lower control limit on the range chart:

A)should be ignored because lower variation is desirable.
B)should be investigated for random variation.
C)may be an indication that process variation has decreased
D)is not possible
E)is due to a shift in the process mean

Question 70

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 71

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 72

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 73

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 74

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.

Question 75

When using control charts sample size is important.Smaller samples are more likely to reveal a process change because a change is more likely to take place ______ the large sample,rather than ________ small samples.

A)outside,outside
B)outside,inside
C)exclusive to,inside,
D)between,outside
E)within,between

Question 76

The DMAIC methodology involves all EXCEPT which of the following?

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

Question 77

The probability of concluding that an assignable variation exists when only random variation is present is:

A)Statistical shift
B)Specification variation
C)Control limit error
D)Type I error
E)Type II error

Question 78

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 79

When a process is judged out of control for an important character?istic,what corrective action should be taken?

A)The process should be stopped and corrective action must be taken.
B)The process should be investigated for Type I error.
C)The process should be investigated for Type II error.
D)The process should continue,however,100% inspection is required.
E)The process should continue until another sample is taken.

Question 80

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