In ggplot2, the geom_smooth () function is used to add a smooth line or curve to a plot. It is commonly used to visualize the trend or relationship between variables.

The function will look to the dataset defined in the first `ggplot ()` function, in this case `nmes.data`, to find the variables it needs for x and y, in this case `age` and `bmi`. ``` {r} ggplot ...