|C1||Tree diameter at a certain distance from the ground (in cm)|
|C2||Tree height (in m)|
|C3||Volume of useable timber (in dm3)|
The bivariate plots (Graph > Matrix Plot > Each Y versus each X: Simple) clearly show that the best model with only one regressor is the one that explains the volume as a function of the diameter. In the following, this model is studied in detail:
Stat > Regression > Regression
The plots for the residual analysis (in the dialog box Regression, press button Graphs and choose Four in one) look as follows:
The most notable issue is that in the second graph, residuals versus fitted values (Versus ...