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.

term

A one-sided formula naming the term to add/remove, e.g. ~ sex.

quiet

Should the warning issued when the term can't be added/removed (because it's already in the model / isn't in the model, respectively) be suppressed? 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(), used to add or remove a single term from a time-to-event regression model. mod is refit using the matching engine constructor based on its class, so these functions work for both ertte_aft and ertte_coxph models. Regardless of whether the model is a parametric AFT model or a Cox proportional hazard model, the term to be added or removed is defined by a single one-sided formula. Categorical covariates enter the model as factor levels, whereas continuous covariates enter as linear terms by default. However, 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), the covariate can be wrapped in ertte_power(), e.g. ~ ertte_power(age).

Examples

mod1 <- ertte_aft(Surv(time, event) ~ aucss, ertte_data)
mod2 <- ertte_add_term(mod1, ~ sex)
mod3 <- ertte_remove_term(mod2, ~ sex)