I am trying to estimate variance components from a complex random effects survival model using coxme (Package version 2.2-5). I am having problems specifying interaction effects in the random terms. I wonder if this is simply not implemented in coxme yet.
For instance, using the model coxme(Surv(DeathAge,Dead) ~ treatment + (1 | block/tank)) Works fine (tank nested within block), but coxme(Surv(DeathAge,Dead) ~ treatment + (1 | block) + (1 | block:tank)) fails with "Error in getgroups(f2$group, m) : Invalid grouping factor block:tank”. By my understanding of model specification in R, these should be equivalent statements (assuming that that the tank effects have been coded appropriately as unique within blocks). Any interaction specified using “:” appears to fail. I am actually interested in much more complex models but can’t seem to be able to specify any interactions effects. For instance a factorial model like, coxme(Surv(DeathAge,Dead) ~ treatment + (1 | room*block)) fails with "Error in getgroups(f2$group, m) : Invalid grouping factor room * block”. Since I can’t directly specify the interaction effects and the factorial operator “*” does not seem to work, I appear to be SOL. It seems that only nested effects specified by the “/“ operator are allowed. Multiple nesting is also OK, which is great for a single hierarchical nesting design, but not sufficient for more complex random effects models. Any thoughts would be most welcome. Thanks, Patrick ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
