Violin plot with confidence interval in r

Question

How can I add a confidence interval to this violin plot?

df <- data.frame("Need" = c(3,4.3,4.5,2.2,5.1,5.2), "Condition" = c("A","A","A","B","B","B"))

ggplot(df,aes(x = Condition, y = Need, fill=Condition)) +
           geom_violin() +
           stat_summary(fun.data = "mean_cl_boot", geom = "pointrange",
                         colour = "red") +
           ggtitle("Needs by condition violin plot"))

I can't attach pictures yet, but you get the gist. With this code I can create violin plots with standard deviation lines for each violin plot, but I'd add 95% confidence interval lines.

Any ideas?

Answer 1

What you can do is first calculate the error bars per condition and after that add them by using geom_errorbar like this:

library(tidyverse)
stats <- df %>% 
  group_by(Condition) %>%
  summarise(Mean = mean(Need), SD = sd(Need),
            CI_L = Mean - (SD * 1.96)/sqrt(6),
            CI_U = Mean + (SD * 1.96)/sqrt(6))

ggplot() +
  geom_violin(df, mapping = aes(x = Condition, y = Need, fill=Condition)) +
  stat_summary(fun.data = "mean_cl_boot", geom = "pointrange",
               colour = "red") +
  geom_point(stats, mapping = aes(Condition, Mean)) +
  geom_errorbar(stats, mapping = aes(x = Condition, ymin = CI_L, ymax = CI_U), width = 0.2) +
  ggtitle("Needs by condition violin plot")

Output: