9-29. A quality-control inspector is testing a batch of printed circuit boards t
ID: 3291908 • Letter: 9
Question
9-29. A quality-control inspector is testing a batch of printed circuit boards to see whether they are capable of performing in a high temperature environment. He knows that the boards that will survive will pass all five of the tests with probability 98%. They will pass at least four tests with probability 99%, and they always pass at least three. On the other hand, the boards that will not survive sometimes pass the tests as well. In fact, 3% pass all five tests, and another 20% pass exactly four. The rest pass at most three tests. The inspector decides that if a board passes all five tests, he will classify it as “good.” Otherwise, he’ll classify it as “bad.”
(a) What does a type I error mean in this context?
(b) What is the probability of a type I error?
(c) What does a type II error mean here?
(d) What is the probability of a type II error?
9-30. In the quality-control example of Exercise 9-29, the manager says that the probability of a type I error is too large and that it must be no larger than 0.01.
(a) How does this change the rule for deciding whether a board is “good”?
(b) How does this affect the type II error?
(c) Do you think this reduction in type I error is justified? Explain briefly.
Explanation / Answer
Solution:
a) type one error means rejecting a good board (classifying it as a bad board).
b)Probability 1-.98=.02
c) Failing to reject a board when it is in fact bad (classifying it as a good board)
d) Probability .03
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