Question 1

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.

Accepted Answer

Control charts for variables are based on data that come from averages of small samples, typically with a sample size of 2 to 10. These data are used to monitor and control the variability of a process.

Question 2

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

Accepted Answer

Acceptance sampling does not certify that a lot is free of defects but rather provides a level of confidence that a certain percentage of the lot is defect-free based on the sample size and acceptance criteria chosen.

Question 3

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 Operating Characteristics curve.

Accepted Answer

Assignable variation is a type of variation that can be traced back to a specific cause or source. It is also known as special cause variation. Therefore, if assignable variation occurs, it should be identified and investigated to determine the cause so that corrective action can be taken to eliminate it. This is in contrast to random variation (also known as common cause variation), which is inherent in a process and represents the expected level of variation when the process is operating under stable conditions.

Question 4

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.

Accepted Answer

All of the given statements are true. Natural variations occur in almost every production process, and they are the sources of variation that occur when the process is under control. These variations, when grouped, form a pattern or distribution, and are tolerated within limits when the process is under control.

Question 5

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

Accepted Answer

The probability of rejecting a good lot is known as producer's risk, while consumer's risk is the probability of accepting a bad lot.

Question 6

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.

Accepted Answer

The c-chart is used for counting defects when the number of opportunities for defects is constant. In this case, the number of defects in a hotel room cleaning process (like sheets not straight, smears on mirror, missed debris on carpet) can be counted, making the c-chart the appropriate choice.

Question 7

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.

Accepted Answer

The samples show a clear and consistent upward trend, which indicates a process that is not in control despite all values being within the specified limits.

Question 8

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.

Accepted Answer

The answer of Natural variations
A) are variations that are to...

Question 9

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

Accepted Answer

The Acceptable Quality Level (AQL) is the maximum percentage or proportion of nonconforming items in a batch that, for purposes of sampling inspection, can be considered satisfactory as a process average. It is not an average level of quality but a threshold.

Question 10

The number of late insurance claim payouts per 100 should be measured with a(n)
A) x-bar chart.
B) R-chart.
C) p-chart.
D) c-chart.
E) either a p or c chart.

Accepted Answer

The p-chart is designed to measure the proportion of nonconforming items in a sample, which is exactly what is needed in this scenario. The number of late insurance claim payouts per 100 is a proportion and can be plotted on a p-chart with upper and lower control limits to monitor the process over time. The x-bar chart is used for continuous variables, the R-chart is used for variables with a range or variation, and the c-chart is used for count data, but not appropriate for proportion-based data such as this. Therefore, the best choice is a p-chart.

Question 11

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.

Accepted Answer

The causes of variation in statistical process control are divided into two categories: natural causes (also called common causes) and assignable causes (also called special causes). Natural causes are the inherent sources of variation that are present in any process, while assignable causes are specific events or factors that cause a process to deviate from its normal operation. Therefore, choice D is the best answer as it correctly identifies the two types of causes of variation in statistical process control.

Question 12

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

Accepted Answer

If the sample is not representative of the population, the conclusion drawn from the sample may not accurately reflect the characteristics of the population. This can lead to incorrect decisions and actions based on incomplete or inaccurate information.

Question 13

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.

Accepted Answer

An x-bar chart helps to determine whether the central tendency of the process output has changed. It tracks the average of a sample over time and compares it to the process mean to identify any shifts or trends. It is not designed to detect changes in dispersion, percent defective, number of defects, or AOQ.

Question 14

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

Accepted Answer

Acceptance sampling makes a decision about the entire lot based on a sample of items. If the sample meets the acceptability criteria, the entire lot is accepted; otherwise, it is rejected.

Question 15

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.

Accepted Answer

The answer of A process that is assumed to be...

Question 16

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

Accepted Answer

To calculate the upper control limit for a c-chart, we use the formula UCL = c + 3*(sqrt(c)), where c is the average number of complaints per day. First, we calculate the mean:

Mean = (3+0+8+9+6+7+4+9+8)/9 = 6.44

Then we plug in the mean and solve for UCL:

UCL = 6.44 + 3*(sqrt(6.44)) = 13.35

Therefore, the upper control limit for the c-chart is 13.35.

Question 17

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

Accepted Answer

A steeper operating characteristics curve signifies that the test is better at distinguishing between acceptable and unacceptable lots.

Question 18

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.

Accepted Answer

If the mean of the sample is outside the control limits, it indicates that there is a special cause of variation present in the process. Therefore, the process is out of control, and the cause of the issue should be identified and corrected to prevent further non-conforming products from being produced.

Question 19

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

Accepted Answer

An acceptance sampling plan defines the criteria for "good lots" and "bad lots" and specifies the level of risk associated with accepting a bad lot. The plan also outlines the sample size and acceptance or rejection criteria based on the level of inspection risk.

Question 20

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.

Accepted Answer

Assignable causes, also known as "special causes," are specific factors that can be identified and corrected. They are distinct from "common causes" of variation, which are inherent to the process.

Quiz 26: Statistical Process Control

Control charts for variables are based on data that come from

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

Assignable variation

Natural variations

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

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)

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?

Natural variations

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

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

The causes of variation in statistical process control are

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

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

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

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?

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?

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

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

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

Assignable causes