5.
Process Improvement
5.5. Advanced topics 5.5.9. An EDA approach to experimental design 5.5.9.9. Cumulative residual standard deviation plot


Graphical representation of extrapolation 
Extrapolation is performed similarly to
interpolation. For example, the predicted
value at temperature T = 375 and time t = 28 is
indicated by the "X":


Pseudodata 
The predicted value from the modeling effort may be viewed as
pseudodata, data obtained without the experimental
effort. Such "free" data can add tremendously to the insight via the
application of graphical techniques (in particular, the
contour plots and can add significant insight
and understanding as to the nature of the response surface relating
Y to the X's.
But, again, a final word of caution: the "pseudo data" that results from the modeling process is exactly that, pseudodata. It is not real data, and so the model and the model's predicted values must be validated by additional confirmatory (real) data points. A more balanced approach is that:


Summary  In summary, the motivation for model building is that it gives us insight into the nature of the response surface along with the ability to do interpolation and extrapolation; further, the motivation for the use of the cumulative residual standard deviation plot is that it serves as an easytointerpret tool for determining a good and parsimonious model. 