ggsignif: R Package for Displaying Significance Brackets for 'ggplot2'

Research hypotheses are often concerned with the difference between two groups and statistical tests provide indicators (like p-values or Bayes factors) about the evidence for or against such differences. The R package, ggsignif provides a quick way to visualize such pairwise indicators as an annotation in a plot, for example showing if a difference is statistically significant. ggsignif follows the principles of the grammar of graphics (Wilkinson, 2012) and provides a new layer that can be added to plots made with the ggplot2 package (Wickham, 2016).