Ggplot2 Add A Reference Gray Bar To Plot

Ggplot2 Inr Ggplot2 In R Ggplot2 Ggplot 2 R Ggplot2 Ggplot2 Plot R Ggplot 2 Ggplot In R R Ggplot2 Example R Studio Ggplot2 Ggplot2 Code Ggplot R Studio Ggplot2 Barplot Ggplot In R Studio What Is Ggplot2 Ggplot2 Examples Point Type Ggplot2 Ggplot2 Graphics Ggplot2 Bar Graphics In R With Ggplot2 Stats And R