There are two kinds of interpretation involved in your question: interpretation of the tests of the parameter estimates and the interpretation of the model predictions.
The three terms in the model are significant. You should not delete any of them or you will bias the model.
The predictions are correct. The traces seen in the Prediction Profiler are based on the model and the given factor levels. The interaction effect (2.5) is almost as large in magnitude as the first-order (or main) effects (3 and -3) so it is a major feature of the profiling.
A significant interaction effect means that the effect of one factor (discount) depends on the level of another factor (direct_comm).
- There is practically no effect of changing discount when direct_comm is 1.
- There is practically no effect of changing direct_comm when discount is 0.
- There is a strong effect of changing discount when direct_comm is 0.
- There is a strong effect of changing direct_comm when discount is 1.
This case illustrates why interactions in the response are so important to modeling and prediction. The Prediction Profiler is a great way to understand and exploit interaction effects.
