Plotting a regression line

All of us have studied regressions or at least heard about them in newspapers or journal articles. Regression lines are a visual representation of the regression equation. Gareth, Witten, Hastie, and Tibshirani in the book An Introduction to Statistical Learning, have defined a simple linear regression as, "it is a very straightforward approach for predicting a quantitative response Y on the basis of a single predictor variable X. It assumes that there is approximately a linear relationship between X and Y". Readers should refer to chapter 3 of that book to learn the concept of linear regression and its application using R.

From the preceding plot, we observe that horsepower has a negative relationship with miles per gallon (mpg).

How to do it…

We will first load our data using the ISLR package. We are loading the package to use the data file and this is not required if you would like to use your own imported data:

install.packages("ISLR")
library(ISLR)

To generate...