Check that all variables in formulas are in the data
check_vars_in_data(datanames, fixed = NULL, random = NULL,
auxvars = NULL, timevar = NULL)nothing, but throws an error if a variable is missing
a character vector (of all variable names in the data)
the fixed effects formula (or list of formulas)
the random effects formula (or list of formulas)
one-sided formula of auxiliary variables
a character string (name of the time variable, used in joint models)