Obtain empirical start value for unstructured covariance
emp_start(data, model_formula, visit_var, subject_var, subject_groups, ...)A numeric vector of starting values.
(data.frame)
data used for model fitting.
(formula)
the formula in mmrm model without covariance structure part.
(string)
visit variable.
(string)
subject id variable.
(factor)
subject group assignment.
not used.
This emp_start only works for unstructured covariance structure.
It uses linear regression to first obtain the coefficients and use the residuals
to obtain the empirical variance-covariance, and it is then used to obtain the
starting values.