Obtain empirical start value for unstructured covariance
emp_start(
y_vector,
x_matrix,
full_frame,
visit_var,
subject_var,
subject_groups,
...
)A numeric vector of starting values.
(numeric) response variable.
(matrix) design matrix.
(data.frame) full data frame used for model fitting.
(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.