Two kind of variables are used in models with individual heterogenetiy: the typical
variables that enter in the latent process and those variables that enter in the random
parameter (Hierarchical Model). rFormula
deal with this type of models using
suitable methods to extract the elements of the model.
rFormula(object)is.rFormula(object)
# S3 method for rFormula
model.frame(formula, data, ..., lhs = NULL, rhs = NULL)
# S3 method for rFormula
model.matrix(object, data, rhs = NULL, ...)