Add or remove a covariate term from an exposure-response TTE model

Add or remove a single covariate term from an existing ertte model, returning a new fitted model object.

Usage

ertte_add_term(mod, term, quiet = FALSE)

ertte_remove_term(mod, term, quiet = FALSE)

Arguments

mod: An ertte model object, as returned by ertte_aft() or ertte_coxph()
term: A one-sided formula naming the term to add/remove, e.g. ~ sex
quiet: If TRUE, suppress the warning issued when the term can't be added/removed (because it's already in the model / isn't in the model, respectively). Defaults to FALSE.

Value

An ertte model object. If the term can't be added/removed (see quiet), the original mod is returned unchanged.

Details

These functions are not typically called directly; they underpin ertte_scm_forward() and ertte_scm_backward(). Named and shaped to match the companion erglm package's erglm_add_term()/erglm_remove_term(): term/candidates are plain formula terms, added/removed additively – categorical covariates enter as factor levels, continuous covariates enter linearly by default or, for a power-function parameterisation (theta such that T ~ (x / ref)^theta on the AFT time scale, or h(t|x) ~ h0(t) * (x / ref)^theta on the Cox hazard scale), by wrapping the covariate in ertte_power(), e.g. ~ ertte_power(age) or candidates = "ertte_power(age)". Term handling here works generically on formula term-labels, so ertte_power() terms need no special-casing.

mod is refit using the matching engine constructor (ertte_aft()/ertte_coxph()), based on its class – so these functions (and the SCM family built on them) work for both ertte_aft and ertte_coxph models.

Examples

mod <- ertte_aft(Surv(time, event) ~ aucss, ertte_data)
mod2 <- ertte_add_term(mod, ~ sex)
mod3 <- ertte_remove_term(mod2, ~ sex)