Question 1

Control charts for variables are based on data that come from

Accepted Answer

Control charts for variables are based on data that come from averages of small samples. This is because variables can have natural variation, and by taking small samples, we can track this variation over time and establish control limits to determine when a process is out of control.

Question 2

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 manager may accept a batch of products that actually does not meet the required standards or reject a batch of products that is actually acceptable. This can lead to quality issues and financial losses. Therefore, it is important to ensure that the sample is random and reflects the characteristics of the population.

Question 3

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?

Accepted Answer

The upper control limit (UCL) for a c-chart is calculated using the formula UCL = $ \bar{c} + 3\sqrt{\bar{c}} $, where $ \bar{c} $ is the average number of complaints per day. For the given data, $ \bar{c} = \frac{3 + 0 + 8 + 9 + 6 + 7 + 4 + 9 + 8}{9} = \frac{54}{9} = 6 $. Thus, UCL = $ 6 + 3\sqrt{6} \approx 6 + 3(2.45) = 6 + 7.35 = 13.35 $.

Question 4

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?

Accepted Answer

The samples show a distinguishable pattern of increasing average diameters, which may indicate a trend or systematic issue in the process.

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

Accepted Answer

A steeper OC curve indicates that there is a larger difference between the acceptance and rejection limits, meaning that it is better at distinguishing between good and bad lots.

Question 7

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)

Accepted Answer

A c-chart is used for counting the number of defects in a single item or service, which is appropriate for measuring defects in hotel room cleaning.

Question 8

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

Accepted Answer

Acceptance sampling involves testing a sample from a larger lot and accepting or rejecting the entire lot based on the results of the sample. Therefore, it is true that acceptance sampling accepts or rejects an entire lot based on the information contained in the sample.

Question 9

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

Accepted Answer

If the mean of the sample falls outside the control limits, it indicates that there is a special or assignable cause of variation present in the process, and it is out of control. The cause of the variation needs to be identified and eliminated to bring the process back to a state of statistical control.

Question 10

Assignable variation

Accepted Answer

Assignable variation is variation that can be traced to a specific cause and needs to be identified and investigated in order to improve the process. It is different from normal or random variation, which is inherent in the process and cannot be eliminated completely. Therefore, B is the best choice as it correctly describes the nature and purpose of assignable variation.

Question 11

Natural variations

Accepted Answer

All of the choices are true. Natural variations affect almost every production process and are the many sources of variation that occur when a process is under control. When grouped, natural variations form a pattern, or distribution, and are tolerated, within limits, when a process is under control.

Question 12

The causes of variation in statistical process control are

Accepted Answer

The two major categories of variation in statistical process control are natural causes and assignable causes. Natural causes refer to random variation that is inherent in the process, while assignable causes refer to specific factors that can be identified and eliminated or controlled in order to improve the process. The other choices refer to specific types of variation or causes that fall under these two major categories.

Question 13

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

Accepted Answer

The x-bar chart is used to monitor the central tendency of a process output, specifically to determine whether there has been a shift in the mean. This is important in detecting and preventing defects, as a shift in the mean may indicate a change in the process that could lead to an increase in defects. The other options are not directly related to the purpose of an x-bar chart.

Question 14

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 can be considered acceptable during random sampling quality inspections. It is not an average level of quality but a threshold.

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?

Accepted Answer

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

Question 16

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 classifying a lot as good or bad and specifies the associated risks for accepting or rejecting each type of lot.

Question 17

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

Accepted Answer

The p-chart is used to monitor the proportion of defectives, or in this case, the proportion of late insurance claim payouts. It is appropriate in situations where the sample size and the probability of a defective item are constant. Therefore, the p-chart is the best choice for measuring the number of late insurance claim payouts per 100.

Question 18

Assignable causes

Accepted Answer

Assignable causes, also known as special causes, are sources of variation that can be identified and eliminated. They are distinct from common causes (or natural causes) of variation, which are inherent to the process.

Question 19

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

Accepted Answer

Acceptance sampling only provides an estimate of the quality of a lot based on the inspection of a sample. It does not guarantee that the entire lot is free of defects.

Question 20

Natural variations

Accepted Answer

Natural variations are inherent in any process and cannot be eliminated completely. As a result, there may be occasional false findings that the process is out of control when it is actually operating within expected natural variations. This is a common challenge in statistical process control. Option A is partially correct but does not capture the fact that natural variations are always present. Option B is incorrect as natural variations are not typically traced to a specific cause. Option C is incorrect as assignable variations are different from natural variations. Option E is incorrect as natural variations have an important role in statistical process control, as they help determine control limits for the process.

Quiz 7: Statistical Process Control

Control charts for variables are based on data that come from

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

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 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?

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

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

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)

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

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

Assignable variation

Natural variations

The causes of variation in statistical process control are

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

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

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?

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

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

Assignable causes

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

Natural variations