A quality-control inspector is testing a batch of printed circuit boards to see wheater 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, 2% 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." The manager says that the probability of a type I error must be no larger than 0.01. a. What does a type II error mean here?
b. What is the probability of a type II error?
Here the null hypothesis is that the PCB survives against the alternate that the PCB 'does not survive'. The test says that the PCB will survice if it is classified as 'good'; or, it will not survive if it is classifies as 'bad'.
a. The Type II error is the error committed when a PCB which cannot actually survive is classified as 'good'.
b. Therefore P(Type II error) = P(The PCB is classified as 'good' | PCB does not survives) = 0.03.
