If you are not using the centralize polynomial option, the parameters of the lower order terms become less meaningful.
The advantage of polynomial centering is that tests of main effects can be performed independently from tests of squared terms.
If you use the polynomial centering option, parameter estimates are centered and on the scale of the actual factor settings (as opposed to orthogonally coded). All continuous terms, including interactions, are centered by their means and parameters are labeled as such. Centering allows for location-invariant tests of consistency.
Note : If you do not want to center the polynomial, you can turn it off using the following method.
- [Fit Model] Platform: Uncheck Polynomial Centering from the red triangle in the upper left corner of the Model Specification dialog.
- Bivariate platform: From the report screen, select Other Fits from the red triangle and uncheck Polynomial Centering in the dialog box that appears.
FAQ # 2083
