Analysis of Residuals

The analysis of residuals is important for any regression model. While numerical analysis is more profound, practice shows that numerical tests are unsatisfactory for small samples. However, it is possible to use graphical methods for analyzing residuals. This usually gives better results, since the human brain is trained to recognize patterns. Thus plots of the residuals against the independent variable usually give hints as to  whether the assumptions of a least squares regression are fulfilled. The following slide show displays some examples of data sets which do not fulfill these assumptions.