Dear David and Andy, First, my apologies for somehow missing the original message.
Andy has it right: xlevels refers to the predictors in the term corresponding to the effect to be computed. His solution is clever -- I wouldn't have thought of it -- but it could get you into trouble in a more complicated model. Another possibility is to specify an effect that includes both predictors (i.e., the Sex*Age effect, which is higher-order to the terms actually in the model), and to set Age to the desired value in xlevels. At present, effect() wants more than one value for each variable in the xlevels list. I'll look at changing that, but at present you could do something like effect("Sex*Age", mod, xlevels=(Age=c(120,120))) This should get you what you want, albeit redundantly. I hope that this helps, John On Wed, 9 Jun 2004 09:40:49 -0400 "Liaw, Andy" <[EMAIL PROTECTED]> wrote: > Prof. Fox will be able to give the definitive answer, but from my > reading of > ?effect, xlevels refers to the values of the factor whose effect > you're > interested in, not the ones being `marginalized'. I believe you need > to > play with the `typical' argument. > > HTH, > Andy > > > From: David J. Netherway > > > > library(effects) > > mod <- lm(Measurement ~ Age + Sex, data=d) > > e <-effect("Sex",mod) > > > > The effect is evaluated at the mean age. > > > > > e > > Sex effect > > Sex > > F M > > 43.33083 44.48531 > > > > > > e$model.matrix > > (Intercept) Age SexM > > 1 1 130.5859 0 > > 23 1 130.5859 1 > > > > To evaluate the effect at Age=120 I tried: > > e <-effect("Sex",mod,xlevels=list(Age=c(120))) > > but the effect was still evaluated at 130.5859. > > > > Is this an incorrect usage of xlevels? > > > > Thanks, David > > > > ______________________________________________ > > [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 > > > > > > ______________________________________________ > [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 -------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada http://socserv.mcmaster.ca/jfox/ ______________________________________________ [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