The output indicates that the regression equation is in coded units when the model is nonhierarchical. For more information on hierarchy, go to What are hierarchical models?.
Use the regression equation to describe the relationship between the response and the terms in the model. The regression equation is an algebraic representation of the response surface.
The first-order regression equation with more than one term takes the following form:
If the response surface contains curvature, then a polynomial model of higher degree is used. The second-order model is:
In the regression equation, the letters represent the following:
- y is the response variable
- b0 is the constant
- b1, b2, ..., bk are the coefficients
- X1, X2, ..., Xk are the values of the terms
- ε is the error term
For a regression equation in coded units, the low level of a factor is −1 and the high level of a factor is +1. Because the equation is averaged over blocks, no coefficients for any blocks are in the equation.