Create design matrix of sample selection model
# S3 method for heckitrob
model.matrix(object, part = "outcome", ...)object of class heckitrob
character string indicating which matrix to extract: "outcome" for the outcome equation, "selection" for the selection equation.
currently not used
If argument part is "outcome", the design matrix of the outcome equation is returned.
If argument part is "selection", the design matrix of the selection equation is returned.