random_effects_expr function

Construct random effects formula

Constructs a character representation of the random effects formula for fitting a MMRM for subject by visit in the format required for mmrm::mmrm().

random_effects_expr(
  cov_struct = c("us", "ad", "adh", "ar1", "ar1h", "cs", "csh", "toep", "toeph"),
  cov_by_group = FALSE
)

Arguments

• cov_struct: Character - The covariance structure to be used, must be one of "us" (default), "ad", "adh", "ar1", "ar1h", "cs", "csh", "toep", or "toeph")
• cov_by_group: Boolean - Whenever or not to use separate covariances per each group level

Details

For example assuming the user specified a covariance structure of "us" and that no groups were provided this will return

us(visit | subjid)

If cov_by_group is set to FALSE then this indicates that separate covariance matrices are required per group and as such the following will be returned:

us( visit | group / subjid )