Deck 13: Statistical Process Control

Question 1

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

Answer 1

False

Question 2

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

Answer 2

False

Question 3

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

Answer 3

True

Question 4

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

Question 5

The most commonly applied control limits for variables data are 3-sigma control limits.

Question 6

The centerline for the np-chart is equal to the average number of nonconforming items per sample.

Question 7

A "hugging the centerline limit" pattern in a control chart can be the result of using two different lots of material in one process.

Question 8

If all the points on a control chart are within the control limits,then the process is in statistical control.

Question 9

For variables data,the necessary sample size can be estimated by specifying the desired minimum shift in the process mean to be detected.

Question 10

Assignable causes are more difficult to identify in unstable processes.

Question 11

Attribute control charts require larger sample sizes than variable control charts.

Question 12

A p-chart is used with attribute data.

Question 13

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

Question 14

Variation in process output can occur as a result of chance or as a result of assignable causes.

Question 15

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

Question 16

A c-chart is more appropriate than a u-chart if the nature of the process does not yield discrete measurable units of output.

Question 17

If the cost of investigating the cause of an apparent out-of-control situation is high,narrower control limits should be adopted.

Question 18

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

Question 19

The assumption of normality of observations is more critical fo -charts than for x-charts.

Question 20

If the cost of a Type II error is low,narrower control limits should be selected.

Question 21

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 special causes.
D)has control but is not capable.

Question 22

For large samples,and when data are analyzed by computer programs,the _____ is a better measure of variability.

A)variation in control limits
B)tolerance variance
C)median range
D)standard deviation

Question 23

The acronym "SPC" stands for:

A)statistical probability charting.
B)statistical performance control.
C)statistical process control.
D)scientific problem solving.

Question 24

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

A)attribute; variable
B)concrete; continuous
C)random; discrete
D)simple; continuous

Question 25

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

A)R-chart
B)control limits
C)average range
D)nonconformance

Question 26

A process is deemed "out of control" when:

A)common causes are present.
B)special causes are present.
C)data varies around the mean.
D)random variation is present.

Question 27

A(n)_____ 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)instability
B)process shift
C)cycle
D)trend

Question 28

Control limits are often confused with _____.

A)control charts
B)tolerance limits
C)specification limits
D)variance limits

Question 29

Variable measurements are generally expressed as _____ and _____.

A)percentages; ratios
B)averages; standard deviations
C)median values; approximates
D)upper limits; lower limits

Question 30

Control limits relate to _____,while specification limits relate to individual measurements.

A)values within the upper and lower control limits
B)total values in the range
C)median values
D)averages of samples

Question 31

Statistical process control relies on _____.

A)capability models
B)variance analyses
C)control charts
D)conformance reports

Question 32

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 controlled variance.
D)within capability.

Question 33

Variable data are _____.

A)discrete
B)discontinuous
C)random
D)continuous

Question 34

In service applications,we generally use the term _____ to describe a nonconformance.

A)error
B)defect
C)mistake
D)concern

Question 35

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 and signal when the process goes out of control.
D)To determine process capability.

Question 36

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

A)a more distributed population
B)a larger range of variance
C)a larger sample
D)a smaller sample

Question 37

A _____ monitors the fraction of nonconforming items.

A)p-chart
B)x-chart
C)s-chart
D)c-chart

Question 38

A(n)_____ is a performance characteristic that is either present or absent in the product or service under consideration.

A)variable
B)control limit
C)attribute
D)performance range

Question 39

If a unit of work has one or more nonconformances,we term the entire unit _____.

A)dysfunctional
B)out of variance
C)nonconforming
D)static

Question 40

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

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

Question 41

Five samples of size 3 were collected for a variable measurement.All sample data were greater than or equal to 4.0.The sample means and sample ranges are provided in the following table.

The values of which sample are identical?

A)sample 1
B)sample 2
C)sample 3
D)sample 4

Question 42

A p-chart is also called a:

A)pre-control chart.
B)probability chart.
C)fraction defective chart.
D)process capability chart.

Question 43

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 44

A delivery company defines a "defect" as a package delivered later than the promised delivery time.Management wants to monitor the proportion of packages per week delivered beyond their promised delivery time.Management plans to sample 150 packages per week.The appropriate control chart is a(n):

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

Question 45

A manager at a canning company wants to monitor the number of orange juice cans it produces each day that are beyond the upper specification limit for can diameter.Each day an employee will randomly select 150 cans and then determine and plot the number of cans that are beyond the upper specification limit for can diameter.The appropriate control chart is a(n):

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

Question 46

The s-chart is recommended when:

A)the sample size equals one.
B)tight control of variability is required.
C)loose control of variability is acceptable.
D)the sample size needs to be reduced.

Question 47

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

A)in control.
B)symmetric.
C)stable.
D)capable.

Question 48

A) 0.08
B) 0.28
C) 0.75
D) 0.03

Question 49

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

A)Aging equipment
B)Change in setup method
C)New operator
D)A mixture of two materials

Question 50

Determine the sample standard deviation for the following sample data: 7,9,2,0,1,and 5.

A)3.347
B)3.266
C)2.993
D)3.578

Question 51

A) 0.188
B) 1.333
C) 0.301
D) 0.166

Question 52

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 53

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

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

Question 54

A company wishes to monitor the variation in the length of time it takes to process and send a bill to a customer.Five bills will be randomly selected each day 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 55

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 56

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

A)trends.
B)cycles.
C)spikes.
D)reciprocals.

Question 57

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) -chart and R-chart

Question 58

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

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

Question 59

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

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

Question 60

An alternative to using the R-chart is the:

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

Question 61

An -chart is used to monitor the process:

A)range.
B)median.
C)variance.
D)mean.

Question 62

The control chart most appropriate for data that represent the average number of packing slip errors per package shipped each day is the:

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

Question 63

Which of the following charts is used to monitor the total number of defects per unit when a constant subgroup size is employed?

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

Question 64

c-charts are based on the _____ probability distribution.

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

Question 65

In an -chart,the upper control limit is equal to the overall sample mean plus three times the:

A)process standard deviation.
B)average range.
C)standard error of the mean.
D)sample variance.

Question 66

Fifteen samples,of size 100 were collected and a total of 96 nonconforming items were found.The 3-sigma upper control limit for a p-chart would be:

A)0.066.
B)0.083.
C)0.137.
D)0.254.

Question 67

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 68

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 69

x-charts are used for:

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

Question 70

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

A)require frequent sampling.
B)minimize sampling cost.
C)maximize sample size.
D)use rational sub-groups.

Question 71

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)remain the same distance apart.
D)both shift upward.

Question 72

The sample size for an x-chart:

A)should be greater than or equal to 30.
B)is larger than that for an -chart.
C)is equal to one.
D)depends on the number of measurements taken.

Question 73

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

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

Question 74

To form rational sub-groups for an -chart,the goal is to have the samples be as _____ as possible.

A)heterogeneous
B)homogeneous
C)large
D)equally spaced

Question 75

In the application of control charts,as the sample size is increased:

A)Type I errors are reduced, and Type II errors are increased.
B)Type I errors are increased, and Type II errors are reduced.
C)both Type I and Type II errors are increased.
D)both Type I and Type II errors are reduced.

Question 76

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)an out of control process.
C)an incorrect use of an attribute measure.
D)that the limit should be set at zero.

Question 77

Which of the following would be used to monitor the number of nonconforming items?

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

Question 78

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

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

Question 79

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) -chart.

Question 80

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 -chart and R-charts.