MULTIPLE CHOICE
1. If a sample of items is taken and the mean of the sample is outside the control limits the process is
1.a. out of control and the cause should be established
2.b. in control, but not capable of producing within the established control limits
3.c. within the established control limits with only natural causes of variation
4.d. monitored closely to see if the next sample mean will also fall outside the control limits
5.e. producing high quality products
2. The causes of variation in statistical process control are
1.a. cycles, trends, seasonality, and random variations
2.b. producer's causes and consumer's causes
3.c. mean and range
4.d. natural causes and assignable causes
5.e. Type I and Type II
3. Natural variations
1.a. affect almost every production process
2.b. are the many sources of variation that occur when a process is under control
3.c. when grouped, form a pattern, or distribution
4.d. are tolerated, within limits, when a process is under control
5.e. All of the above are true.
4. Natural variations
1.a. are variations that are to be identified and eliminated
2.b. are variations that can be traced to a specific cause
3.c. are the same as assignable variations
4.d. lead to occasional false findings that processes are out of control
5.e. play no role in statistical process control
5. Assignable variation
1.a. is a sign that a process is under control
2.b. is to be identified and eliminated
3.c. is the same as random variation
4.d. is variation that cannot be traced to a specific cause
5.e. leads to a steep OC curve
6. Assignable causes
1.a. are not as important as natural causes
2.b. are within the limits of a control chart
3.c. depend on the inspector assigned to the job
4.d. are also referred to as "chance" causes
5.e. are causes of variation that can be identified and removed
7.Control charts for variables are based on data that come from
1.a. acceptance sampling
2.b.individual items
3.c.averages of small samples
4.d.averages of large samples
5.e.the entire lot
8.The purpose of an X chart is to determine whether there has been a
1.a.gain or loss in uniformity
2.b.change in the percent defective in a sample
3.c.change in the central tendency of the process output
4.d.change in the number of defects in a sample
5.e. change in the AOQ
9.Statistical process control charts
1.a. display the measurements on every item being produced
2.b. display upper and lower limits for process variables or attributes, and signal when a process is no longer in control
3.c. indicate to the process operator the average outgoing quality of each lot
4.d.indicate to the operator the true quality of material leaving the process
5.e.none of the above
10.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?
1.a. The process is out of control, and the cause should be established.
2.b. The process is in control, but not capable of producing within the established control limits.
3.c. The process is within the established control limits with only natural causes of variation.
4.d. The process is outside the established control limits with only natural causes of variation.
5.e. The process is in control, and there is nothing to worry about.
11.The Central Limit Theorem
1.a.is the theoretical foundation of the c-chart
2.b.states that the average of assignable variations is zero
3.c.allows managers to use the normal distribution as the basis for building some control charts
4.d.states that the average range can be used as a proxy for the standard deviation
5.e.controls the steepness of an operating characteristic curve
12.For an x-bar chart where the standard deviation is known, the Upper Control Limit
1.a. is 3⋅σ below the mean of sample means for a 3σ control chart
2.b. is 3⋅σ above the mean of sample means for a 3σ control chart
3.c. is 3⋅σ n below the mean of sample means for a 3σ control chart
4.d. is 3⋅σ n above the mean of sample means for a 3σ control chart
5.e. cannot be calculated unless the average range is known
13.Up to three standard deviations above or below the centerline is the amount of variation that statistical process control allows for
1.a. Type I errors
2.b. about 95.5% variation
3.c. natural variation
4.d. all types of variation
5.e. assignable variation
14.A manager wants to build 3σ 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
1.a. -8 and 28
2.b. 16 and 4
3. c. 12 and 8
4.d. 4 and 16
5.e. 8 and 12
15.The type of inspection that classifies items as being either good or defective is
1. a. variable inspection
2.b. attribute inspection
3.c. fixed inspection
4.d. all of the above
5.e. none of the above
16.The x-bar chart tells us whether there has been a
1.a. gain or loss in dispersion
2.b. change in the percent defective in a sample
3.c. change in the central tendency of the process output
4.d. change in the number of defects in a sample
5.e. none of the above
17.The mean and standard deviation for a process for which we have a substantial history are x = 120 and σ = 2. For the variable control chart, a sample size of 16 will be used. What is the mean of the sampling distribution?
1. a. 1/8 (0.125)
2. b. 0.5
3. c. 2
4.d. 40
5.e. none of the above
18.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?
1.a. p-charts
2.b. c-charts
3.c. x-and R-charts
4.d. x-, but not R-charts
5.e. both p- and c-charts