Deck 13: Statistical Quality Control

Question 1

An example of assignable variation in a production system may be that workers are not identically trained.

Answer 1

True

Question 2

To obtain a 99.7 percent confidence level in a p-chart, we would use a value of 3 for "z."

Answer 2

True

Question 3

Measurement by attributes means taking a sample, measuring the attribute in question, and determining the level of quality in the population from which the sample was drawn.

Answer 3

False

Question 4

Genichi Taguchi's view of the cost of quality is that variance is a discontinuous function.

Question 5

Process control is concerned with monitoring quality after the product or service has been produced.

Question 6

Acceptance sampling is performed on goods that already exist to determine what percentage of items conforms to specifications.

Question 7

Statistical process control involves testing random samples of output from a process to determine whether the process is producing items within a preselected range.

Question 8

It is impossible to have zero variability in production processes.

Question 9

The value for "z" used in quality control charts is based on the degree of confidence you want to have in the resulting UCL and LCL values.

Question 10

Attributes are those quality characteristics that are classified as either conforming or not conforming to specification.

Question 11

A p-chart has upper and lower control limits expressed as lines on the chart. As long as the sample values fall between these two lines, there is no need to investigate process behavior.

Question 12

In acceptance sampling, the value for the acceptance number (c) is determined by the interaction of the acceptable quality level (AQL), the lot tolerance percent defective (LTPD), the probability of rejecting a high-quality lot (alpha), and the probability of accepting a low-quality lot (beta).

Question 13

In acceptance sampling, the number of units in the sample (n) is determined by the interaction of the acceptable quality level (AQL), the lot tolerance percent defective (LTPD), the probability of rejecting a high-quality lot (alpha), and the probability of accepting a low-quality lot (beta).

Question 14

If the fraction defective is 0.12 based on a sample size of 16, the standard deviation used in the p-chart is about 0.08.

Question 15

The p-chart is only useful for sampling that deals with continuous variables.

Question 16

The capability index is used to gauge economic changes in service systems.

Question 17

Variation that is inherent in a production process itself is called assignable variation.

Question 18

Variation that is inherent in a production process itself is called common variation.

Question 19

An example of assignable variation in a production system may be that a machine is not adjusted properly.

Question 20

If the fraction defective is 0.4 based on a sample size of 100, the standard deviation used in the p-chart is about 0.10.

Question 21

LTPD in acceptance sampling stands for lot tolerance for parts defective.

Question 22

For R-charts, the typical sample size is 10-15.

Question 23

The probability associated with rejecting a high-quality lot is denoted in acceptance sampling with the Greek letter alpha.

Question 24

In monitoring process quality, we might use which of the following statistics?

A) Absolute values
B) Percentage deviation from tolerance centers
C) "k" values for the sample mean
D) Logarithmic control intervals
E) Difference between the highest and lowest value in a sample

Question 25

The capability index (Cpk) calculates the percentage of items being produced within specifications.

Question 26

The capability index (Cpk) indicates the position of the mean and tails of a process's variance relative to design specifications.

Question 27

You have just used the capability index (Cpk) formulas to compute the two values "min [1.5, 1]." Which of the following is the proper interpretation of these numbers?

A) The true capability index value is 1.
B) The mean of the production process has shifted to the left of the design limits.
C) The mean of the production process has shifted to the right of the design limits.
D) The mean has not shifted at all.
E) The true capability index value is between 1.5 and 1.

Question 28

The Greek letter alpha is associated with consumer's risk.

Question 29

You have just used the capability index (Cpk) formulas to compute the two values "min [2, 2.5]." Which of the following is the proper interpretation of these numbers?

A) The true capability index value is 2.5.
B) The mean of the production process has shifted to the left of the design limits.
C) The mean of the production process has shifted to the right of the design limits.
D) The mean has not shifted at all.
E) The true capability index value is between 2 and 2.5.

Question 30

In sampling variables, the actual measurements of the variable observed are used regardless of whether the unit is good or bad.

Question 31

The producer's risk associated with rejecting a high-quality lot is denoted in acceptance sampling with the Greek letter beta.

Question 32

Sampling plans are generally displayed graphically through the use of operating characteristic (OC) curves.

Question 33

Total, 100 percent inspection can never be cost justified.

Question 34

You have just used the capability index (Cpk) formulas to compute the two values "min [1, 1]." Which of the following is the proper interpretation of these numbers?

A) The true capability index value is exactly 1.
B) The mean of the production process has shifted to the left of the design limits.
C) The mean of the production process has shifted to the right of the design limits.
D) The mean has not shifted at all.
E) None of these choices are correct.

Question 35

Designers establish specifications that solely define the target value only.

Question 36

One hundred percent inspection is justified when the cost of inspection is low.

Question 37

Standard practice in statistical process control for variables is to set control limits so that 95 percent of the sample means will fall within the UCL and the LCL.

Question 38

AQL stands for accepting questionable lots in production quality management.

Question 39

The probability associated with accepting a low-quality lot is denoted in acceptance sampling with the Greek letter alpha.

Question 40

A rule of thumb for p-charts is to use a sample size of at least 250.

Question 41

You want to determine the control lines for a p-chart for quality control purposes. If the total number of defects from all samples is 560, the number of samples is 70, and the sample size is 80, which of the following would be the standard deviation used in developing the control lines?

A) 0.9000
B) 0.4556
C) 0.0335
D) 0.0011
E) 0.0112

Question 42

You want to determine the control lines for a p-chart for quality control purposes. If the total number of defects from all samples is 2,500, the number of samples is 100, and the sample size is 500, which of the following would be the standard deviation used in developing the control lines?

A) 0.4900
B) 0.2499
C) 0.0707
D) 0.000315
E) 0.000975

Question 43

If there are 12 total defects from 10 samples, each sample consisting of 100 individual items in a production process, which of the following is the fraction defective that can be used in a p-chart for quality control purposes?

A) 12
B) 1.2
C) 0.12
D) 0.012
E) 0.0012

Question 44

You want to develop a three-sigma R-chart. You know the average range is 5 based on several samples of size 10. Which of the following is the resulting UCL?

A) 20.9
B) 8.9
C) 7.02
D) 5
E) 3.1

Question 45

You are going to develop an R-chart based on range statistics, and you are using a sample size of 9 for your charting purposes. Which of the following is the lower control limit D₃ factor for the chart?

A) 0.08
B) 0.14
C) 0.18
D) 0.22
E) 0.29

Question 46

You are going to develop an X-bar chart based on range statistics, and you are using a sample size of 12 for your charting purposes. Which of the following is the A₂ factor for the X-bar chart?

A) 0.37
B) 0.31
C) 0.27
D) 0.22
E) 0.18

Question 47

Quality control charts usually have a central line and upper and lower control limit lines. Which of the following is a reason that the process being monitored with the chart should be investigated?

A) A single point falls above or below the control limits.
B) Behavior is normal.
C) A large number of plots are on or near the central line.
D) There is no real trend in any direction.
E) There is a change in raw materials or operators.

Question 48

Quality control charts usually have a central line and upper and lower control limit lines. Which of the following is not a reason that the process being monitored with the chart should be investigated?

A) A large number of plots are close to the upper or lower control lines.
B) The behavior of the plots is erratic.
C) A single point falls above or below the control limits.
D) There is a change in raw materials or operators.
E) There is a run of five above the central line.

Question 49

For which of the following should we use an R-chart to monitor process quality?

A) Grades in a freshman "pass/fail" course
B) Tire pressures in an auto assembly plant
C) Vehicles passing emissions inspection
D) Computer software errors
E) Number of units with missing operations

Question 50

For which of the following should we use an R-chart to monitor process quality?

A) Weighing trucks at a highway inspection station to determine if they are overloaded
B) Deciding whether an airliner has sufficient fuel for its trip
C) Student grades measured from 1 to 100
D) Determining whether vehicles from a motor pool will run
E) Determining the accuracy of a forecast of "snow"

Question 51

You are developing an X-bar chart based on sample means. You know the standard deviation of the sample means is 4, the desired confidence level is 99 percent, and the average of the sample means is 20. Which of the following is your LCL?

A) 36
B) 24
C) 9.68
D) 16.79
E) 30.32

Question 52

You want to determine the upper control line for a p-chart for quality control purposes. You take several samples of a size of 100 items in your production process. From the samples, you determine the fraction defective is 0.05 and the standard deviation is 0.01. If the desired confidence level is 99.7 percent, which of the following is the resulting UCL value for the line?

A) 0.39
B) 0.08
C) 0.06
D) 0.05
E) None of these choices are correct.

Question 53

You want to develop a three-sigma R-chart. You know the average range is 12 based on several samples of size 6. Which of the following is the resulting LCL?

A) 20.0
B) 18.3
C) 7.02
D) 5.6
E) 0.0

Question 54

For which of the following should we use a p-chart to monitor process quality?

A) The dimensions of brick entering a kiln
B) Lengths of boards cut in a mill
C) The weight of fluid in a container
D) Grades in a freshman "pass/fail" course
E) Temperatures in a classroom

Question 55

For which of the following should we use a p-chart to monitor process quality?

A) Defective electrical switches
B) Errors in the length of a pencil
C) Weight errors in cans of soup
D) Temperature of entrees in a restaurant
E) Letter grades on a final examination

Question 56

You are developing an X-bar chart based on sample means. You know the standard deviation of the sample means is 4, the desired confidence level is 99.7 percent, and the average of the sample means is 24. Which of the following is your UCL?

A) 36
B) 24
C) 12
D) 4
E) None of these choices are correct.

Question 57

If there are 40 total defects from 8 samples, each sample consisting of 200 individual items in a production process, which of the following is the fraction defective that can be used in a p-chart for quality control purposes?

A) 2.5
B) 0.25
C) 0.025
D) 0.0025
E) 0.00025

Question 58

You want to determine the control lines for a p-chart for quality control purposes. If the desired confidence level is 99 percent, which of the following values for "z" would you use in computing the UCL and LCL?

A) 0.99
B) 2
C) 2.58
D) 3
E) None of these choices are correct.

Question 59

You want to determine the lower control line for a p-chart for quality control purposes. You take several samples of a size of 50 items in your production process. From the samples, you determine the fraction defective is 0.006 and the standard deviation is 0.001. If the desired confidence level is 99.7 percent, which of the following is the resulting LCL value for the line?

A) 0.0
B) 0.002
C) 0.003
D) 0.004
E) None of these choices are correct.

Question 60

For which of the following should we use an X-bar chart based on sample means to monitor process quality?

A) Grades in a freshman "pass/fail" course
B) Tire pressures in an auto assembly plant
C) Vehicles passing emissions inspection
D) Computer software errors
E) Number of units with missing operations

Question 61

Consider a sampling plan with n = 40 and c = 1 and given Acceptable quality level (AQL), Lot tolerance percent defective (LTPD), producer's risk (α) and consumer's risk (β). Suppose that c is increased to 2, keeping AQL and LTPD unchanged, consumer's risk (β) will

A) Always decrease
B) Always increase
C) Sometime decrease
D) Stay the same
E) None of these choices are correct.

Question 62

Other things remaining the same, and assuming thatis smaller than USL and larger than LSL, if the standard deviation (σ) of the process decreases, process capability index (Cpk) of the process will
I. Stay the same
II. Will always increase
III. Will always decrease
IV. Will sometimes increase

A) I
B) II
C) III
D) Either II or III
E) IV

Question 63

You are going to develop an R-chart based on range statistics, and you are using a sample size of 15 for your charting purposes. Which of the following is the upper control limit D₄ factor for the chart?

A) 1.65
B) 1.70
C) 1.76
D) 1.87
E) 1.92

Question 64

Consider a sampling plan with n = 40 and c = 1 and given Acceptable quality level (AQL), Lot tolerance percent defective (LTPD), producer's risk (α) and consumer's risk (β). Suppose that c is increased to 2, keeping AQL and LTPD unchanged, producer's risk (α) will

A) Always decrease
B) Always increase
C) Sometime decrease
D) Stay the same
E) None of these choices are correct.