combine_terms {gtsummary}

Combine terms

Description

The function combines terms from a regression model, and replaces the terms with a single row in the output table. The p-value is calculated using stats::anova().

Usage

combine_terms(x, formula_update, label = NULL, quiet, ...)

Arguments

x

(tbl_regression)
A tbl_regression object

formula_update

(formula)
formula update passed to the stats::update(). This updated formula is used to construct a reduced model, and is subsequently passed to stats::anova() to calculate the p-value for the group of removed terms. See the stats::update() function's ⁠formula.=⁠ argument for proper syntax.

label

(string)
Optional string argument labeling the combined rows

quiet

...

Additional arguments passed to stats::anova

Value

tbl_regression object

Author(s)

Daniel D. Sjoberg

Examples

# Example 1 ----------------------------------
# Logistic Regression Example, LRT p-value
glm(response ~ marker + I(marker^2) + grade,
    trial[c("response", "marker", "grade")] |> na.omit(), # keep complete cases only!
    family = binomial) |>
  tbl_regression(label = grade ~ "Grade", exponentiate = TRUE) |>
  # collapse non-linear terms to a single row in output using anova
  combine_terms(
    formula_update = . ~ . - marker - I(marker^2),
    label = "Marker (non-linear terms)",
    test = "LRT"
  )