Set up an unstructured (UNSTR) correlation term in brms. The function does
not evaluate its arguments – it exists purely to help set up a model with
UNSTR terms.
Arguments
- time
An optional time variable specifying the time ordering
of the observations. By default, the existing order of the observations
in the data is used.
- gr
An optional grouping variable. If specified, the correlation
structure is assumed to apply only to observations within the same grouping
level.
Value
An object of class 'unstr_term', which is a list
of arguments to be interpreted by the formula
parsing functions of brms.
Examples
if (FALSE) { # \dontrun{
# add an unstructured correlation matrix for visits within the same patient
fit <- brm(count ~ Trt + unstr(visit, patient), data = epilepsy)
summary(fit)
} # }