I've often felt that in teaching statistics to psychology (and other social science students) we do them a disservice by teaching one tailed testing. It is a potential point of confusion that does not end up being useful if understood properly. If I could get away with it, I'd avoid teaching it altogether. But, textbooks tend to put such emphasis on the distinction that skipping it would be very confusing to students.
Paul C. Bernhardt Department of Psychology Frostburg State University Frostburg, Maryland -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Fri 1/7/2011 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=13441.4e79e96ebb5671bdb50111f18f263003&n=T&l=tips&o=7744 or send a blank email to leave-7744-13441.4e79e96ebb5671bdb50111f18f263...@fsulist.frostburg.edu --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=7745 or send a blank email to leave-7745-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
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