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ISDS 3115 Chapter S6
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Gravity
Chapter S6
Terms in this set (49)
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
a. out of control and the cause should be established;
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
d. natural causes and assignable causes
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.
e. All of the above are true.
Natural causes
a. are variations that are to be identified and eliminated
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
d. lead to occasional false findings that processes are out of control
Assignable variation
a. is a sign that a process is under control
b. is to be identified and eliminated
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
b. is to be identified and eliminated
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 removed
e. are causes of variation that can be identified and removed
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
c. averages of small samples
The purpose of an X chart is to determine whether there has been a
a. gain or loss in uniformity
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
c. change in the central tendency of the process output
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
b. display upper and lower limits for process variables or attributes, and signal when a process is
A sample of parts is measured. The mean of this sample is in the middle of the control limits, but
some individual parts measure too low for design specifications and other parts measure too high.
Which of the following is true?
a. The process is out of control, and the cause should be established.
b. The process is in control, but not capable of producing within the established control limits.
c. The process is within the established control limits with only natural causes of variation.
d. The process is outside the established control limits with only natural causes of variation.
e. The process is in control, and there is nothing to worry about.
b. The process is in control, but not capable of producing within the established control limits.
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
c. allows managers to use the normal distribution as the basis for building some control charts
For an x-bar chart where the standard deviation is known, the Upper Control Limit
a. is 3below the mean of sample means for a 3 control chart
b. is 3 above the mean of sample means for a 3 control chart
c. is 3 n below the mean of sample means for a 3 control chart
d. is 3 n above the mean of sample means for a 3 control chart
e. cannot be calculated unless the average range is known
d. is 3 n above the mean of sample means for a 3 control chart
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
c. natural variation
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
b. attribute inspection
The x-bar 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
c. change in the central tendency of the process output
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. x - and R-charts
d. x -, but not R-charts
e. both p- and c-charts
c. x - and R-charts
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
a. gain or loss in dispersion
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.; e. Variation is not in control; investigate what created this condition.
To set x -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
a. average of the sample means
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
c. ± 3 standard deviations
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 may be below zero.
d. The lower control limit may be at zero.
e. The lower control limit is the same as the lot tolerance percent defective.
d. The lower control limit may be at zero.
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
c. process sampling by attributes
The statistical process chart used to control the number of defects per unit of output is the
a. x -chart
b. R-chart
c. p-chart
d. AOQ chart
e c-chart
e c-chart
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
b. change in the number of defects per unit
The local newspaper receives several complaints per day about typographic errors. Over a sevenday
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. x -chart
d. R-chart
e. x - and R-charts
b. c-chart
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
b. p-chart for A, c-chart for B
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. x - and R-charts
b. p-charts
c. c-charts
d. x -, but not R-charts
e. both p- and c-charts
c. c-charts
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
d. to examine points in a control chart to check for nonrandom variability
Which of the following is true regarding the process capability index Cpk?
a. A Cpk index value of 1 is ideal, meaning all units meet specifications.
b. The larger the Cpk, the more units meet specifications.
c. The Cpk index can only be used when the process centerline is also the specification centerline.
d. Positive values of the Cpk index are good
negative values are bad.
e. None of the above is true.; b. The larger the Cpk, the more units meet specifications.
If the Cpk index exceeds 1
a. the AQL must be smaller than the LTPD
b. must be less than one-third of the difference between the 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"
b. must be less than one-third of the difference between the specification and the process mean
The statistical definition of Six Sigma allows for 3.4 defects per million. This is achieved by a Cpk
index of
a. 0
b. 1
c. 1.33
d. 1.67
e. 2
e. 2
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
c. is used to determine whether to accept or reject a lot of material based on the evaluation of a sample
Acceptance sampling's primary purpose is to
a. estimate process quality
b. estimate lot quality
c. detect and eliminate defectives
d. decide if a lot meets predetermined standards
e. determine whether defective items found in sampling should be replaced
d. decide if a lot meets predetermined standards
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
d. an operating characteristics curve
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.
e. All of the above are true.
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.
d. All of the above are true.
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
d. incoming lots of purchased products
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
d. how well an acceptance sampling plan discriminates between good and bad lots
An operating characteristics curve shows
a. upper and lower product specifications
b. product quality under different manufacturing conditions
c. how the probability of accepting a lot varies with the population percent defective
d. when product specifications don't match process control limits
e. how operations affect certain characteristics of a product
c. how the probability of accepting a lot varies with the population percent defective
Producer'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
b. rejecting a good lot
Which of the following is true regarding the relationship between AOQ and the true population
percent defective?
a. AOQ is greater than the true percent defective.
b. AOQ is the same as the true percent defective.
c. AOQ is less than the true percent defective.
d. There is no relationship between AOQ and the true percent defective.
e. The relationship between these two cannot be determined.
c. AOQ is less than the true percent defective.
Average outgoing quality (AOQ) usually
a. worsens with inspection
b. stays the same with inspection
c. improves with inspection
d. may either improve or worsen with inspection
e. is the average quality before inspection
c. improves with inspection
A Type I error occurs when
a. a good lot is rejected
b. a bad lot is accepted
c. the number of defectives is very large
d. the population is worse than the AQL
e. none of the above
a. a good lot is rejected
A Type II error occurs when
a. a good lot is rejected
b. a bad lot is accepted
c. the population is worse than the LTPD
d. the proportion of defectives is very small
e. none of the above
b. a bad lot is accepted
In most acceptance sampling plans, when a lot is rejected, the entire lot is inspected and all defective items are replaced. When using this technique the AOQ
a. worsens (AOQ becomes a larger fraction)
b. improves (AOQ becomes a smaller fraction)
c. is not affected, but the AQL is improved
d. is not affected
e. falls to zero
b. improves (AOQ becomes a smaller fraction)
An acceptance sampling plan is to be designed to meet the organization's targets for product quality
and risk levels. Which of the following is true?
a. n and c determine the AQL.
b. AQL, LTPD, and collectively determine n and c.
c. n and c are determined from the values of AQL and LTPD.
d. and are determined from the values of AQL and LTPD.
e. None of the above is true.
b. AQL, LTPD, and collectively determine n and c
A lot that is accepted by acceptance sampling
a. has more defects than existed before the sampling
b. has had all its defects removed by 100% inspection
c. will have the same defect percentage as the LTPD
d. has no defects present
e. All of the above are false.
e. All of the above are false.
Which of the following statements about acceptance sampling is true?
a. The steeper an OC curve, the better it discriminates between good and bad lots.
b. Acceptance sampling removes all defective items.
c. Acceptance sampling of incoming lots is replacing statistical process control at the supplier.
d. Acceptance sampling occurs continuously along the assembly line.
e. All of the above are true.
a. The steeper an OC curve, the better it discriminates between good and bad lots.
Which of the following is true regarding the average outgoing quality level?
a. An AOQ value of 1 is ideal, because all defects have been removed.
b. AOQ is always greater than AQL but less than LTPD.
c. AOQ rises (worsens) following inspection of failed lots.
d. AOQ is very low (very good) for extremely poor quality lots.
e. None of the above is true.
d. AOQ is very low (very good) for extremely poor quality lots.
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