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st: RE: RE: one-tailed tests

From   "Airey, David C" <david.airey@Vanderbilt.Edu>
To   "" <>
Subject   st: RE: RE: one-tailed tests
Date   Thu, 8 Jul 2010 16:21:34 -0500


Exactly. We might expect/predict/hope a drug to perform better than a placebo or other gold standard, but we need to be prepared for the drug to do harm. You might want to follow up both possibilities. A directional hypothesis does nothing to prepare you for the other direction. Also, experiments may not be simple, but may allow for complex outcomes (interactions) that may not be easily predicted, but you may wish to follow up either direction for the outcome.

While we are on this topic, there is discussion on the net about differences between a directional hypothesis and the use of one or two tailed tests. They don't seem to be the same thing, exactly.

Here's a fun article on one-tailed tests.

> In some cases, one must make a decision that can be defended legally.  I am thinking about drug approval.  In this case, the FDA wants a two-tailed test (I didn't agree wholly while I was there as I think the theory should tell you the direction), so if it's harmful, they can be very strict on future trials.
> Tony

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