Define a Covariance Structure

Usage

cov_struct(
  type = cov_types(),
  visits,
  subject,
  group = character(),
  heterogeneous = FALSE
)

Arguments

type

(string)
the name of the covariance structure type to use. For available options, see cov_types(). If a type abbreviation is used that implies heterogeneity (e.g. cph) and no value is provided to heterogeneous, then the heterogeneity is derived from the type name.

visits

(character)
a vector of variable names to use for the longitudinal terms of the covariance structure. Multiple terms are only permitted for the "spatial" covariance type.

subject

(string)
the name of the variable that encodes a subject identifier.

group

(string)
optionally, the name of the variable that encodes a grouping variable for subjects.

heterogeneous

(flag)

Value

A cov_struct object.

See also

Other covariance types: as.cov_struct(), covariance_types

Examples

cov_struct("csh", "AVISITN", "USUBJID")
#> <covariance structure>
#> heterogeneous compound symmetry:
#> 
#>   AVISITN | USUBJID
#>  
cov_struct("spatial", c("VISITA", "VISITB"), group = "GRP", subject = "SBJ")
#> <covariance structure>
#> spatial exponential:
#> 
#>   VISITA, VISITB | GRP / SBJ
#>