Hi Paul, Changing the factor levels will work (as you saw). In this case, you could also edit the contrast matrix.
## look at default contrasts contrasts(gad$dosegrp) model1 <- lm(hama ~ dosegrp, data = gad) summary(model1) ## choose group 3 as base (comparison) contrasts(gad$dosegrp) <- contr.treatment(n = 3, base = 3) model1 <- lm(hama ~ dosegrp, data = gad) summary(model1) If you have MASS 4th ed., I believe a discussion of contrast matrices starts on page 146. As far as improvements, in general, I think it would be preferable to let R's method dispatch system choose the method for summary rather than specifying summary.aov() yourself. You might also consider more spaces (e.g., between arguments). Cheers, Josh On Tue, Mar 1, 2011 at 3:45 PM, Paul Miller <pjmiller...@yahoo.com> wrote: > Hello Everyone, > > Figured out one part of the code. Setting the reference level for a factor is > accomplished using the relevel funtion (pg. 383 of MASS; pg. 70 of Data > Manipulation with R): > > gad$dosegrp <- relevel(gad$dosegrp,3) > > This works very well. Much better than using a format in SAS procedures that > don't allow the "ref=" option for instance. > > Does anyone have suggestions about how to improve other aspects of my code? > > Thanks, > > Paul > ______________________________________________ > 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. -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles http://www.joshuawiley.com/ ______________________________________________ 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.
