Statistical Methods for Quality Improvement, Third Edition

Answers to Selected Exercises

Chapter 2

• 1. 9

Chapter 3

• 1. S² = 7.3. Adding a constant to every number in a sample does not change the value of S².
• 5. (a) 0.95053; (d) 0.9545; (e) z₀ = 1.96.
• 7. .
• 9. 0.06681. The probability is approximate since the particular probability distribution was not stated.
• 15. 2. We have 3% as the estimate of the proportion nonconforming, and conclude that the process needs improving.
• 17. 0.9727.
• 22. (c)

Chapter 4

• 5. The control limits could be adjusted or a control chart of residuals could be used.
• 20. 80.5

Chapter 5

• 2. 13, 2.
• 3. The moving ranges and moving averages are correlated so interpreting the charts can be difficult.
• 5. An chart is more sensitive in detecting a shift in the process mean (as the answers to exercise 2 indicate).

Chapter 6

• 1. 0.0462 and 0.2583.
• 3. Because there will not be a lower control limit.

Chapter 7

• 3. (a) ; (c) decrease, 0.02278 (before), 0.0027 (after).
• 5. 1.479, no.

Chapter 8

• 2. (a) 5.75 assuming a basic CUSUM scheme; (b) 15.
• 3. When doubt exists as to whether or not an assignable cause was removed.

Chapter 9

• 1. (a) 11.58.

Chapter 11

• 2. (a) No outliers are identified; (b) the estimate of sigma is 3.21.

Chapter ...