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

Question

Quizplus · Accepted Answer

By switching from a two-tailed test to a one-tailed test, the critical value for rejection becomes less restrictive. Therefore, if the original decision was to reject the null hypothesis, with a one-tailed test in the same direction, we will definitely reject the null hypothesis at α = .05 and perhaps also at α = .01. However, there is still a possibility that we may fail to reject the null hypothesis if the sample size is relatively small or if the effect is weak. Therefore, option A is the best choice.

A Researcher Evaluates a Treatment Effect Using a Two-Tailed Hypothesis