>>> "John Fox" <j...@mcmaster.ca> 02/03/2010 02:19 >>> >There's also a serious question about whether one would >be interested in main effects defined as averages over the level of the >other factor when interactions are present.
My personal take on this particular chestnut is that I often want to ask something about the relative size of the effects. If the so-called "main effect(s)" is/are very much larger than the interactions, one may be able to make generalisations which have practical use. If the effects are much of a size, there's nothing much to be gained by asking about "main effects". Mind you, that's probably a crit of significance testing as the be-all and end-all, rather than a problem with type I-III. Asking 'how big is it?' is a step beyond 'is it there?'. Steve E ******************************************************************* This email and any attachments are confidential. Any use...{{dropped:8}} ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.