Hi I think of one-tailed (or Abelson's 1.5 tailed) tests as a kind of quasi-bayesian adjustment to the standard non-directional test. That is, given empirical or theoretical grounds for expecting an outcome in one direction, then one needs less evidence from the present study before moving in that direction. I also sometimes use a perceptual metaphor ... primed to expect some stimulus (e.g., meeting someone in a crowded room), one needs less perceptual input before identifying the person.
Also, it would appear that the same issues would arise with planned versus post hoc comparisons. That is, post hoc requires some adjustment for multiple tests, whereas planned may not because of the expectation of a predicted pattern. Take care Jim James M. Clark Professor of Psychology 204-786-9757 204-774-4134 Fax [email protected] >>> "Bourgeois, Dr. Martin" <[email protected]> 07-Jan-11 11:06 AM >>> Robert Abelson, in his excellent book Statistics as Principled Argument, advocates the use of what he calls a one-and-a-half tailed test for directional predictions; for example, you could set the alpha level at .04 in the tail of the predicted direction and .01 in the unpredicted direction. I always thought that was a neat idea, but I've never seen anyone use it. ________________________________________ From: [email protected] [[email protected]] Sent: Friday, January 07, 2011 11:04 AM To: Teaching in the Psychological Sciences (TIPS) Subject: Re: [tips] Don't Be Surprised If Your Physics Colleagues Snicker When They Pass You In the Hall On 6 Jan 2011, I wrote in response to Martin Bourgeois pointing out that Bem used one-tailed tests: > That's interesting, disturbing, in fact. I've long argued that one- > tailed tests are almost uniformly misused in psychology and should be > banned. Making a one-sided prediction is insufficient justification. > One should only be allowed to use a one-tailed test if one can > plausibly argue that not only do I not predict a result in the > "wrong" tail, but that if such a perverse result occurred, it would > either be meaningless or of no interest at all. I am happy to report that a paper hot off the press (or do they not do that any more?), in what appears to be a brand-new journal, has an excellent opinion piece which fully supports my view above. How they got it into print so quickly after reading my post, I'll never know. The paper is this: Ruxton, G, and Neuhauser, M. (2010). When should we use one-tailed hypothesis testing? Methods in Ecology and Evolution, 1, 114-117. After giving a great example of the tangled mess an unwary researcher is faced with when a one-tailed test goes rogue, they say this: "On the basis of their statistical test, the scientist has no grounds for treating an experiment where the birds having a spectacular adverse reaction to the supplement any differently from the birds having no reaction. This philosophical lack of ability to act in response to unexpected results is the cost of one-tailed testing". Amen! Cut your costs! Help stamp out one-tailed tests! They also say "We rarely find ourselves in a position where we are comfortable with using a one-tailed test", and later, "Use of one- tailed testing is more common than we would expect" [in ecology journals], They report that none of these uses involved a satisfactory explanation. The authors' summary, in modest and restrained language, offers this good guide for the perplexed: ---------------------------- Summary 1. Although one-tailed hypothesis tests are commonly used, clear justification for why this approach is used is often missing frompublished papers. 2. Here we suggest explicit questions authors should ask of themselves when deciding whether or not to adopt one-tailed tests. 3. First, we suggest that authors should only use a one-tailed test if they can explain why they are more interested in an effect in one direction and not the other. 4. We suggest a further requirement that adoption of one-tailed testing requires an explanation why the authors would treat a large observed difference in the unexpected direction no differently from a difference in the expected direction that was not strong enough to justify rejection of the null hypothesis. 5. These justifications should be included in published works that use one-tailed tests, allowing editors, reviewers and readers the ability to evaluate the appropriateness of the adoption of one-tailed testing. 6. We feel that adherence to our suggestions will allow authors to use one-tailed tests more appropriately, and readers to form their own opinion about such appropriateness when one-tailed tests are used. ------------------------- Stephen -------------------------------------------- Stephen L. Black, Ph.D. Professor of Psychology, Emeritus Bishop's University Sherbrooke, Quebec, Canada e-mail: sblack at ubishops.ca --------------------------------------------- --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13390.2bbc1cc8fd0e5f9e0b91f01828c87814&n=T&l=tips&o=7744 or send a blank email to leave-7744-13390.2bbc1cc8fd0e5f9e0b91f01828c87...@fsulist.frostburg.edu --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13251.645f86b5cec4da0a56ffea7a891720c9&n=T&l=tips&o=7746 or send a blank email to leave-7746-13251.645f86b5cec4da0a56ffea7a89172...@fsulist.frostburg.edu --- You are currently subscribed to tips as: [email protected]. 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