Operations Management - Chapter 10
_______ variation is a variation whose cause can be identified. A. ASSIGNABLE B. Controllable C. Random D. Statistical E. Theoretical
A. Assignable
A control chart used to monitor the fraction of defectives generated by a process is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart
A. p-chart
Studies on a machine that molds plastic water pipe indicate that when it is injecting 1-inch diameter pipe, the process standard deviation is 0.05 inches. The one-inch pipe has a specification of 1-inch plus or minus 0.10 inch. What is the process capability index (Cpk) if the long-run process mean is 1 inch? A. 0.50 B. 0.67 C. 1.00 D. 2.00 E. none of the above
B. 0.67
The specifications for a product are 6 mm ± 0.1 mm. The process is known to operate at a mean of 6.05 with a standard deviation of 0.01 mm. What is the Cpk for this process? A. 3.33 B. 1.67 C. 5.00 D. 2.50 E. none of the above
B. 1.67
A process results in a few defects occurring in each unit of output. Long-run, these defects should be monitored with ___________. A. p-charts B. C-CHARTS C. x-bar charts D. r-charts E. o-charts
B. c-charts
The more effective and all-encompassing a firm's quality control and continuous improvement efforts, the less that company will need to rely on: A. insourcing. B. inspection. C. outsourcing. D. acceptance sampling. E. capability assessment.
B. inspection.
The basis for a statistical process control chart is a (the) __________. A. process capability B. SAMPLING DISTRIBUTION C. control limit D. sample range E. sample mean
B. sampling distribution
A shift in the process mean for a measured characteristic would most likely be detected by a: A. p-chart B. X-BAR CHART C. c-chart D. R-chart E. s-chart
B. x-bar chart
The specification limit for a product is 8 cm and 10 cm. A process that produces the product has a mean of 9.5 cm and a standard deviation of 0.2 cm. What is the process capability, Cpk? A. 3.33 B. 1.67 C. 0.83 D. 2.50 E. none of the above
C. 0.83
A time-ordered plot of sample statistics is called a(n) ______ chart. A. Statistical B. Inspection C. CONTROL D. SIMO E. Limit
C. Control
A time-ordered plot of representative sample statistics is called a: A. Gantt chart B. SIMO-chart C. Control Chart D. Up-Down Matrix E. Standard deviation table
C. Control Chart
If a process is performing as it should, it is still possible to obtain observations which are outside of which limits? (I) tolerances (II) control limits (III) process variability A. I B. II C. I and II D. II and III E. I, II, and III
C. I and II
A plot below the lower control limit on the range chart: (I) should be ignored since lower variation is desirable (II) may be an indication that process variation has decreased (III) should be investigated for assignable cause A. I and II B. I and III C. II and III D. II only E. I, II, and III
C. II and III
Which of the following relationships must always be incorrect? A. Tolerances > process variability > control limits B. Process variability > tolerances > control limits C. Tolerances > control limits > process variability D. Process variability > control limits > tolerances E. Process variability <Tolerances<control limits
C. Tolerances > control limits > process variability
Which of the following is not a step in the quality control process? A. define what is to be controlled B. compare measurements to a standard C. eliminate each of the defects as they are identified D. take corrective action if necessary E. evaluate corrective action
C. eliminate each of the defects as they are identified
The optimum level of inspection occurs when we catch at least 98.6 percent of the defects.
FALSE
The primary purpose of statistical process control is to detect a defective product before it is shipped to a customer.
FALSE
The process capability index (indicated by Cpk) can be used only when the process is centered.
FALSE
The purpose of statistical process control is to ensure that historical output is random.
FALSE
Tolerances represent the control limits we use on the charts.
FALSE
Type I and Type II errors refer to the magnitude of variation from the standard.
FALSE
The greater the capability ratio, the higher the rejects.
FALSE
The larger the process variation, the tighter the specifications should be.
FALSE
The number of defective parts in a sample is an example of variable data because it will "vary" from one sample to another.
FALSE
A point which is outside of the lower control limit on an R-chart: A. is an indication that no cause of variation is present B. should be ignored because it signifies better than average quality C. should be investigated because an assignable cause of variation might be present D. should be ignored unless another point is outside that limit E. is impossible since the lower limit is always zero
C. should be investigated because an assignable cause of variation might be present
A p-chart would be used to monitor _______. A. average shrinkage B. dispersion in sample data C. the fraction defective D. the number of defects per unit E. the range of values
C. the fraction defective
A control chart used to monitor the process mean is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart
C. x-bar chart
When a process is in control, it results in there being, on average, 16 defects per unit of output. C-chart limits of 4 and 28 would lead to a _______ chance of a Type I error. A. 67% B. 92% C. 33% D. 0.3% E. 5%
D. 0.3%
Studies on a bottle-filling machine indicates it fills bottles to a mean of 16 ounces with a standard deviation of 0.10 ounces. What is the process specification, assuming the Cpk index of 1? A. 0.10 ounces B. 0.20 ounces C. 0.30 ounces D. 16.0 ounces plus or minus 0.30 ounces E. none of the above
D. 16.0 ounces plus or minus 0.30 ounces
The probability of concluding that assignable variation exists when only random variation is present is: (I) the probability of a Type I error (II) known as the alpha risk (III) highly unlikely (IV) the sum of probabilities in the two tails of the normal distribution A. I and II B. I and IV C. II and III D. I, II, and IV E. I, III, and IV
D. I, II, and IV
A control chart used to monitor the number of defects per unit is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart
D. c-chart
The purpose of control charts is to: A. estimate the proportion of output that is acceptable B. weed out defective items C. determine if the output is within tolerances/specifications D. distinguish between random variation and assignable variation in the process E. provide meaningful work for quality inspectors
D. distinguish between random variation and assignable variation in the process.
The optimum level of inspection is where the: A. cost of inspection is minimum B. cost of passing defectives is minimum C. total cost of inspection and defectives is maximum D. total cost of inspection and defectives is MINIMUM E. difference between inspection and defectives costs is minimum
D. total cost of inspection and defectives is minimum
Organizations should work to improve process capability so that quality control efforts can become more ________. A. effective B. efficient C. necessary D. UNNECESSARY E. widespread
D. unnecessary
The range chart (R-chart) is most likely to detect a change in: A. proportion B. mean C. number defective D. VARIABILITY E. sample size
D. variability
When a process is in control, it results in there being, on average, 16 defects per unit of output. C-chart limits of 8 and 24 would lead to a _______ chance of a Type I error. A. 67% B. 92% C. 33% D. .03% E. 5%
E. 5%
The process capability index (Cpk) may mislead if: (I) the process is not stable. (II) the process output is not normally distributed. (III) the process is not centered. A. I and II B. I and III C. II and III D. II only E. I, II and III
E. I, II and III
Inspection is a(n): A. prevention. B. control. C. monitoring. D. corrective. E. appraisal.
E. appraisal.
Quality control, in contrast to quality assurance, is implemented: A. after production. B. before inspection. C. by self-directed teams. D. by top management. E. during production.
E. during production.
A c-chart is used for: A. means B. ranges C. percent defective D. fraction defective per unit E. number of defects per unit
E. number of defects per unit
Which of the following quality control sample statistics indicates a quality characteristic that is an attribute? A. mean B. variance C. standard deviation D. range E. proportion
E. proportion
A c-chart is used to monitor the total number of defectives in the output of a process.
FALSE
A process that exhibits random variability would be judged to be out of control.
FALSE
An "up and down" run test uses the median as a reference point and measures the percentage above and below the median.
FALSE
An R value of zero (on a range chart) means that the process must be in control since all sample values are equal.
FALSE
An x-bar control chart can only be valid if the underlying population it measures is a normal distribution.
FALSE
Approving the effort that occurs during the production process is known as acceptance sampling.
FALSE
Approximately 99.7% of sample means will fall within ± two standard deviations of the process mean if the process is under control.
FALSE
Attributes need to be measured, variable data can be counted.
FALSE
Control limits are based on multiples of the process standard deviation.
FALSE
Control limits used on process control charts are specifications established by design or customers.
FALSE
Even if the process is not centered, the process capability index (indicated by Cpk) is very useful.
FALSE
Larger samples will require wider x-bar control limits because there is more data.
FALSE
Low-cost, high-volume items often require more intensive inspection.
FALSE
Non-random variation is likely whenever all observations are between the LCL and UCL.
FALSE
Processes that are in control eliminate variations.
FALSE
Range charts and p-charts are both used for variable data.
FALSE
Range charts are used mainly with attribute data.
FALSE
Range control charts are used to monitor process central tendency.
FALSE
Run tests give managers an alternative to control charts; they are quicker and cost less.
FALSE
Statistical Process Control is the measurement of rejects in the final product.
FALSE
Statistical process control focuses on the acceptability of process output.
FALSE
The Taguchi Cost Function suggests that the capability ratio can be improved by extending the spread between LCL and UCL.
FALSE
The best way to assure quality is to use extensive inspection and control charts.
FALSE
"Assignable variation" is variation due to a specific cause, such as tool wear.
TRUE
"Process capability" compares "process variability" to the "tolerances."
TRUE
"Quality of conformance" is concerned with whether a product or service conforms to its specifications.
TRUE
A c-chart is used to monitor the number of defects per unit for process output.
TRUE
A lower control limit must by definition be a value less than an upper control limit.
TRUE
A p-chart is used to monitor the fraction of defectives in the output of a process.
TRUE
A run test checks a sequence of observations for randomness.
TRUE
Attribute data are counted, variable data are measured.
TRUE
Concluding a process is out of control when it is not is known as a Type I error.
TRUE
Control limits tend to be wider for more variable processes.
TRUE
High-cost, low-volume items often require careful inspection since we make them so infrequently.
TRUE
If a point on a control chart falls outside one of the control limits, this suggests that the process output is non-random and should be investigated.
TRUE
Patterns of data on a control chart suggest that the process may have non-random variation.
TRUE
Quality control is assuring that processes are performing in an acceptable manner.
TRUE
Run tests are useful in helping to identify nonrandom variations in a process.
TRUE
The amount of inspection needed is governed by the costs of inspection and the expected costs of passing defective items.
TRUE
The amount of inspection we choose can range from no inspection at all to inspecting each item numerous times.
TRUE
The optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.
TRUE
The output of a process may not conform to specifications even though the process may be statistically "in control."
TRUE
The sampling distribution can be assumed to be approximately normal even when the underlying process distribution is not normally distributed.
TRUE
The variation of a sampling distribution is tighter than the variation of the underlying process distribution.
TRUE
Variation in a sample statistic collected from a process may be either random variation or assignable variation - or both.
TRUE
When a process is not centered, its capability is measured in a slightly different way. The symbol for this case is Cpk.
TRUE
