chapter 16

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University of Texas, Permian Basin *

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6301

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Statistics

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Feb 20, 2024

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docx

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CHAPTER 16 1. Which of the following control charts is based on the number of defects within a sample? c 2. Which of the following control charts is used to monitor the number of defective items within a sample? p 3. If the quality of a process's output is determined by the number of defects within a small sample, use a(n) ?? control chart c 4. If the quality of a process's output is determined by classifying the output as being defective or not defective, use a(n) ?? control chart. p 5. Which of the following control charts are based on sample sizes as small as one? c 6. Which of the following control charts are often based on sample sizes larger than one hundred? p 7. Which of the following charts are frequently used together to monitor and control quality? R/x Bar 8. Which of the following control charts is used to control the variation BETWEEN samples? x-bar 9. If the quality of a process's output is determined by the difference between the largest and smallest values in a sample, use a(n) ?? control chart. R 10. If the quality of a process's output is determined by the average value of a sample, use a(n) ?? control chart. x-bar 11. Which of the following charts is used to control variation WITHIN samples R 12. Statistical process control involves monitoring and controlling a process to prevent poor quality. Ans: True, 13. Statistical process control is based on a philosophy of inspection as opposed to prevention. 14. Ans: False 15. One goal of statistical process control is to prevent a process from producing items that have to be scrapped or reworked Ans: True 16. Two types of variation associated with the output of a process are common cause (random) and special cause (nonrandom). 1

CHAPTER 16 Ans: True 17. Control limits are based on the special cause (nonrandom) variation inherent in a process. Ans: False 18. A process that is determined to be in control contains no variation. Ans: False 19. Common cause (random) variation provides evidence that the process is not in control. Ans: False 20. After special cause variation is detected, the focus changes to identifying the root cause of the variation and eliminating it. Ans: True 21. Process control is achieved by taking periodic samples from a process and plotting the sample points on a chart to determine if the process is within control limits. Ans: True 22. When a control chart detects no special cause (nonrandom) variation in a process, the upper and lower control limits are the same value. Ans: False 23. It is sometimes not necessary to determine new control limits after special cause (nonrandom) variation has been identified if the source has been eliminated without changing the process. Ans: True 24. A variable measure classifies while an attribute measure quantifies. Ans: False 25. With a c-chart, the sample size is small and may contain only one item. Ans: True 26. A p-chart is used to monitor the proportion defective in the output of a process. Ans: True 27. Attribute control charts are used to monitor descriptive characteristics of the output of a process rather than measurable characteristics. Ans: True 28. The formula used to determine the upper and lower control limits are based on product specification limits. Ans: False 2

CHAPTER 16 29. Variable control charts are used to monitor measurable characteristics of a process's outputs rather than descriptive characteristics. Ans: True 30. An x-bar and R-chart constructed to monitor and control a process use the same raw data. Ans: True 31. Variable control charts are used for quantitative measures such as weight or time. Ans: True 32. Construction and use of an -chart is based on an assumption that the sample points are normally distributed around the centerline. Ans: True 33. The range is the difference between the smallest and largest values in a sample. Ans: True 34. The range measures the variation within samples versus the variation between samples. Ans: True, 35. It is possible to have low variation within samples while at the same time having high variation between sample means. Ans: True 36. One advantage of using a pattern test is that special cause variations may be identified before any points are plotted outside the control limits. Ans: True 37. A pattern test can identify an out-of-control process even if all sample points are within control limits. Ans: True, 38. A control chart is in control when the plot of the sample points exhibits a pattern. Ans: False 39. If the points plotted on a control chart display a pattern, it is called a run. Ans: True 40. When constructing a control chart for the first time, all points should be within the control limits indicating the process is in control. 3

CHAPTER 16 Ans: True 41. Process control charts are often used at a critical point after which it is difficult to correct or rework the process output. Ans: True, 42. Control charts visually show when a process is not within statistical control limits. Ans: True 43. The popularity of Excel and other data analysis software has been a major factor in the increased use of statistical process control. Ans: True 44. Tolerances or specification limits are allowable variation prescribed in a product design. Ans: True 45. Tolerances reflect the amount of common cause variation allowed in a process. Ans: False 46. For a given process, the process capability ratio is not related to its specification limits. Ans: False 47. A process capability ratio greater than one shows that a process is capable of producing output within its specification limits. Ans: True 48. All processes contain a certain amount of variation in their output. Ans: True 49. A sequence of sample points that display a pattern is known as a run. Ans: True 50. Statistical process control can prevent poor quality before it occurs if a pattern is evident in the plotted points. Ans: True 51. The process capability index indicates how much a process mean differs from the target specification value. Ans: True 52. If a sample point plotted on a control chart is outside the control limits a. the evidence indicates the process is in control. b. the evidence indicates the process is out of control. c. the evidence is inconclusive. 4

CHAPTER 16 d. None of these answer choices is correct. b 53. Which of the following could be responsible for variability that is special cause (nonrandom)? a. Broken machinery. b. Defective parts and materials. c. Operator error. d. All these answer choices are correct. d 54. Common (random) variation of a process depends on all the following except a. errors due to lack of training. b. the equipment and machinery used. c. the operator. d. system used for measurement. a 55. An attribute measure is a product characteristic such a. weight. b. color. c. length. d. time b 56. A variable measure is a product characteristic such as a. color. b. smooth. c. temperature d. tastes good c 57. Which of the following services can be measured and monitored with control charts? a. Hospitals b. Airlines c. Banks d. All these answer choices are correct D 58. Control charts are typically used at the ___________ of a process. a. beginning. b. middle. c. end. d. All these answer choices are correct. a 5

CHAPTER 16 59. Which of the following is not a primary purpose of statistical process control? a. to establish control limits b. to detect special cause variations c. to identify specification limits d. to determine when a process is not in control c 60. Four common types of control charts include all of the following except: a. -chart b. t-chart c. p-chart d. c-chart b 61. Which of the following is not a characteristic of a control chart? a. the centerline is determined using special cause (nonrandom) variations. b. the upper and lower control limits are based on special cause (nonrandom) variation. c. the centerline is determined by using the target value. d. None of these answer choices is correct. d 62. Special cause (nonrandom) variation in a process is more likely to be detected with a. wider control limits b. narrow control limits c. wider specification limits d. narrow specification limits b 63. Which of the following statements concerning control chart limits is true? a. the smaller the value of z, the more narrow the control limits are and the more sensitive the chart is to changes in the production process b. the larger the value of z, the more narrow the control limits are and the more sensitive the chart is to changes in the production process c. the smaller the value of z, the wider the control limits are and the less sensitive the chart is to changes in the production process d. the larger the value of z, the more narrow the control limits are and the less sensitive the chart is to changes in the production process a 6

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