RGraphGallery

• load data (part of the lme4 package)

data(sleepstudy)
head(sleepstudy)

  Reaction Days Subject
1 249.5600    0     308
2 258.7047    1     308
3 250.8006    2     308
4 321.4398    3     308
5 356.8519    4     308
6 414.6901    5     308

• and build the graph using a linear model (method="lm" in the geom)

ggplot(sleepstudy,aes(x=Days,y=Reaction)) +
  geom_point() +
  geom_smooth(method="lm")