A researcher evaluates a treatment effect using a two-tailed hypothesis test with $\alpha$ = .05,and the decision is to reject the null hypothesis.If the researcher switched to a one-tailed test using the same sample,what decision would be made?
A)Definitely reject the null hypothesis with $\alpha$ = .05 and maybe reject with $\alpha$ = .01
B)Definitely reject the null hypothesis with $\alpha$ = .05 and with $\alpha$= .01
C)Definitely fail to reject the null hypothesis with either $\alpha$= .05 or with $\alpha$ = .01
D)It is impossible to predict the outcome of the one-tailed test.

Question

Quizplus · Accepted Answer

Switching from a two-tailed test to a one-tailed test increases the power of the test, but also narrows the critical region. Therefore, the decision to reject the null hypothesis in a two-tailed test may not necessarily translate to a rejection in a one-tailed test, as the significance level may be different. It is possible that the null hypothesis may still stand with a one-tailed test, especially if the significance level is lowered to .01. Thus, the best choice is A, which acknowledges this possibility and states that a rejection is definite with .05 significance level but only a maybe with the lowered .01 significance level.

A Researcher Evaluates a Treatment Effect Using a Two-Tailed Hypothesis α\alphaα

A Researcher Evaluates a Treatment Effect Using a Two-Tailed Hypothesis $\alpha$