I have a data set with 50 different x values and 5 values for the sampling variance; each of the 5 sampling variances corresponds to 10 particular x values. I am trying to fit a mixed effect linear model and I'm not sure about the syntax for specifying the fixed variance structure. In Pinheiro's book my situation appears to be similar to the example used for varIdent, where there is a fixed value for variance for females, and a a different fixed variance for males. The following syntax is used: varIdent(form~1|sex, fixed=c(Female=.5)) or something to that effect. So for the 'fixed' part of the argument, I need to specify that certain x'values have variance a, certain ones have variance b, and so on. I assume that the formula argument in my case is written ~1|x which tells the function that the variance is fixed and depends on the x-values. Any ideas for how to specify different fixed variances for certain x-values?
Thanks Joanne Ellis -- View this message in context: http://r.789695.n4.nabble.com/Fixed-variance-structure-for-lme-tp2955239p2955239.html Sent from the R help mailing list archive at Nabble.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.
