Summarized Data Distributions - R Graphics - page 174

Figure 6-18. Box plot of a single group

NOTE
The calculation of quantiles works slightly differently from the boxplot() function in base R. This can
sometimes be noticeable for small sample sizes. See ?geom_boxplot for detailed information about
how the calculations differ.

Adding Notches to a Box Plot

Problem
You want to add notches to a box plot to assess whether the medians are different.

Solution
Use geom_boxplot() and set notch=TRUE ( Figure 6-19 ):

library(MASS) # For the data set

ggplot(birthwt, aes(x = factor(race), y = bwt)) + geom_boxplot(notch = TRUE TRUE )