Hi But one-tailed is used generally (figuratively?) to refer to directional alternative hypotheses (e.g., u1 > u2), and the standard F test is non-directional (i.e., u1>u2 OR u2>u1), even though it only involves (literally) one-tail of the distribution. Assuming only two groups or a single df contrast (e.g., linear), the directional F would have a p of .07/2 = .035.
If you want to have some "fun" with students, try to explain to them why they need to look up the critical value of F for .10 to do a directional (i.e., figurative one-tail) test, although it does help for them to think of the t distribution folded over and that t**2 = F. Take care Jim James M. Clark Professor of Psychology 204-786-9757 204-774-4134 Fax j.cl...@uwinnipeg.ca >>> Marc Carter <marc.car...@bakeru.edu> 07-Jan-11 11:45 AM >>> Ever since one of my grad faculty asked me to do a one-tailed F-test, I hate one-tailed tests. I'm serious -- he really did. The probability of getting the F we got was .07, and he said "Can't you do a one-tailed test?" I explained -- calmly, I believe -- that F *is* effectively a one-tailed test... m -- Marc Carter, PhD Associate Professor and Chair Department of Psychology College of Arts & Sciences Baker University -- > -----Original Message----- > From: Jim Clark [mailto:j.cl...@uwinnipeg.ca] > Sent: Friday, January 07, 2011 11:27 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 > > 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 > j.cl...@uwinnipeg.ca > > >>> "Bourgeois, Dr. Martin" <mbour...@fgcu.edu> 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: sbl...@ubishops.ca [sbl...@ubishops.ca] > 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: mbour...@fgcu.edu. > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=13390.2bbc1cc8fd0e5f9e0b91f0 > 1828c87814&n=T&l=tips&o=7744 > or send a blank email to > leave-7744-13390.2bbc1cc8fd0e5f9e0b91f01828c87...@fsulist.fros > tburg.edu > --- > You are currently subscribed to tips as: j.cl...@uwinnipeg.ca. > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=13251.645f86b5cec4da0a56ffea > 7a891720c9&n=T&l=tips&o=7746 > or send a blank email to > leave-7746-13251.645f86b5cec4da0a56ffea7a89172...@fsulist.fros > tburg.edu > > --- > You are currently subscribed to tips as: marc.car...@bakeru.edu. > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=13029.76c7c563b32ad9d8d09c72 > a2d17c90e1&n=T&l=tips&o=7748 > or send a blank email to > leave-7748-13029.76c7c563b32ad9d8d09c72a2d17c9...@fsulist.fros > tburg.edu > The information contained in this e-mail and any attachments thereto ("e-mail") is sent by Baker University ("BU") and is intended to be confidential and for the use of only the individual or entity named above. 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