Empirical Starting Value

Obtain empirical start value for unstructured covariance

emp_start(data, model_formula, visit_var, subject_var, subject_groups, ...)

Arguments

data

(data.frame)
data used for model fitting.

model_formula

(formula)
the formula in mmrm model without covariance structure part.

visit_var

(string)
visit variable.

subject_var

(string)
subject id variable.

subject_groups

(factor)
subject group assignment.

...

not used.

Value

A numeric vector of starting values.

Details

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.

Note

data is used instead of full_frame because full_frame is already transformed if model contains transformations, e.g. log(FEV1) ~ exp(FEV1_BL) will drop FEV1 and FEV1_BL but add log(FEV1) and exp(FEV1_BL) in full_frame.