Hi Annette, the name of the procedure you described is "Holm's method", sometimes also referred to as "Bonferroni-Holm"-correction.
There also exists a sequential procedure which starts out with the largest values of p and tests whether comparisons are not significant, called Simes-Hochberg Method, which is even less popular than Bonferroni-Holm. Regards, Rainer Dr. Rainer Scheuchenpflug Lehrstuhl fuer Psychologie III Roentgenring 11 97070 Wuerzburg Tel: 0931-312185 Fax: 0931-312616 Mail: scheuchenpf...@psychologie.uni-wuerzburg.de ---------------------------------------------------------------------------- ----------------------------- Subject: Re: Cross-cultural scientific screw-up, big-time From: <tay...@sandiego.edu> Date: Wed, 7 Jan 2009 15:11:09 -0800 (PST) X-Message-Number: 31 There are various bonferroni procedures you can use if you google them. In one such procedure (darn, the name escapes me!) you simply do the number of post-hoc tests you want as t-tests and then rank order by p-values. You then divide alpha by the total number of comparisons and multiple times the rank order for the critical p. As soon as you fair to exceed critical p you stop and nothing else is considered significant. For example, let's say you are interested in three specific comparisons, you do the t-tests and get the following p-values: .010, .040, .045. If .05 is normally the accepted critical p-value and it is the one you want to use, then you would use the three critical values for comparison to the obtained p-values as (.05/3)*1 = .017. OK, .010 is less than that so the first comparison is considered significant. Next you'd go to (.05/3)*2 = .033 and since you obtained .040 you now reject that one all subsequent comparisons are nonsigificiant. So you don't need the last comparison, which would have given you a comparison of .05. So by controlling for the increased probabiilty of incorrectly finding a significant difference where it is not likely to exist you have now rejected 2 out of the 3 comparisons that you might otherwise have accepted. There really is a name for this procedure but I'm having an old-timer's moment....it will come to me eventually. Of course, all of this presumes you are wedded to the theoretical ideas that underlie traditional significance testing. Annette Annette Kujawski Taylor, Ph.D. Professor of Psychology University of San Diego 5998 Alcala Park San Diego, CA 92110 619-260-4006 tay...@sandiego.edu --- To make changes to your subscription contact: Bill Southerly (bsouthe...@frostburg.edu)
