Deck 23 Managing Quality

Question 1

To measure the voltage of batteries, one would sample by attributes.

Answer 1

False

Question 2

The x-bar chart, like the c-chart, is based on the exponential distribution.

Answer 2

False

Question 3

The higher the process capability ratio, the greater the likelihood that process will be within design specifications.

Answer 3

True

Question 4

Some degree of variability is present in almost all processes.

Question 5

X-bar charts are used when we are sampling attributes.

Question 6

Mistakes stemming from workers' inadequate training represent an assignable cause of variation.

Question 7

In statistical process control, the range often substitutes for the standard deviation.

Question 8

A process is said to be in statistical control when assignable causes are the only sources of variation.

Question 9

Mean charts and range charts complement one another, one detecting shifts in process average, the other detecting shifts in process dispersion.

Question 10

A process range chart illustrates the amount of variation within the samples.

Question 11

The Central Limit Theorem states that when the sample size increases, the distribution of the sample means will approach the normal distribution.

Question 12

The C_pk index measures the difference between desired and actual dimensions of goods or services produced.

Question 13

A p-chart is appropriate to plot the number of typographic errors per page of text.

Question 14

If the process average is in control, then the process range must also be in control.

Question 15

Averages of small samples, not individual measurements, are generally used in statistical process control.

Question 16

A process that is in statistical control will always yield products that meet their design specifications.

Question 17

A normal distribution is generally described by its two parameters: the mean and the range.

Question 18

A c-chart is appropriate to plot the number of flaws in a bolt of fabric.

Question 19

The purpose of process control is to detect when natural causes of variation are present.

Question 20

The x-bar chart indicates that a gain or loss of uniformity has occurred in dispersion of a production process.

Question 21

Natural variations

A) are variations that are to be identified and investigated
B) are variations that can be traced to a specific cause
C) are the same as assignable variations
D) lead to occasional false findings that processes are out of control
E) play no role in statistical process control

Question 22

A process that is assumed to be in control with limits of 89 +/- 2 had sample averages of the following 87.1, 87, 87.2, 89, 90, 89.5, 88.5, and 88. Is the process in control?

A) Yes
B) No, one or more averages exceeded the limits.
C) Not enough information to tell.
D) No, there is a distinguishable trend.
E) No, two or more consecutive points are very near the lower (or upper) limit.

Question 23

In acceptance sampling, a manager can reach the wrong conclusion if the sample is not representative of the population it was drawn from.

Question 24

The causes of variation in statistical process control are

A) cycles, trends, seasonality, and random variations
B) producer's causes and consumer's causes
C) mean and range
D) natural causes and assignable causes
E) Type I and Type II

Question 25

The probability of rejecting a good lot is known as consumer's risk.

Question 26

Natural variations

A) affect almost every production process
B) are the many sources of variation that occur when a process is under control
C) when grouped, form a pattern, or distribution
D) are tolerated, within limits, when a process is under control
E) All of the above are true.

Question 27

The number of defects after a hotel room cleaning (sheets not straight, smears on mirror, missed debris on carpet, etc) should be measured using a(n)

A) x-bar chart
B) R-chart
C) p-chart
D) c-chart
E) either x-bar or R chart

Question 28

The upper and lower limits for diving ring diameters made by John's Swimming are 40 and 39 cm. John took 11 samples with the following average diameters (39, 39.1, 39.2, 39.3, 39.4, 39.5 39.6, 39.7, 39.8, 39.9, 40). Is the process in control?

A) Yes, no diameters exceeded the control limits.
B) No, some diameters exceeded the control limits.
C) No, there is a distinguishable pattern to the samples.
D) No, the range is not in control.
E) There is not enough information to make a decision.

Question 29

A lot that is accepted by acceptance sampling is certified to be free of defects.

Question 30

Red Top Cab Company receives multiple complaints per day about driver behavior. Over 9 days the owner recorded the number of calls to be 3, 0, 8, 9, 6, 7, 4, 9, 8. What is the upper control limit for the c-chart?

A) 13.35
B) 8.45
C) 24.00
D) 0.00
E) 9.03

Question 31

Acceptance sampling accepts or rejects an entire lot based on the information contained in the sample.

Question 32

The number of late insurance claim payouts per 100 should be measured with a

A) x-bar chart
B) R-chart
C) p-chart
D) c-chart
E) either a p or c chart

Question 33

Control charts for variables are based on data that come from

A) acceptance sampling
B) individual items
C) averages of small samples
D) averages of large samples
E) the entire lot

Question 34

Assignable variation

A) is a sign that a process is under control
B) is to be identified and investigated
C) is the same as random variation
D) is variation that cannot be traced to a specific cause
E) leads to a steep OC curve

Question 35

Assignable causes

A) are not as important as natural causes
B) are within the limits of a control chart
C) depend on the inspector assigned to the job
D) are also referred to as "chance" causes
E) are causes of variation that can be identified and investigated

Question 36

The steeper an OC curve, the better it discriminates between good and bad lots.

Question 37

If a sample of items is taken and the mean of the sample is outside the control limits the process is

A) out of control and the cause should be established
B) in control, but not capable of producing within the established control limits
C) within the established control limits with only natural causes of variation
D) monitored closely to see if the next sample mean will also fall outside the control limits
E) producing high quality products

Question 38

An acceptance sampling plan must define "good lots" and "bad lots" and specify the risk level associated with each one.

Question 39

The purpose of an x-bar chart is to determine whether there has been a

A) change in the dispersion of the process output
B) change in the percent defective in a sample
C) change in the central tendency of the process output
D) change in the number of defects in a sample
E) change in the AOQ

Question 40

The acceptable quality level (AQL) is the average level of quality we are willing to accept.

Question 41

Statistical process control charts

A) display the measurements on every item being produced
B) display upper and lower limits for process variables or attributes, and signal when a process is no longer in control
C) indicate to the process operator the average outgoing quality of each lot
D) indicate to the operator the true quality of material leaving the process
E) none of the above

Question 42

If = 23 ounces, σ = 0.4 ounces, and n = 16, the ±3σ control limits will be

A) 21.8 to 24.2 ounces
B) 23 ounces
C) 22.70 to 23.30 ounces
D) 22.25 to 23.75 ounces
E) none of the above

Question 43

Up to three standard deviations above or below the centerline is the amount of variation that statistical process control allows for

A) Type I errors
B) about 95.5% variation
C) natural variation
D) all types of variation
E) assignable variation

Question 44

The type of inspection that classifies items as being either good or defective is

A) variable inspection
B) attribute inspection
C) fixed inspection
D) all of the above
E) none of the above

Question 45

Which of the following was Unisys Corp.'s failed quality measure in its management of Florida Health Care Services?

A) percentage of claims processed with errors
B) percentage of claims processed within 30 days
C) number of claims processed per month
D) number of claims denied
E) both A and B

Question 46

The mean and standard deviation for a process for which we have a substantial history are µ = 120 and σ = 2. For the x-bar chart, a sample size of 16 will be used. What is the mean of the sampling distribution?

A) 1/8 (0.125)
B) 7.5
C) 2
D) 40
E) 120

Question 47

The p-chart tells us whether there has been a

A) gain or loss in dispersion
B) change in the percent defective in a sample
C) change in the central tendency of the process output
D) change in the number of defects in a sample
E) none of the above

Question 48

A manager wishes to build a 3-sigma range chart for a process. The sample size is five, the mean of sample means is 16.01, and the average range is 5.3. From Table S6.1, the appropriate value of D₃ is 0, and D₄ is 2.115. The UCL and LCL for this range chart are

A) 33.9 and 11.2
B) 33.9 and 0
C) 11.2 and 0
D) 6.3 and 0
E) 31.91 and 0.11

Question 49

A manager wants to build 3-sigma control limits for a process. The target value for the mean of the process is 10 units, and the standard deviation of the process is 6. If samples of size 9 are to be taken, the UCL and LCL will be

A) -8 and 28
B) 16 and 4
C) 12 and 8
D) 4 and 16
E) 8 and 12

Question 50

Ten samples of a process measuring the number of returns per 100 receipts were taken for a local retail store. The number of returns were 10, 9, 11, 7, 3, 12, 8, 4, 6, 11. Find the standard deviation of the sampling distribution. (Hint- Use p-bar formula)

A) There is not enough information.
B) .081
C) 8.1
D) .0273
E) .0863

Question 51

For an x-bar chart where the standard deviation is known, the Upper Control Limit

A) is 3 . σ below the mean of sample means for a 3σ control chart
B) is 3 . σ above the mean of sample means for a 3σ control chart
C) is 3 . σ/ below the mean of sample means for a 3σ control chart
D) is 3 . σ/ above the mean of sample means for a 3σ control chart
E) Cannot be calculated unless the average range is known.

Question 52

Jars of pickles are sampled and weighed. Sample measures are plotted on control charts. The ideal weight should be precisely 11 oz. Which type of chart(s) would you recommend?

A) p-charts
B) c-charts
C) - and R-charts
D) -, but not R-charts
E) both p- and c-charts

Question 53

An x-bar control chart was examined and no data points fell outside of the limits. Can this process be considered in control?

A) No, there could be a pattern to the points.
B) No, the R-chart must be checked.
C) No, the number of samples must be known.
D) Yes
E) Both A and B

Question 54

Consumer's risk is the probability of

A) accepting a good lot
B) rejecting a good lot
C) rejecting a bad lot
D) accepting a bad lot
E) none of the above

Question 55

Which of the following is true of a p-chart?

A) The lower control limit is found by subtracting a fraction from the average number of defects.
B) The lower control limit indicates the minimum acceptable number of defects.
C) The lower control limit equals D₃ times p-bar.
D) The lower control limit may be at zero.
E) The lower control limit is the same as the lot tolerance percent defective.

Question 56

According to the text, the most common choice of limits for control charts is usually

A) ± 1 standard deviation
B) ± 2 standard deviations
C) ± 3 standard deviations
D) ± 3 standard deviations for means and ± 2 standard deviations for ranges
E) none of the above

Question 57

Plots of sample ranges indicate that the most recent value is below the lower control limit. What course of action would you recommend?

A) Since there is no obvious pattern in the measurements, variability is in control.
B) One value outside the control limits is insufficient to warrant any action.
C) Lower than expected dispersion is a desirable condition; there is no reason to investigate.
D) The process is out of control; reject the last units produced.
E) Variation is not in control; investigate what created this condition.

Question 58

The Central Limit Theorem

A) is the theoretical foundation of the c-chart
B) states that the average of assignable variations is zero
C) allows managers to use the normal distribution as the basis for building some control charts
D) states that the average range can be used as a proxy for the standard deviation
E) controls the steepness of an operating characteristic curve

Question 59

The usual purpose of an R-chart is to signal whether there has been a

A) gain or loss in dispersion
B) change in the percent defective in a sample
C) change in the central tendency of the process output
D) change in the number of defects in a sample
E) none of the above

Question 60

To set -chart upper and lower control limits, one must know the process central line, which is the

A) average of the sample means
B) total number of defects in the population
C) percent defects in the population
D) size of the population
E) average range

Question 61

Acceptance sampling's primary purpose is to

A) estimate process quality
B) identify processes that are out of control
C) detect and eliminate defectives
D) decide if a lot meets predetermined standards
E) determine whether defective items found in sampling should be replaced

Question 62

Acceptance sampling

A) may involve inspectors taking random samples (or batches) of finished products and measuring them against predetermined standards
B) may involve inspectors taking random samples (or batches) of incoming raw materials and measuring them against predetermined standards
C) is more economical than 100% inspection
D) may be either of a variable or attribute type, although attribute inspection is more common in the business environment
E) All of the above are true.

Question 63

Which of the following statements on acceptance sampling is true?

A) Acceptance sampling draws samples from a population of items, tests the sample, and accepts the entire population if the sample is good enough, and rejects it if the sample is poor enough.
B) The sampling plan contains information about the sample size to be drawn and the critical acceptance or rejection numbers for that sample size.
C) The steeper an operating characteristic curve, the better its ability to discriminate between good and bad lots.
D) All of the above are true.
E) All of the above are false.

Question 64

The process capability measures C_p and C_pk differ because

A) only one ensures the process mean is centered within the limits
B) C_p values above 1 indicate a capable process, C_pk values above 2 indicate a capable process
C) both are identical
D) C_p values for a given process will always be greater than or equal to C_pk values
E) both A and D

Question 65

A nationwide parcel delivery service keeps track of the number of late deliveries (more than 30 minutes past the time promised to clients) per day. They plan on using a control chart to plot their results. Which type of control chart(s) would you recommend?

A) - and R-charts
B) p-charts
C) c-charts
D) -, but not R-charts
E) both p- and c-charts

Question 66

The local newspaper receives several complaints per day about typographic errors. Over a seven-day period, the publisher has received calls from readers reporting the following number of errors: 4, 3, 2, 6, 7, 3, and 9. Based on these data alone, what type of control chart(s) should the publisher use?

A) p-chart
B) c-chart
C) -chart
D) R-chart
E) - and R-charts

Question 67

If the C_pk index exceeds 1

A) the AQL must be smaller than the LTPD
B) σ must be less than one-third of the absolute value of the difference between each specification and the process mean
C) the x-bar chart must indicate that the process is in control
D) the process is capable of Six Sigma quality
E) the process is characterized as "not capable"

Question 68

A C_p of 1.33 indicates how many sigma limits

A) 1
B) 1.33
C) 2
D) 3
E) 4

Question 69

The normal application of a p-chart is in

A) process sampling by variables
B) acceptance sampling by variables
C) process sampling by attributes
D) acceptance sampling by attributes
E) none of the above

Question 70

An acceptance sampling plan's ability to discriminate between low quality lots and high quality lots is described by

A) a Gantt chart
B) the Central Limit Theorem
C) a process control chart
D) an operating characteristics curve
E) a range chart

Question 71

The c-chart signals whether there has been a

A) gain or loss in uniformity
B) change in the number of defects per unit
C) change in the central tendency of the process output
D) change in the percent defective in a sample
E) change in the AOQ

Question 72

Acceptance sampling is usually used to control

A) the number of units output from one stage of a process which are then sent to the next stage
B) the number of units delivered to the customer
C) the quality of work-in-process inventory
D) incoming lots of purchased products
E) all of the above

Question 73

An operating characteristic (OC) curve describes

A) how many defects per unit are permitted before rejection occurs
B) the sample size necessary to distinguish between good and bad lots
C) the most appropriate sampling plan for a given incoming product quality level
D) how well an acceptance sampling plan discriminates between good and bad lots
E) none of the above

Question 74

The statistical process chart used to control the number of defects per unit of output is the

A) -chart
B) R-chart
C) p-chart
D) AOQ chart
E) c-chart

Question 75

Acceptance sampling

A) is the application of statistical techniques to the control of processes
B) was developed by Walter Shewhart of Bell Laboratories
C) is used to determine whether to accept or reject a lot of material based on the evaluation of a sample
D) separates the natural and assignable causes of variation
E) all of the above

Question 76

A manufacturer uses statistical process control to control the quality of the firm's products. Samples of 50 of Product A are taken, and a defective/acceptable decision is made on each unit sampled. For Product B, the number of flaws per unit is counted. What type(s) of control charts should be used?

A) p-charts for A and B
B) p-chart for A, c-chart for B
C) c-charts for both A and B
D) p-chart for A, mean and range charts for B
E) c-chart for A, mean and range charts for B

Question 77

A C_pk index of 1.00 equates to a defect rate of

A) five percent
B) 3.4 defects per million
C) 2.7 per 1,000 items
D) 97.23 percent
E) one percent

Question 78

A run test is used

A) to examine variability in acceptance sampling plans
B) in acceptance sampling to establish control
C) to examine points in a control chart to check for natural variability
D) to examine points in a control chart to check for nonrandom variability
E) none of the above

Question 79

The statistical definition of Six Sigma allows for 3.4 defects per million. This is achieved by a C_pk index of

A) 0
B) 1
C) 1.33
D) 1.67
E) 2

Question 80

Which of the following is true regarding the process capability index C_pk?

A) A C_pk index value of 1 is ideal, meaning all units meet specifications.
B) The larger the C_pk, the more units meet specifications.
C) The C_pk index can only be used when the process centerline is also the specification centerline.
D) Positive values of the C_pk index are good; negative values are bad.
E) None of the above is true.