A helper function for sem.missing.paths and sem.partial.resid that retrives (and modifies) the proper random structure for a mixed model to be passed to update.
get.random.formula(model, rhs, modelList, dropterms)a linear model.
the fixed effects formula.
a list of regressions representing the structural equation model.
terms to be dropped from the random structure (optional).
Returns a character vector corresponding to the updated random structure.