Add differences between groups

Adds difference to tables created by tbl_summary(). The difference between two groups (typically mean or rate difference) is added to the table along with the difference's confidence interval and a p-value (when applicable).

Usage

# S3 method for class 'tbl_svysummary'
add_difference(
  x,
  test = NULL,
  group = NULL,
  adj.vars = NULL,
  test.args = NULL,
  conf.level = 0.95,
  include = everything(),
  pvalue_fun = label_style_pvalue(digits = 1),
  estimate_fun = list(c(all_continuous(), all_categorical(FALSE)) ~ label_style_sigfig(),
    all_dichotomous() ~ label_style_sigfig(scale = 100, suffix = "%"), all_tests("smd")
    ~ label_style_sigfig()),
  ...
)

Arguments

x

(tbl_summary)
table created with tbl_summary()

test

(formula-list-selector)
Specifies the tests/methods to perform for each variable, e.g. list(all_continuous() ~ "svy.t.test", all_dichotomous() ~ "emmeans", all_categorical(FALSE) ~ "svy.chisq.test").

See below for details on default tests and ?tests for details on available tests and creating custom tests.

group

(tidy-select)
Variable name of an ID or grouping variable. The column can be used to calculate p-values with correlated data. Default is NULL. See tests for methods that utilize the group argument.

adj.vars

(tidy-select)
Variables to include in adjusted calculations (e.g. in ANCOVA models). Default is NULL.

test.args

(formula-list-selector)
Containing additional arguments to pass to tests that accept arguments. For example, add an argument for all t-tests, use test.args = all_tests("t.test") ~ list(var.equal = TRUE).

conf.level

(numeric)
a scalar in the interval (0, 1) indicating the confidence level. Default is 0.95

include

(tidy-select)
Variables to include in output. Default is everything().

pvalue_fun

(function)
Function to round and format p-values. Default is label_style_pvalue(). The function must have a numeric vector input, and return a string that is the rounded/formatted p-value (e.g. pvalue_fun = label_style_pvalue(digits = 2)).

estimate_fun

(formula-list-selector)
List of formulas specifying the functions to round and format differences and confidence limits. Default is list(c(all_continuous(), all_categorical(FALSE)) ~ label_style_sigfig(), all_categorical() ~ \(x) paste0(style_sigfig(x, scale = 100), "%"))

...

These dots are for future extensions and must be empty.

Value

a gtsummary table of class "tbl_summary"

Examples

# Example 1 ----------------------------------
survey::svydesign(~1, data = as.data.frame(Titanic), weights = ~Freq) |>
  tbl_svysummary(
    by = Survived,
    value = list(Class ~ "1st", Age = "Child"),
    include = c(Class, Age)
  ) |>
  add_difference()
#> The following warnings were returned during `add_difference()`:
#> ! For variable `Age` (`Survived`) and "estimate", "std.error", "conf.low",
#>   "conf.high", and "p.value" statistics: non-integer #successes in a binomial
#>   glm!
#> ! For variable `Class` (`Survived`) and "estimate", "std.error", "conf.low",
#>   "conf.high", and "p.value" statistics: non-integer #successes in a binomial
#>   glm!


  
Characteristic
      
No

N = 1,4901
      
Yes

N = 7111
      
Difference2
      
95% CI2
      
p-value2
    
Class
122 (8.2%)
203 (29%)
20%
-19%, 60%
0.3
Age
52 (3.5%)
57 (8.0%)
4.5%
-6.6%, 16%
0.4
1 n (%)
    
2 Least-squares mean difference
    
Abbreviation: CI = Confidence Interval