Deck 8: Measuring and Controlling Quality

Question 1

A "hugging the center line" pattern in a control chart can be the result of taking each sample from different process but not mixed together.

Answer 1

False

Question 2

Histograms allow you to distinguish between common and special causes of variation.

Answer 2

False

Question 3

The frequency of sampling in pre-control is often determined by dividing the time period between two successive out-of-control signals by six.

Answer 3

True

Question 4

If all sample averages on an
-chart fall within the control limits,all output will be conforming.

Question 5

A histogram of data that resembles the normal distribution indicates that the process is in control.

Question 6

A p-chart is used with the attribute data.

Question 7

The larger the sample size,the narrower the control limits.

Question 8

Common and special causes of variation must be eliminated before process capability can be determined.

Question 9

For variable data,the two important quality measures are the proportion nonconforming and nonconformances per unit.

Question 10

The total observed variation in production output is the sum of the true process variation plus variation due to measurement.

Question 11

Pre-control should only be used when process capability is greater than 88 percent of the tolerance.

Question 12

Process capability indices cannot be computed from data in an
-chart.

Question 13

Attribute measurement requires a much larger sample size than variable measurement to obtain the same amount of statistical information.

Question 14

A measurement system may be precise but not necessarily accurate at the same time.

Question 15

If most of the points on a control chart are within the control limits with a recognizable pattern,then the process is in statistical control.

Question 16

Rolled throughput yield is the proportion of conforming units that results from a series of process steps.

Question 17

A nonconforming unit of work is one that has no defects or errors.

Question 18

If points on a control chart are determined to be the result of special causes,the points should be eliminated and new control limits should be computed.

Question 19

The center line for the np-chart is the average number of nonconforming items per sample.

Question 20

A better alternative to the
-chart to monitor variation is to compute and plot the standard deviation s of each sample.

Question 21

A c-chart is based on the binomial distribution.

Question 22

When constructing a u-chart,the standard deviation of each sample varies because the size of the sampling unit varies.

Question 23

A(n) _____ characterizes the presence or absence of nonconformances in a unit of work.

A)variable
B)indicator
C)attribute
D)error

Question 24

In pre-control,which zone covers the nominal specification of a process?

A)Gray zone
B)Yellow zone
C)Red zone
D)Green zone

Question 25

Control limits for the s-chart are given by: LCL_s = B₃s and UCL_s = B₄s,where B₃ and B₄ are constants.

Question 26

Compared to variable measurement,attributes measurement requires _____ to obtain the same amount of statistical information about the quality of the product.

A)a more distributed population
B)more nonconformances
C)a larger sample
D)a smaller sample

Question 27

_____ is a study of variation in a measurement system using statistical analysis.

A)Metrology study
B)SPC study
C)Calibration study
D)A repeatability and reproducibility (R&R) study

Question 28

The output of a process is stable and normally distributed.If the process mean equals 23.5,the percentage of output expected to be less than or equal to the mean:

A)is less than 25% .
B)is 50%.
C)is greater than 75%.
D)cannot be determined without knowing the standard deviation value.

Question 29

If a process is neither capable nor in control,the appropriate first step is to:

A)remove common causes of variation.
B)redesign the equipment.
C)remove special causes of variation.
D)determine the process capability index.

Question 30

If the variation in the process is due to common causes alone,the process is said to be:

A)out of control.
B)in statistical control.
C)in pre-control.
D)out of capability.

Question 31

A process is said to be out of control when:

A)common causes are present.
B)special causes are present.
C)the process is not capable of meeting specifications.
D)the upper and lower control limits cannot be computed.

Question 32

Control limits for variables and attributes data utilize the same mathematical formulas.

Question 33

Process capability calculations make little sense if the process:

A)data were taken over a period of time.
B)is not in statistical control.
C)variations are due to common causes.
D)is not initiated.

Question 34

In determining the method of sampling,samples should be chosen to be as heterogeneous as possible so that each sample reflects the system of common causes or assignable causes that may be present at that point in time.

Question 35

_____ is measured as the amount of error in a measurement in proportion to the total size of the measurement.

A)Precision
B)Accuracy
C)Systematic bias
D)Capability

Question 36

Defects per million opportunities (dpmo) = _____.

A)(Number of defects discovered / Opportunities for error)100,000
B)Opportunities for errorNumber of defects discovered / 1,000,000
C)(Number of defects discovered / Opportunities for error)1,000,000
D)Opportunities for error / (Number of defects discovered

Question 37

Collecting _____ data is usually easier than collecting _____ data because the assessment can usually be done more quickly by a simple inspection or count.

A)variable; attribute
B)conformances; nonconformances
C)attribute; variable
D)simple; complex

Question 38

If the cost of investigating an operation to identify the cause of an apparent out-of-control condition is low,narrower control limits should be selected.

Question 39

In service applications,the term _____ is generally used to describe a nonconformance.

A)error
B)unit
C)cycle
D)trend

Question 40

Variable data are _____.

A)discrete
B)not measurable
C)nonrandom
D)continuous

Question 41

Which of the following is NOT one of the basic applications of a control chart?

A)To calculate the average-range.
B)To establish a state of statistical control.
C)To monitor a process to identify special causes of variation.
D)To determine process capability.

Question 42

Which of the following is NOT an indication of an out-of-control process?

A)Five consecutive points fall on one side of the center line.
B)Four of five consecutive points fall within the outer two-thirds region between the center line and one of the control limits.
C)Two of three consecutive points fall in the outer one-third region between the center line and one of the control limits.
D)A single point falls above the upper control limit.

Question 43

The s-chart is recommended when:

A)the control chart calculations needs to be performed by hand.
B)tight control of variability in the process is required.
C)the-chart is not associated with an R-chart.
D)the sample size for each sample needs to be reduced.

Question 44

Twenty samples of size 6 were collected for a variable measurement.Determine the upper control limit (UCL) and lower control limit (LCL) for an R-chart if the sum of the sample ranges equals 88.0.

A)UCL = 8.8176,LCL = 0.0000
B)UCL = 9.3016,LCL = 0.3344
C)UCL = 13.2000,LCL = 0.0000
D)UCL = 29.3921,LCL = 0.0000

Question 45

Six samples of size 10 were collected.The data are provided in the following table:

The upper control limit (UCL) and lower control limit (LCL) for an s-chart are:

A)LCL = 0.2840,UCL = 1.7160.
B)LCL = 0.0994,UCL = 0.6006.
C)LCL = 4.6256,UCL = 5.3256.
D)LCL = 3.6750,UCL = 5.7750.

Question 46

An alternative to using the R-chart is the:

A)np-chart.
B)s-chart.
C)c-chart.
D)p-chart.

Question 47

Which of the following pairs of charts are used together?

A)-chart and p-chart
B)R-chart and p-chart
C)R-chart and s-chart
D)

Question 48

Short repeated patterns in a control chart,with alternating high peaks and low valleys,are known as:

A)trends.
B)cycles.
C)shifts.
D)runs.

Question 49

A precision parts manufacturer produces bolts for use in military aircraft.The specifications for bolt length are 37.50 $\pm$ 0.25 cm.The company has established an
-chart and an R-chart using samples of size five.The center lines for the
-chart and R-chart are set at 35.25 cm and 1.08 cm,respectively.What is the value of C_p for this process?

A)0.179
B)1.333
C)0.301
D)0.166

Question 50

For variables data,the sample means are assumed to be:

A)exponentially distributed.
B)normally distributed.
C)Poisson distributed.
D)binomially distributed.

Question 51

A machined part has a lower specification limit of 3.5 inches and an upper specification limit of 3.9 inches.The range for the pre-control green zone is:

A)3.5 inches to 3.9 inches.
B)3.8 inches to 3.9 inches.
C)less than 3.5 inches.
D)3.6 inches to 3.8 inches.

Question 52

A company wishes to monitor the variation in the length of time it takes to process and send a bill to a customer.Seven bills will be randomly selected each day for a 60-day period and the length of time it takes to process and send the bill to a customer will be recorded for each bill.The appropriate control chart is a(n):

A)-chart.
B)R-chart.
C)p-chart.
D)u-chart.

Question 53

Statistical process control relies on _____.

A)process capability studies
B)dashboards
C)control charts
D)metrology

Question 54

A _____ is the result of some cause that gradually affects the quality characteristics of the product and causes the points on a control chart to gradually move up or down from the center line.

A)defect
B)process shift
C)cycle
D)trend

Question 55

Control limits are often confused with _____.

A)pre-control lines
B)center lines
C)specification limits
D)three sigma limits

Question 56

Which of the following is a likely cause of the control chart pattern known as a "trend?"

A)Aging equipment
B)Maintenance schedules
C)New process operator
D)Sudden power surge

Question 57

If the process mean and variance do not change over time,the process is considered to be:

A)in statistical control.
B)normally distributed.
C)stable.
D)capable.

Question 58

The _____ is used to monitor the centering of the process.

A)-chart
B)R-chart
C)p-chart
D)np-chart

Question 59

A precision parts manufacturer produces bolts for use in military aircraft.The specifications for bolt length are 37.50 $\pm$ 0.25 cm.The company has established an
-chart and an R-chart using samples of size five.The center lines for the
-chart and R-chart are set at 37.35 cm and 1.05 cm,respectively.What is the value of C_pk for this process?

A)0.07
B)0.28
C)0.75
D)0.03

Question 60

In determining whether a process is in statistical control,the _____ is/are generally analyzed first.

A)R-chart
B)upper and lower control limits
C)-chart
D)center line

Question 61

For statistical process control,a good sampling method should always:

A)use samples of random measurements over a long period of time.
B)minimize sampling cost.
C)maximize sample size.
D)use rational subgroups.

Question 62

Which of the following charts is used to monitor the average number of nonconformances per unit when sample sizes vary?

A)-chart
B)c-chart
C)p-chart
D)u-chart

Question 63

All else being constant,if the sample size in a p-chart increases from 100 to 120,the upper and lower control limits will:

A)move farther apart.
B)move closer together.
C)not be affected.
D)both shift upward.

Question 64

Define the term statistical process control.Outline the steps for setting up a control chart to monitor a process.

Question 65

Discuss the differences between attributes and variables data.

Question 66

A _____ monitors the fraction of nonconforming units.

A)c-chart
B)u-chart
C)np-chart
D)p-chart

Question 67

A specification is 50.0 cm $\pm$ 10.0 cm.Sketch and label the pre-control zones for this specification.Include the following values on your sketch: nominal,upper and lower specification limits,and end points of the green zone.

Question 68

The control chart most appropriate for plotting the daily percentage of students that wait longer than 5 minutes in line at the undergraduate admissions office is a(n):

A)p-chart.
B)np-chart.
C)x-chart.
D)

Question 69

Define pre-control and explain under what conditions pre-control can be used.

Question 70

If the lower limit for a p-chart computes to a number less than zero,this indicates:

A)that a calculation error has been made.
B)that the process is out of control.
C)that an attribute measure is incorrectly used.
D)that the lower limit should be set at zero.

Question 71

A delivery company defines a "defect" as a package delivered later than the promised delivery time.Management wants to monitor the proportion of such defect packages per week and plans to sample 120 packages every week.The appropriate control chart is a(n):

A)-chart.
B)R-chart.
C)p-chart.
D)np-chart.

Question 72

To form rational subgroups for an
-chart,the goal is to choose the samples as _____ as possible.

A)heterogeneous
B)homogeneous
C)large
D)systematic

Question 73

A canning company defines a "nonconformance" as an orange juice can whose diameter is beyond the upper specification limit.A manager at the canning company wants to monitor the number of such orange juice cans produced per day.Each day,an employee will randomly select 120 cans over a period of four weeks.The employee then determines and plots the number of nonconformance cans in each sample.The appropriate control chart is a(n):

A)u-chart.
B)R-chart.
C)p-chart.
D)np-chart.

Question 74

The sample size for an x-chart:

A)should be between 25 and 30.
B)is larger than that for an-chart.
C)is equal to one.
D)should be greater than one.

Question 75

c-charts are based on the _____ probability distribution.

A)normal
B)binomial
C)Poisson
D)exponential

Question 76

x-charts are used for:

A)averages of variables data.
B)individual attributes data.
C)individual variables data.
D)averages of attributes data.

Question 77

Which of the following is CORRECT regarding an x-chart?

A)Individual data require averaging before being plotted on it.
B)It is less sensitive to many conditions that can be detected by-chart and R-chart.
C)Specification limits cannot be drawn on the chart for direct comparison with the control limits.
D)The assumption of normality of observations is less critical than for

Question 78

Which of the following is a major advantage of np-charts?

A)They can be used for variable sample sizes.
B)They are more accurate than p-charts.
C)They are easier to understand for production personnel.
D)The control limits are based on binomial distribution.

Question 79

Each day,a manufacturing company producing circuit boards will randomly sample 60 circuit boards for a period of 25 days and then determine and plot the number of defects contained in each of these boards.The appropriate control chart is a(n):

A)u-chart.
B)p-chart.
C)np-chart.
D)c-chart.

Question 80

Because of high test costs,a sample of single wastewater sludge is tested daily for dissolved oxygen content.The appropriate control chart is:

A)-chart and R-chart.
B)u-chart.
C)x-chart and moving range chart.
D)x-chart and R-chart.