Prof Brian Ripley wrote:
On Fri, 5 Mar 2004, pallier wrote:Thanks.
...
Actually, the different types of main effects defined above just correspond to different
contrasts on the cell means. So if there is an easy solution to compute arbitrary contrasts
on the cell means in a factorial design, this could an approach to this
question. (Anyone?)
There are at least three such ways. ?contrasts (for the assignment
function contrasts<-) and ?C, as well as the contrasts= argument to aov (the function you were discussing ...).
I know the existence of 'contrasts' and I read the section about contrasts matrix in your book (MASS 3rd edition), as well as
in the R online documentation, but I probably do not understand them well: It still escapes me how to proceed to compute
"arbitrary" contrasts, such as, say:
a1b1 a1b2 a2b1 a2b2 1 1 -1 -1
a1b1 a1b2 a2b1 a2b2 .5 .5 -1 0
in a model "x~ a * b" where a and b are two binary factors.
(the contrasts should be on the cell means, ignoring the sample size of subgroups. I know how to compute the size of the contrasts from the table of means returned by tapply, but I whould also need the associated MSE).
Sorry if the solution is obvious.
Christophe Pallier
______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
