Wuzzy, I feel contrasts, in general, are important. You seem aware of the "cell means" approach. For example, in a 2x3 factorial you can test the full model using the usual ANOVA table (with interactions). Or, you can specify 6 means and do an "omnibus" test (5 df). The planned comparisons using these 5 df would be something like this
(A main effects) 1 1 1 -1 -1 -1 (B main effects) 1 -1 0 1 -1 0 1 0 -1 1 0 -1 (AxB interactions) 1 -1 0 -1 1 0 1 0 -1 -1 0 1 5 contrasts...5 df...globally test all of these for the usual ANOVA omnibus test. Warren [EMAIL PROTECTED] (wuzzy) wrote in message news:<[EMAIL PROTECTED]>... > Has anyone come across an intro on planned contrasts. > I suppose a background in algebra is required to teach vector-space > contrasts. I've also seen multiple regression taught in terms of > vector-space and matrix algebra. Are contrasts considered important > to teach for experimental design, > any recommended texts? eg., the argument could be made that omnibus > tests are sufficient. > Usually I don't see the term "planned contrast" in non-statistical > literature, maybe I just haven't been aware of it. > -wuzzy . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
