When to use one tailed or two tailed tests for power analysis?

Asked May 03 '20 at 02:07

Active Oct 05 '21 at 14:39

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Is it ok to choose one tailed test if it is assumed that a certain drug is going to reduce metastatic tumor?

edited Oct 05 '21 at 14:39

asked May 03 '20 at 02:07

Lily

2

At the start, everyone involved _hopes_ that a new drug will have a desired effect in the appropriate direction. Unfortunately, some drugs actually have a contrary effect. In most countries, trials for approval of a drug must follow protocols approved in advance by gov't agencies as to 1 or 2-sidedness and methods of analysis. So the final word on this is not up to the experimenter but up to a gov't agency. // One-sided tests typically require fewer subjects to get a given power, so it is legitimate to try getting 1-sided tests into the protocol, but there is no guarantee of approval. – BruceET May 03 '20 at 03:08

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