Deck 20: Introduction to Quality and Statistical Process Control

Question 1

A stable process is typically defined as one in which all output is operating within ± 3 standard deviations of the process center.

Answer 1

True

Question 2

A stable process is one that has had all its variation removed through quality improvement efforts on the part of the organization.

Answer 2

False

Question 3

Process control charts are used to provide signals to indicate when the output of a process is out of control.

Answer 3

True

Question 4

In process improvement efforts, the goal is to first remove the common cause variation and then to reduce the special cause variation in a system.

Question 5

It is entirely possible for the R-chart to show that a process is in statistical control and the -chart to show that the same process is out of control.

Question 6

Special cause variation is variation in the output of a process that is naturally occurring and expected and that may be the result of random causes.

Question 7

The frequency distribution of most processes' statistics will begin to resemble the shape of the normal distribution as the values are collected and grouped into classes.

Question 8

A p-chart would potentially be used to monitor the diameters of bolts made by a bolt manufacturing plant.

Question 9

The six most common sources of variation are people, machines, materials, methods, measurement, and environment.

Question 10

The control limits in the x-bar chart are set so that 95 percent of the values will fall inside the control limits when there is only common cause variation.

Question 11

If a process control chart has only one point outside the upper or lower control limits, there is insufficient evidence to conclude that the process was out of control at the time that the measurement was taken.

Question 12

One of the roles of managers who are overseeing the statistical process control analysis is to set the control limits at the desired levels prior to collecting data from the process.

Question 13

Total process variation is made up of the sum of common cause variation and special cause variation.

Question 14

The issue with a process always involves a quantitative variable.

Question 15

Control charts monitor a process as it currently operates, not necessarily how you would like it to operate.

Question 16

A process control chart can be used to determine whether the process average has shifted up or down, but is not useful for determining whether the process is just drifting in an upward or downward direction.

Question 17

We expect virtually all the data in a stable process to fall within 2 standard deviations of the mean.

Question 18

Both p-charts and c-charts are designed for use when the data we are working with are referred to as attribute data.

Question 19

Increased variation in processes and products can be detected as finer gauge measurement devices are used.

Question 20

Common cause variation is variation in the output of a process that is unexpected and has an assignable cause.

Question 21

A p-chart is useful for:

A) analyzing whether a process for a measurable variable is in or out of control.
B) analyzing processes which yield attribute data.
C) determining what the most likely cause of defects is.
D) All of the above

Question 22

Which of the following in not an out of control signal for an x-bar chart?

A) One or more points outside the control limits
B) Seven or more consecutive points that all fall on the same side of the center line
C) Six or more consecutive points moving in the same direction (an upward or downward trend)
D) Fourteen points in a row, alternating up and down

Question 23

Because variations are unavoidable in a system, the output of the system is always unpredictable.

Question 24

A plywood manufacturer is interested in monitoring the thickness of the plywood. Which of the following would be most useful for doing this?

A) p-charts
B) c-charts
C) -charts
D) Histograms

Question 25

Which of the following is not among the most common sources of variation?

A) People
B) Materials
C) Methods
D) Quotas

Question 26

A company that fills soft drinks into bottles wishes to establish an -chart to monitor the average fill level in the bottles. To do this, the company has taken a series of samples of size n = 4 bottles. The overall average fill is 12.03 ounces. The average range for the subgroups has been .06 ounces. Based on this information, what is the upper limit of the 3-sigma control limit?

A) .729
B) .0437
C) 12.09
D) 12.074

Question 27

Statistical Process Control charts are used to detect whether a process remains in control or whether it has gone out of control. Explain how the SPC signals work.

Question 28

Identify the four primary signals that indicate a change and that, if observed, will cause us to reject the null hypothesis. State the probability of a Type I error for this definition.

Question 29

The control limits in a control chart can be interpreted to mean:

A) any value falling outside the limits is a defect and the product should be discarded.
B) the range of virtually all special cause variation.
C) any value falling within the limits means the product is high quality.
D) the range of virtually all common cause variation.

Question 30

A company that fills soft drinks into bottles has established an -chart and an R-chart to monitor the average fill level in the bottles. To do this, the company has taken a series of samples of size n = 4 bottles. The overall average fill is 12.03 ounces. The average range for the subgroups has been .06 ounces. Suppose, after developing the control chart, a subgroup of size 4 yields a sample mean of 12.09 ounces and a range of .08, which of the following statements is true?

A) The process is in control on both the -chart and the R-chart.
B) The process is out of control on the R-chart but in control on the -chart.
C) The process is out of control on the -chart but in control on the R-chart.
D) The process is out of control on both the -chart and the R-chart.

Question 31

Each evening, a nationwide retail chain randomly calls 100 of the customers who came to their store that day to ask whether they were satisfied with the service they had received. The customers respond yes or no. Suppose the company has found over time that 8 percent of the customers are not satisfied ("no" answers), what is the 3-sigma upper and lower control limits for the appropriate control chart?

A) About .053 and .107
B) 0 to about .16
C) -.0.14 to about .16
D) About -1.96 to 1.96

Question 32

Referring to the SPC chart signals that a process is out of control, what type of problem does each signal indicate? List the signals.

Question 33

The x-bar chart is based on the principles of which distribution?

A) t-distribution
B) Chi square distribution
C) F distribution
D) Normal distribution

Question 34

Which of the following is the most complete group of commonly used process control charts other than the x-bar chart?

A) R-chart, c-chart
B) R-chart, p-chart, c-chart
C) p-chart, R-chart, n-chart
D) R-chart, p-chart

Question 35

The main process change that can be detected with a process control chart is:

A) the process average has shifted up or down from normal.
B) the process average is trending up or down from normal.
C) the process is behaving in such a manner that the existing variation is not random in nature.
D) All of the above

Question 36

Which of the following process changes cannot be detected with a process control chart?

A) The process average is trending up or down from normal.
B) The process average has shifted up or down from normal.
C) The process is behaving in such a manner that the existing variation is not random in nature.
D) All of the above.

Question 37

Which of the following statements is correct?

A) A process can be in statistical control, yet it can be producing defects in abundance.
B) At least three points outside the upper or lower control limits on a control chart are required before the process is deemed to be out of control.
C) If a process is out of control, then the variation that is present is limited to common cause variation.
D) When special cause variation is present, the process can be expected to be in control.

Question 38

Each evening, a nationwide retail chain randomly calls 100 of the customers who came to their store that day to ask whether they were satisfied with the service they had received. The customers respond yes or no. Suppose the company has found over time that 8 percent of the customers are not satisfied ("no" answers). If they have established a process control chart, what conclusion should be reached if the percentage of customers surveyed tonight that say no is 14 percent?

A) This result indicates that a special cause situation exists.
B) Although this point is above the upper control limit, there is no cause for alarm if this is the first time.
C) While this value is higher than "normal," it is still within the range of common cause variation and no action is needed.
D) This is outside the control limits and action should be taken

Question 39

The statistical process control (SPC) chart is one of the most important tools for identifying important issues to improve quality.

Question 40

Recently a shipping company took 30 samples, each of size n = 100, of packages that it was responsible for delivering. Out of the 3,000 total packages, 300 were delivered late. In setting up an appropriate process control chart, what would be the correct 3-sigma upper control limit value?

A) 0.03
B) 0.13
C) 0.19
D) 0.07

Question 41

Explain the relationship between control limits and specification limits.

Question 42

A major airline is interested in monitoring customer satisfaction with its baggage handling process. To do so, each day the airline randomly selects 100 customers and surveys them to determine if they are satisfied or not with the service provided. After 20 samples, a total of 260 unsatisfied customers were surveyed. a. If the airline wishes to use a control chart, which chart would you recommend and why? b. Determine the 3-sigma control limits for the appropriate control chart.