Compare one level of a factor with *all* other non-missing levels
On 2010-12-10 05:58, deriK2000 wrote:
Peter Ehlers wrote:
Sounds like you want the Dunnett test procedure which seems to be implemented in a number of packages: multcomp, asd, MCPAN and others. It would probably be a good idea to install package 'sos' and learn how to search with it. Peter Ehlers
Thanks for the hints! Unfortunately, Dunnett compares the mean(x) for a factor level with the means(x) of all single K-1 other levels resulting in K-1 comparisions for each level (printed in a lower triangular matrix for the results). Instead, I just want to compare this one mean(x) with one other mean(x) of all the K-1 other levels (printed in a vector of length K for the results).
Okay, I misunderstood; should have read more carefully.
I would just use a loop (I'm not as loop-averse as
some R users).
x <- rnorm(20)
f <- gl(4, 5, lab = letters[1:4])
lev <- levels(f)
len <- length(lev)
pv <- numeric(len)
for(i in 1:len){
pv[i] <- t.test(x[f == lev[i]], x[f != lev[i]])$p.value
}
pv
For pvalue adjustment (if you think that's needed),
see ?p.adjust.
Concerning sos: sounds like a good idea!
Yes, it's an excellent tool. Peter Ehlers
Cheers, Derik