Four geoms in ggplot2 to visualize uncertainty

In this post, we will learn about four geoms in ggplot2 that are useful for revealing uncertainty in numerical variables with multiple categories. The four geoms, geom_errorbar(), geom_linerange(), geom_crossbar(), and geom_pointrange() are useful when we have categeorical x values and we are interested in the “distribution of y conditional on x and use the aesthetics ymin and ymax to determine the range of the y values”. The third edition of ggplot2 book has a great chapter describing these geoms.

Let us get started by loading tidyverse and palmer penguin pacakges.

library(tidyverse)
library(palmerpenguins)
theme_set(theme_bw(16))

df <- penguins %>%
  drop_na() %>%
  group_by(species) %>%
  summarize(n= n(),
            mean_body_mass= mean(body_mass_g),
            sd = sd(body_mass_g))

df

# A tibble: 3 × 4
  species       n mean_body_mass    sd
  <fct>     <int>          <dbl> <dbl>
1 Adelie      146          3706.  459.
2 Chinstrap    68          3733.  384.
3 Gentoo      119          5092.  501.

Visualizing Uncertainty with geom_crossbar()

df %>%
  ggplot(aes(species, mean_body_mass,
                  ymin = mean_body_mass - sd,
                  ymax = mean_body_mass + sd)) +
  geom_crossbar()
ggsave("visualizing_uncertainty_with_geom_crossbar.png")

Visualizing Uncertainty with geom_errorbar()

df %>%
  ggplot(aes(species, mean_body_mass,
                  ymin = mean_body_mass - sd,
                  ymax = mean_body_mass + sd)) +
  geom_errorbar(linewidth = 1)
ggsave("visualizing_uncertainty_with_geom_errorbar.png")

Visualizing Uncertainty with geom_pointrange()

df %>%
  ggplot(aes(species, mean_body_mass,
                  ymin = mean_body_mass - sd,
                  ymax = mean_body_mass + sd)) +
  geom_pointrange()
ggsave("visualizing_uncertainty_with_geom_pointrange.png")

Visualizing Uncertainty with geom_linerange()

df %>%
  ggplot(aes(species, mean_body_mass,
                  ymin = mean_body_mass - sd,
                  ymax = mean_body_mass + sd)) +
  geom_linerange(color="blue", linewidth=2)
ggsave("visualizing_uncertainty_with_geom_linerange.png")