Adding Comparison Annotations to Boxplots

Boxplot with Tukey Comparison Bars

I had run an ANOVA test and found that at least one of the means among my groups were statistically significantly different. As follow-up analysis, I ran a Tukey test and found which groups differed in means, and I'm hoping to illustrate this in a boxplot as presented in this paper, Effects of intermittent Pringle's manoeuvre on cirrhotic compared with normal liver: https://academic.oup.com/bjs/article/97/7/1062/6150536?login=true

I can generate the boxplot, but I want to add bar(s) that illustrates which groups significantly differ in mean with the asterik, as highlighted in the image. Anyone know how I could approach this, ideally in SAS or R?

In SAS, I've used PROC SGPLOT to generate the boxplot, and in R, I know I can use geom_boxplot, but as for any additional annotations, I'm not sure what options are available to accomplish this.

In Base R you can generate these lines manually if you want more granular control, or for a quick and seemingly automated approach use ggstatsplot::ggbetweenstats (among other approaches, I'm sure):

Data

df <- data.frame(DAST = 1:300,
                 Category = rep(c("Normal", "Chronic Hepatitis", "Liver Cirrhosis"), each = 100))

ggbetweenstats approach

see ?ggstatsplot::ggbetweenstats for a wide range of options on how to customize

library(ggplot2)
library(ggstatsplot)

ggstatsplot::ggbetweenstats(df, x = Category, y = DAST)

Base R approach

Colored lines for clarity

# vertical spacing between bars
v_spacing <- c(max(df$DAST) + seq(20, 50, length.out = 3))

plot(x = as.factor(df$Category), y = df$DAST,
     xlab = NA, ylab = "D-AST", frame = FALSE)
# horizontal lines - position 1 = Chronic Hepatitis, 2 = Liver Cirrhosis, 3 = Normal
  # bars map between positions 1-2, 1-3, 2-3
segments(x0 = c(1,1,2), 
         x1 = c(2,3,3),
         y0 = v_spacing,
         xpd = TRUE,
         col = c("red", "green", "blue"))

# vertical lines
segments(x0 = c(1, 2, 1, 3, 2, 3), 
         y0 = rep(v_spacing, each = 2),
         y1 = rep(v_spacing, each = 2) - 5,
         xpd = TRUE,
         col = rep(c("red", "green", "blue"), each = 2))

# Denote significance
text("*", 
     x = c(mean(1:2), mean(c(1,3)), mean(2:3)),
     y = v_spacing + 5,
     xpd = TRUE,
     col = c("red", "green", "blue"))