Hi, I would like to do a meta-analysis, i.e., a mixed-effects regression, but I don't seem to get what I want using both the nlme or metafor packages.
My question: is there indeed no way to do it? And if so, is there another package I could use? Here are the details: In my meta-analysis I'm comparing different studies that report a measure at time zero and after a certain followup time. Each reported measurement comes with standard error, and each study uses one (or several) of a few treatment categories. I want to fit a random effect for each study (the study effect) and a treatment-dependent time effect. For the moment I use a linear model, i.e., twice the followup time will give you twice the effect, etc... I get /almost/ what I want using "nlme" via this command: lme01 <- lme(effect ~ treatment + treatment*time - time - 1, random = ~ 1|study, weights = varFixed(~se2), data = dat) "effect" is the real-valued measurement, "treatment" is a factor, and "time" is the followup time in months. "se2" is the squared standard error. Problem is: using the "varFixed()" option, "lme()" will fit an additional variance parameter scaling the provided standard errors by a certain factor to be estimated. According to some discussions on the web, you once were able to prevent the fitting of the extra variance parameter in some pre-1998 S-plus versions of nlme using a "lmeControl(sigma=1)" option, but this does not appear to available any more. I again get /almost/ what I want using the "metafor" package: rma01 <- rma(yi = effect, vi = se2, mods = ~ treatment + treatment*time - time - 1, data = dat) "rma()" will correctly digest the provided standard errors, but this time the problem is that "rma()" will always treat each line in the data set as a different study, there does not appear to be a way to tell "rma()" that several data points belong to the same study, i.e., have a common random effect. What I am missing is an equivalent to the "random" statement in the "lme()" command above. Adding an option like "slab=as.character(dat$study)" only seems to affect the labeling but not the actual computation. Any ideas? Many thanks in advance, Christian Roever ______________________________________________ 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.