SOLUTION: Directional and nondirectional hypotheses can be easily interchanged according to the hypothesis the researcher is testing. For instance, a drug company might predict that a drug w

Question 1117869: Directional and nondirectional hypotheses can be easily interchanged according to the hypothesis the researcher is testing. For instance, a drug company might predict that a drug will help a subject lose weight while another drug company might predict that a drug will alter a subject's weight.
Describe a situation in which you would test a directional hypothesis. Be sure to state the independent variables (e.g., drug or placebo) and the dependent variables (e.g., weight loss) clearly and explain why the hypothesis is directional. Then, revise the same situation to make it nondirectional. Explain which according to you is more appropriate and why. Evaluate the practice of altering the alpha level so that a two-tailed test will have a 5% rejection region on both sides of the curve for a total of 10% instead of having a 2.5% rejection region on both sides in order to maintain a 5% alpha.
Justify your answers with appropriate reasoning and research.

Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
Typically, if one is unaware of the effect a drug will have, a nondirectional study should be used. If one knows it will have a specific effect, one can use a unidirectional study to see how much of an effect is present.
The issue has to do with the critical value. With a significance of 0.05, the test statistic (z) is + 1.64 or -1.64, easier to reach significance, but shouldn't be done if one was not a priori certain of the direction.
For a nondirectional test, the z value would be 1.96, more conservative but fairer should there be no knowledge at the outset as to the direction of the effect.
Making the rejection region 0.05 on either side is essentially allowing a p-value of 0.10, not 0.05. That is not appropriate unless this is in the first stages of a study where one decides that a higher p-value will still be acceptable to move to the second phase.
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