Deck 21: Statistical Process Control

Question 1

Assignable variation is caused by specific events or factors that are frequently temporary.

Answer 1

True

Question 2

Chance variation in general cannot be eliminated without changing the process.

Answer 2

True

Question 3

Which of the following is an example of chance variation in a process?

A)Two randomly selected boxes of cereal that don't weigh exactly 16 ounces (the labeled weight).
B)Two randomly selected boxes of cereal that don't weigh exactly the same.
C)Normal fluctuations in the process that randomly occur.
D)None of these choices.

Answer 3

None of these choices.

Question 4

Variations in a process that are caused by specific events or factors that are frequently temporary and can usually be identified and eliminated are known as:

A)chance variation.
B)common variation.
C)assignable variation.
D)All of these choices are true.

Question 5

The centerline of an control chart is the mean of the samples being collected.

Question 6

In statistical process control,a Type I error occurs if we conclude that the process is in control when it actually isn't.

Question 7

A new machine can cause a change in the mean of a process distribution.This is a result of a level shift.

Question 8

When the control chart shows a slow and steady shift (up or down)in the process distribution mean,the result is referred to as:

A)a level shift.
B)a cycle.
C)a trend.
D)instability.

Question 9

How do we know when a process is in control?

A)The control chart shows sample means that are randomly distributed between the control limits.
B)Each observation sampled is drawn from an identical distribution.
C)The control chart shows no patterns or cycles in the plotted sample means.
D)All of these choices are true.

Question 10

Chance variation was built into the produce when the production process was first set up.

Question 11

When the control chart shows a repeated series of small observations followed by large observations,the result is referred to as:

A)a cycle.
B)a trend.
C)a level shift.
D)instability.

Question 12

If a machine part is slowly losing its ability to work,causing the standard deviation of the process to increase,this is an example of assignable variation called a trend.

Question 13

If the average run length of a process is 385,then the control chart will wrongly conclude that the process is out of control once every 385 samples on average.

Question 14

In statistical process control,a Type II error occurs if we conclude that the process is in control when it actually isn't.

Question 15

Which of the following process results indicate that a statistical process is out of control?

A)A repeated series of small observations followed by large observations.
B)An increase in the standard deviation.
C)A slow and steady shift (up or down)in the process distribution mean.
D)All of these choices are true.

Question 16

Variations in a process that are caused by a number of randomly occurring events that cannot be eliminated without changing the process are known as:

A)assignable variation.
B)common variation.
C)special variation.
D)None of these choices.

Question 17

Which of the following is an example of assignable variation in a process?

A)The valve on the machine that fills paint cans has malfunctioned.
B)The operator of the paint filling machine experiences fatigue during his shift.
C)A temperature or humidity change has occurred in the factory.
D)All of these choices are true.

Question 18

If the average run length of a process is 385,that means the sample size should be 385 for each sample collected.

Question 19

A malfunctioning valve in a filling machine can create assignable variation.

Question 20

A predictable change in operators for the day shift and night shift can create assignable variation called a cycle.

Question 21

Suppose previously your company decided that a process is out of control when the mean shifts by about 1 standard deviation.Now your company wants to declare a process as being out of control when the mean shifts by .50 standard deviations.In order to do this,the samples must be collected ____________________ often and/or the sample sizes must be ____________________.

Question 22

A level shift is a change in the ____________________ of the process distribution.

Question 23

____________________ variation is caused by specific events or factors that are frequently temporary.

Question 24

The lower and upper control limits of an control chart are usually set at:

A)± one standard error from the centerline.
B)± two standard errors from the centerline.
C)± three standard errors from the centerline.
D)None of these choices.

Question 25

An chart for a normally distributed random variable has control limits set at ±3 standard errors from the centerline.One sample mean falls outside the control limits when the process is actually under control.The probability that this happened by chance is:

A).997
B).500
C).050
D).003

Question 26

A trend indicates there is a slow and steady shift in the ____________________ of a process distribution.

Question 27

Which of the following elements affects the chance of making a Type II error?

A)The sample size.
B)The mean of the process.
C)The chance of making a Type I error.
D)All of these choices are true.

Question 28

The average run length indicates how often a false alarm is expected to occur.That is,the average run length is one divided by the probability of a Type ____________________ error.

Question 29

____________________ variation is caused by a number of randomly occurring events that are part of the production process.

Question 30

What do you look for to determine when a process is in a state of statistical control?

A)A control chart with a series of consecutive points that are above the center line and a series of consecutive points that are below the center line.
B)A control chart in which no points fall outside either the upper control limit or the lower control limit and no patterns are present.
C)A control chart in which all the points are exactly the same.
D)All of these choices are true.

Question 31

____________________ is the term used when the standard deviation of a process distribution increases.

Question 32

If the control limits of an chart are set at ±2 standard errors from the centerline instead of the commonly used ±3 standard errors,this will result in

A)an increased chance for a Type I error and a decreased chance for a Type II error.
B)an increased chance for a Type I error and an increased chance for a Type II error.
C)a decreased chance for a Type I error and an increased chance for a Type II error.
D)a decreased chance for a Type I error and a decreased chance for a Type II error.

Question 33

Which of the following is NOT something you can do with an operating characteristic curve?

A)Decide what sample size to use in designing a control chart.
B)Decide how many samples to select in designing a control chart.
C)Find the probability of making a Type I error.
D)Find the probability of making a Type II error.

Question 34

When no point lies outside the control limits of a chart,we conclude that variation in the process is:

A)caused by chance and there is not enough evidence to infer that the process is out of control.
B)caused by chance and there is enough evidence to infer that the process is out of control.
C)caused by assignable causes and there is enough evidence to infer that the process is under control.
D)caused by assignable causes and there is not enough evidence to infer that the process is out of control.

Question 35

In designing a control chart,the statistician must select a sample size and a sampling frequency.These decisions are based on which factors:

A)Cost of making Type I and Type II errors.
B)Length of the production run.
C)Typical change in the process distribution when the process goes out of control.
D)All of these choices are true.

Question 36

When the control chart shows an increase in the standard deviation of the process,the result is referred to as:

A)a trend.
B)a cycle.
C)a level shift.
D)instability.

Question 37

The ____________________ is the expected number of samples that must be taken on average,before the control chart indicates that the process has gone out of control.

Question 38

When the control chart shows a change in the mean of the process distribution,the result is referred to as:

A)a trend.
B)a cycle.
C)a level shift.
D)instability.

Question 39

The key to quality is to detect when the process goes out of control.The ____________________ chart is the statistical method that we use to detect problems.

Question 40

A hypothesis test is used to determine whether there is sufficient evidence to infer that the process mean has changed.This means H₀ is: the process is ____________________ control.

Question 41

Discuss what we mean by assignable variation in a process and give an example.

Question 42

What is the average run length (ARL)until an control chart signals a false alarm if the control limits are set at ±2.5 standard errors from the centerline?

Question 43

Assume that the control limits of an chart are defined as 3 standard errors above and below the centerline.Calculate the probability that a sample mean falls outside the control limits when the process is in fact under control.

Question 44

Suppose you are producing a product implementing statistical process control.
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a.Give an example of assignable variation that would create a level shift.
b.Give an example of assignable variation that would create instability.
c.Give an example of assignable variation that would create a trend.
d.Give an example of assignable variation that would create a cycle.

Question 45

A malfunction in the process goes unnoticed and later causes great expense in terms of operator and machine downtime.What type of error was caused here and how could it be decreased?

Question 46

What are the null and alternative hypotheses used to determine whether or not a process is in control?

Question 47

If you change the control limits from ±3 standard errors from the centerline to ±2 standard deviations from the centerline,this ____________________ the probability of a Type I error and ____________________ the probability of a Type II error.

Question 48

Assume a process has limits set at ±2.5 standard errors from the centerline.The average run length (ARL)is 81.What does this mean?

Question 49

Describe what a Type II error is,and what its impact is,in terms of a production process.

Question 50

Describe what a Type I error is,and what its impact is,in terms of a production process.

Question 51

Describe the three essential parts of a control chart.

Question 52

You stopped a production process because you felt the process was out of control according to your control chart.However,it turns out the process was in control,costing you $20,000 in downtime of the equipment and laborers.This is an example of a costly Type____________ error.

Question 53

For an control chart,you test a series of sample means.For each series of samples,we want to determine whether there is sufficient evidence to infer that the process mean has changed (i.e.reject H₀: the process is under control).Under what situation would you reject the null hypothesis based on the control chart?

Question 54

What is the average run length (ARL)until an control chart signals a false alarm if the control limits are set at ±2 standard errors from the centerline?

Question 55

Discuss what we mean by chance variation in a process and give an example.

Question 56

Assume that the control limits of an chart are defined as 2.5 standard errors above and below the centerline.Calculate the probability that a sample mean falls outside the control limits when the process is in fact under control.

Question 57

A production facility produces 75 units per hour and uses an chart to monitor its quality.The control limits are seat at 2.5 standard errors from the mean.On average,how many units will be produced until the control chart signals that the process is out of control,when it is in fact under control?

Question 58

Assume a process has limits set at ±3 standard errors from the centerline.The average run length (ARL)is 385.What does this mean?

Question 59

What is the average run length (ARL)until an control chart signals a false alarm if the control limits are set at ±3 standard errors from the centerline?

Question 60

Assume that the control limits of an chart are defined as 2 standard errors above and below the centerline.Calculate the probability that a sample mean falls outside the control limits when the process is in fact under control.

Question 61

When the purpose of sampling is to detect when a process becomes too variable,the control chart of choice will be an S chart.

Question 62

If the upper and lower specification limits of a process are .852 and .828,respectively,and the process standard deviation is .002,then the process capability index C_p is

A).024
B)2.000
C)−2.000
D)12.000

Question 63

The mean of the sample means and the pooled standard deviation of 50 samples of size 10 taken from a production process under control are found to be 225 and 16,respectively.The upper control limit for the chart is:

A)231.79
B)240.18
C)218.21
D)209.82

Question 64

Control charts used to determine if the process distribution standard deviation has changed are:

A) and p charts.
B)p and R charts.
C)R and S charts.
D)S and

Charts.

Question 65

A process capability index C_p of 1.0 describes a production where the difference in the specification limits is equal to 6 standard errors.

Question 66

The chart is employed to determine whether the process distribution means have changed.To determine whether the process distribution standard deviation has changed,we use the S (which stands for standard deviation)chart.

Question 67

For an chart,the lower and upper control limits are usually set at three standard errors from the centerline.

Question 68

The process capability index measures the capability of the process to produce units whose dimensions fall outside the specification limits.

Question 69

To determine whether the proportion of defectives is in line with specifications,we use a(n):

A) chart.
B)S chart.
C)p chart.
D)All of these choices are true.

Question 70

The mean of the sample means and the pooled standard deviation of 40 samples of size 9 taken from a production process under control are ,and S = 12,respectively.The lower control limit and the upper control limit of the 3-sigma chart are 408 and 432,respectively.

Question 71

The mean of the sample means and the pooled standard deviation of 36 samples of size 9 taken from a production process under control are ,and S = 6,respectively.The lower control limit of the 3-sigma chart is 147.

Question 72

To determine whether the process distribution standard deviation has changed,we use a(n):

A) chart.
B)S chart.
C)p chart.
D)All of these choices are true.

Question 73

The process capability index measures the capability of the process to produce units whose dimensions fall with in the specifications.

Question 74

A process capability index (C_p)of 2.0 describes a production process where the specification limits are equal to 3 standard errors above and below the centerline.

Question 75

The mean of the sample means and the pooled standard deviation of 25 samples of size 4 taken from a production process under control are found to be 150 and 10,respectively.The centerline for the chart is:

A)150
B)100
C)250
D)6

Question 76

The process capability index is defined as C_p = (USL − LSL)/ 6,where USL and LSL are the upper and lower specification limits.

Question 77

Control charts for variables are appropriate whenever we are interested in monitoring measurements,such as weights,diameters,or temperature.

Question 78

A coffee machine fills cups with an average of 6 ounces with a standard deviation of .25 ounces.A sample of 9 cups is taken.The lower and upper control limits for a 3-sigma control chart are 5.75 and 6.25,respectively.

Question 79

The mean of the sample means and the pooled standard deviation of 40 samples of size 5 taken from a production process under control are found to be 400 and 15,respectively.The lower control limit for the chart is:

A)460.37
B)392.88
C)379.88
D)None of these choices.

Question 80

The chart helps with questions about whether the process is producing the correct or acceptable mean.