Sometimes, you may want to include interaction or polynomial terms in your multiple linear regression model, to capture the effect of two or more independent variables together, or the effect of a ...

With only one variable in the model, it is unclear whether Visa affects the S&P 500 prices, if the S&P 500 affects V prices, or if some unobserved third variable affects both prices.

Simple linear regression relates two variables (X and Y) with a straight line (y = mx + b), ... so you can choose the correct regression model, whether linear or nonlinear.

Multiple linear regression uses two or more independent variables to predict a dependent variable. The result is an equation you can use to estimate future outcomes based on known data.