Create Compact Letter Display Layer Groups with at least one letter in common are not significantly different.

Usage

geom_tukey(
  test = c("tukey", "kruskalmc", "dunn"),
  type = c("two-way", "one-way"),
  threshold = 0.05,
  where = c("box", "whisker", "mean", "median", "se", "sd", "cl_normal", "cl_boot"),
  hjust = 0,
  vjust = -0.2,
  geom = "text",
  size = 4,
  color = "black",
  fill = "white",
  alpha = 1,
  na.rm = TRUE,
  reversed = FALSE
)

Arguments

test: Which test to run for pairwise comparisons. Either tukey (the default), kruskalmc, or dunn_test.
type: If a grouping variable is provided, determines whether to run separate tests for each facet (one-way) or one (two-way) test with an interaction term between x and group. Defaults to two-way.
threshold: Statistical threshold for significance. Defaults to 0.05.
where: Where to put the letters. Either above the box (box) or upper whisker (whisker) of a boxplot; at the mean or median; or at the top of the error bars calculated from the standard error (se), standard deviation sd, or 95% confidence intervals returned by smean.cl.normal, or smean.cl.boot.
hjust: Horizontal adjustment of the label. (Argument to geom_text).
vjust: Vertical adjustment of the label. (Argument to geom_text).
geom: Which geom to use to plot letters. Options are text and label.
size: Label size. Argument to geom_text.
color: Label color.
fill: Label fill (only applies if geom == "label").
alpha: Label transparency. Defaults to 1.
na.rm: Logical. Whether to remove observations with NAs for the provided factors (i.e. x and group) before plotting. Defaults to TRUE.
reversed: Logical. Argument to multcompLetters3. Determines whether order of letters should be reversed. Defaults to FALSE.

Note

Thank you to Hiroaki Yutani and Simon P. Couch for a couple of very helpful blog posts (1, 2) describing the ggplot_add syntax.

References

Piepho, Hans-Peter. An Algorithm for a Letter-Based Representation of All-Pairwise Comparisons. Journal of Computational and Graphical Statistics 13, no. 2 (June 1, 2004): 456–66. doi:10.1198/1061860043515 .
Piepho, Hans-Peter. “Letters in Mean Comparisons: What They Do and Don’t Mean.” Agronomy Journal 110, no. 2 (2018): 431–34. doi:10.2134/agronj2017.10.0580
Graves S, Piepho H, Dorai-Raj LSwhfS (2019). multcompView: Visualizations of Paired Comparisons. R package version 0.1-8. https://CRAN.R-project.org/package=multcompView

Author

Ethan Bass

Examples

library(ggplot2)
set.seed(1)
data <- data.frame("Category" = c(rep("Low", 10), rep("Medium", 10), rep("High", 10)),
                  "Value" = c(rnorm(10, 5), rnorm(10, 5.5), rnorm(10, 10)),
                  "Size" = c("Big","Small"))
data |> ggplot(aes(x=Category, y=Value)) + geom_boxplot() + facet_wrap(~Size) + geom_tukey()

data |> ggplot(aes(x=Size, y=Value)) + geom_boxplot() + facet_wrap(~Category) + geom_tukey()