Interaction in a Two-Factor Regression Model
This Demonstration considers the effect of interaction in a two-factor factorial experiment.[more]
A regression model representation of a two-factor factorial experiment can be written as
where represents the response, factor 1, factor 2, the s are parameters with values to be determined and is a random error term.
If you increase the value of the interaction coefficient , the twisting of the response surface increases . This is most apparent in the curvature of the contour lines in the 3D and contour plots.[less]
 D. C. Montgomery, Design and Analysis of Experiments, 9th ed., Hoboken, NJ: John Wiley & Sons, 2017.