Deck 10: Quality Control

Question 1

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

Answer 1

False

Question 2

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

Answer 2

False

Question 3

Processes that are in control eliminate variations.

Answer 3

False

Question 4

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

Question 5

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

Question 6

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

Question 7

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

Question 8

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

Question 9

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

Question 10

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

Question 11

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

Question 12

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

Question 13

Statistical Process Control is the measurement of rejects in the final product.

Question 14

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

Question 15

Range charts are used mainly with attribute data.

Question 16

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

Question 17

Low-cost, high-volume items often require more intensive inspection.

Question 18

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

Question 19

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

Question 20

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

Question 21

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

Question 22

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

Question 23

"Process capability" compares "process variability" to the "tolerances."

Question 24

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

Question 25

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

Question 26

Statistical process control focuses on the acceptability of process output.

Question 27

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

Question 28

Tolerances represent the control limits we use on the charts.

Question 29

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

Question 30

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

Question 31

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

Question 32

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

Question 33

Control limits tend to be wider for more variable processes.

Question 34

Even if the process is not centered, the process capability index (indicated by Cpk) is very useful.

Question 35

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

Question 36

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

Question 37

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

Question 38

Patterns of data on a control chart suggest that the process may have non-random variation.

Question 39

A run test checks a sequence of observations for randomness.

Question 40

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

Question 41

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

Question 42

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 43

Type I and Type II errors refer to the magnitude of variation from the standard.

Question 44

Range control charts are used to monitor process central tendency.

Question 45

The larger the process variation, the tighter the specifications should be.

Question 46

An "up and down" run test uses the median as a reference point and measures the percentage above and below the median.

Question 47

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

Question 48

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 49

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 50

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

A)Gantt chart
B)SIMO-chart
C)Control Chart
D)Up-Down Matrix
E)Standard deviation table

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

"Quality of conformance" is concerned with whether a product or service conforms to its specifications.

Question 53

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

Question 54

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 55

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

Question 56

Non-random variation is likely whenever all observations are between the LCL and UCL.

Question 57

Attribute data are counted, variable data are measured.

Question 58

The greater the capability ratio, the higher the rejects.

Question 59

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

Question 60

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

Question 61

Four samples of three observations each have been taken, with actual measurements (in centimeters) shown below.Construct three-sigma mean and range charts.

Question 62

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 63

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 64

Perform run tests on the given data.What can you conclude?

Question 65

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 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

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 68

A process that makes chocolate candy bars has an output that is normally distributed with a mean of 6 oz.and a standard deviation of .01 oz.A job is to be run that requires 200 candy bars.
Determine three sigma control limits for an x-bar chart assuming a sample size of 10.
If specifications are 5.98 to 6.02, what run size should be used for this job so that the expected number of good candy bars is 200, assuming the process is in control?

Question 69

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 70

A town's department of public works is concerned about adverse public reaction to a sewer project that is currently in progress.Because of this, the Commissioner of Public Works has authorized a weekly survey to be conducted of town residents.Each week, a sample of 100 residents is questioned on their feelings towards the project.The results to date are shown below.Analyze this data using control charts that would provide for a 5% risk of Type I error.

Question 71

Construct the appropriate two-sigma control chart for the sample observations listed below.

Question 72

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 73

_______ variation is a variation whose cause can be identified.

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

Question 74

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

Question 75

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 76

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

A)Statistical
B)Inspection
C)Control
D)SIMO
E)Limit

Question 77

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 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

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

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

Question 80

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