Reading for multiple linear regression

Optional:

• Data Analysis Using Regression and Multilevel/Hierarchical Models by Gelman A., and Hill, J.:
  • Section 3: Linear regression: the basics
  • Section 4: Linear regression: before and after fitting the model
• An Introduction to Statistical Learning with Applications in R by James, G., Witten, D., Hastie, T., and Tibshirani, R.:
  • Section 3: Linear regression (you can skip section 3.5)