Is there a way to specify a Z matrix using the lmer function, where the model is written as y = X*Beta + Z*u + e?
I am trying to reproduce smoothing methods illustrated in the paper "Smoothing with Mixed Model Software" my Long Ngo and M.P. Wand. published in the /Journal of Statistical Software/ in 2004 using the lme4 and Matrix packages. The code and data sets used can be found at http://www.jstatsoft.org/v09/i01/. There original code did not work for me without slight modifications here is the code that I used with my modifications noted. x <- fossil$age y <- 100000*fossil$strontium.ratio knots <- seq(94,121,length=25) n <- length(x) X <- cbind(rep(1,n),x) Z <- outer(x,knots,"-") Z <- Z*(Z>0) # I had to create the groupedData object with one group to fit the model I wanted grp <- rep(1,n) grp.dat<-groupedData(y~Z|grp) fit <- lme(y~-1+X,random=pdIdent(~-1+Z),data=grp.dat) I would like to know how I could fit this same model using the lmer function. Specifically can I specify a Z matrix in the same way as I do above in lme? Thanks, Mark ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
