SOLUTION: Discuss one-sample test of hypothesis. Include an explanation of the following: 1. In hypothesis testing when is a two-tail test used in lieu of a one-tail test and why? 2. In hypo

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Question 1073051: Discuss one-sample test of hypothesis. Include an explanation of the following: 1. In hypothesis testing when is a two-tail test used in lieu of a one-tail test and why? 2. In hypothesis testing when is the "t test" used rather than the "Z test"?
Answer by Boreal(15235) About Me  (Show Source):
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One uses a 2-tail test to look for a difference in either direction, which is in general a better test and more difficult to reach the level of significance. A one-tail test shows a difference with more power, but it should only be done when there is very high likelihood that one will find a priori a directional difference.
One uses a t-test when a sample is used and the variance of the sample is considered an adequate estimation of the variance of the population from which the sample is taken. Both tests require an assumption of normality and random samples.