Depends partly on why you have three control groups. If they were thought to be equivalent, or exchangeable, it would probably be efficient to pool them into a single group. If they are not (e.g., if each control group is "controlling" for a different thing), will you be interested in differences between the several controls? (If so, this would argue against Dunnett's test, since not all the comparisons of interest are of that kind. But if you are indifferent to whatever differences may exist between control groups, and pairwise comparisons involving your one experimental group are your ONLY interest, Dunnett's would seem appropriate.)
don raises a conceptual point ... if you have 3 controls ... there must be some reason for this ... and, if there is ... then, it does not seem reasonable to assume that all controls are equal ... thus, 1 or more controls might be closer to the E than others ... so, why not consider them all and see where the differences might be
do you have any predictions as to the differences? directions? relative size?
---------------------------------------------------------- Dennis Roberts Email: [EMAIL PROTECTED] Web: http://roberts.ed.psu.edu/users/droberts/drober~1.htm
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