The simple linear regression model considers the relationship between two variables and in many cases more information will be available that can be used to extend the model. For example, there might be a categorical variable (sometimes known as a covariate) that can be used to divide the data set to fit a separate linear
M. Gschwandtner, und P. Filzmoser. Synergies of Soft Computing and Statistics for Intelligent Data Analysis, Volume 190 von Advances in Intelligent Systems and Computing, Springer Berlin Heidelberg, (2013)