On 13 Jan 2009 at 16:52, Paul C Bernhardt wrote: >> Presumably, doing worse than chance would be meaningless. Out of the 280 > trials provided by the practitioners, they guessed correctly 123 times, 44%. > Obviously, this was a result in the opposite direction of the one tailed > test and is not meaningful. > > Or is it? > > Turns out that 123 hits out of 280 attempts just breaks below a .05 two > tailed test of significance by a binomial test. Hmmm....
This is a wonderfully instructive case. I love it. It certainly argues in favour of extreme caution before declaring that one has absolutely no interest in a result falling in a particular tail (which would then justify a one-tailed test). Because just sometimes, that's where those obstreperous chips nonetheless fall, and what do you do then? Thanks, Paul. And while we're on the subject, I'll go out on a limb here. In 99.9% of the cases (maybe higher), when you see a one-tailed test in the literature, it's for one of two reasons: 1) The user believes, incorrectly, that all you need is a directional hypothesis to justify its use 2) It wasn't significant with a two-tailed test. Stephen ----------------------------------------------------------------- Stephen L. Black, Ph.D. Professor of Psychology, Emeritus Bishop's University e-mail: [email protected] 2600 College St. Sherbrooke QC J1M 1Z7 Canada Subscribe to discussion list (TIPS) for the teaching of psychology at http://flightline.highline.edu/sfrantz/tips/ ----------------------------------------------------------------------- --- To make changes to your subscription contact: Bill Southerly ([email protected])
