add_stat {gtsummary}

Add a custom statistic

Description

The function allows a user to add a new column (or columns) of statistics to an existing tbl_summary, tbl_svysummary, or tbl_continuous object.

Usage

add_stat(x, fns, location = everything() ~ "label")

Arguments

x

(tbl_summary/tbl_svysummary/tbl_continuous)
A gtsummary table of class 'tbl_summary', 'tbl_svysummary', or 'tbl_continuous'.

fns

(formula-list-selector)
Indicates the functions that create the statistic. See details below.

location

(formula-list-selector)
Indicates the location the new statistics are placed. The values must be one of c("label", "level", "missing"). When "label", a single statistic is placed on the variable label row. When "level" the statistics are placed on the variable level rows. The length of the vector of statistics returned from the fns function must match the dimension of levels. Default is to place the new statistics on the label row.

Value

A 'gtsummary' of the same class as the input

Details

The returns from custom functions passed in ⁠fns=⁠ are required to follow a specified format. Each of these function will execute on a single variable.

1. Each function must return a tibble or a vector. If a vector is returned, it will be converted to a tibble with one column and number of rows equal to the length of the vector.

2. When location='label', the returned statistic from the custom function must be a tibble with one row. When location='level' the tibble must have the same number of rows as there are levels in the variable (excluding the row for unknown values).

3. Each function may take the following arguments: foo(data, variable, by, tbl, ...)

   • ⁠data=⁠ is the input data frame passed to tbl_summary()

   • ⁠variable=⁠ is a string indicating the variable to perform the calculation on. This is the variable in the label column of the table.

   • ⁠by=⁠ is a string indicating the by variable from ⁠tbl_summary=⁠, if present

   • ⁠tbl=⁠ the original tbl_summary()/tbl_svysummary() object is also available to utilize

The user-defined function does not need to utilize each of these inputs. It's encouraged the user-defined function accept ... as each of the arguments will be passed to the function, even if not all inputs are utilized by the user's function, e.g. foo(data, variable, by, ...)

• Use modify_header() to update the column headers

• Use modify_fmt_fun() to update the functions that format the statistics

• Use modify_footnote() to add a explanatory footnote

If you return a tibble with column names p.value or q.value, default p-value formatting will be applied, and you may take advantage of subsequent p-value formatting functions, such as bold_p() or add_q().

Examples

# Example 1 ----------------------------------
# fn returns t-test pvalue
my_ttest <- function(data, variable, by, ...) {
  t.test(data[[variable]] ~ as.factor(data[[by]]))$p.value
}

trial |>
  tbl_summary(
    by = trt,
    include = c(trt, age, marker),
    missing = "no"
  ) |>
  add_stat(fns = everything() ~ my_ttest) |>
  modify_header(add_stat_1 = "**p-value**", all_stat_cols() ~ "**{level}**")

# Example 2 ----------------------------------
# fn returns t-test test statistic and pvalue
my_ttest2 <- function(data, variable, by, ...) {
  t.test(data[[variable]] ~ as.factor(data[[by]])) |>
    broom::tidy() %>%
    dplyr::mutate(
      stat = glue::glue("t={style_sigfig(statistic)}, {style_pvalue(p.value, prepend_p = TRUE)}")
    ) %>%
    dplyr::pull(stat)
}

trial |>
  tbl_summary(
    by = trt,
    include = c(trt, age, marker),
    missing = "no"
  ) |>
  add_stat(fns = everything() ~ my_ttest2) |>
  modify_header(add_stat_1 = "**Treatment Comparison**")

# Example 3 ----------------------------------
# return test statistic and p-value is separate columns
my_ttest3 <- function(data, variable, by, ...) {
  t.test(data[[variable]] ~ as.factor(data[[by]])) %>%
    broom::tidy() %>%
    select(statistic, p.value)
}

trial |>
  tbl_summary(
    by = trt,
    include = c(trt, age, marker),
    missing = "no"
  ) |>
  add_stat(fns = everything() ~ my_ttest3) |>
  modify_header(statistic = "**t-statistic**", p.value = "**p-value**") |>
  modify_fmt_fun(statistic = label_style_sigfig(), p.value = label_style_pvalue(digits = 2))