ggsignif: Significance Brackets for ‘ggplot2’

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This package provides an easy way to indicate if two groups are significantly different. Commonly this is shown by a bar on top connecting the groups of interest which itself is annotated with the level of significance (NS, *, **, ***). The package provides a single layer (geom_signif) that takes the groups for comparison and the test (t.test, wilcox etc.) and adds the annotation to the plot.


Install package


# Or for the latest development version

Plot significance


ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
    comparisons = list(c("compact", "midsize"), c("minivan", "suv")),
    map_signif_level = TRUE, textsize = 6
  ) +
  ylim(NA, 48)

Setting the precise location

This is important if you use position="dodge", because in that case I cannot calculate the correct position of the bars automatically.

# Calculate annotation
anno <- t.test(
  iris[iris$Petal.Width > 1 & iris$Species == "versicolor", "Sepal.Width"],
  iris[iris$Species == "virginica", "Sepal.Width"]

# Make plot with custom x and y position of the bracket
ggplot(iris, aes(x = Species, y = Sepal.Width, fill = Petal.Width > 1)) +
  geom_boxplot(position = "dodge") +
    annotation = formatC(anno, digits = 1),
    y_position = 4.05, xmin = 2.2, xmax = 3,
    tip_length = c(0.2, 0.04)

Advanced Example

Sometimes one needs to have a very fine tuned ability to set the location of the the significance bars in combination with facet_wrap or facet_grid. In those cases it you can set the flag manual=TRUE and provide the annotations as a data.frame:

annotation_df <- data.frame(
  color = c("E", "H"),
  start = c("Good", "Fair"),
  end = c("Very Good", "Good"),
  y = c(3.6, 4.7),
  label = c("Comp. 1", "Comp. 2")

#>   color start       end   y   label
#> 1     E  Good Very Good 3.6 Comp. 1
#> 2     H  Fair      Good 4.7 Comp. 2

ggplot(diamonds, aes(x = cut, y = carat)) +
  geom_boxplot() +
    data = annotation_df,
    aes(xmin = start, xmax = end, annotations = label, y_position = y),
    textsize = 3, vjust = -0.2,
    manual = TRUE
  ) +
  facet_wrap(~color) +
  ylim(NA, 5.3)

You can ignore the warning about the missing aesthetics.

For further details go the CRAN page and check the examples in the vignette.


This package is provided as is and I currently don’t have any plans and the capacity to add any new features to it. If there is nonetheless a feature which you would like to see in the package, you are always welcome to submit pull request, which I will try to address as soon as possible.

Code of Conduct

Please note that the ggsignif project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.