Square test not available when expected (Q775)

The information in this article applies to: 
MODDE 12
MODDE 11
MODDE 10
Symptoms: 

In the Analysis Wizard, on the Coefficients page, the Square test button is unavailable even though adding a square increases the Q2 with more than 0.05.

Cause: 

When there are qualitative factors in the model, the square test fails.

In MODDE 10, the Square test is also always performed using the linear model, even if the current model includes interactions. Occasionally adding an interaction term reduces the residuals significantly, which in turn may lead to that the addition of a square term improves the model significantly.

Status: 

The Square test rules will be evaluated.

More Information: 

Similar situations may occur for the Interaction test, also performed on the linear model.

Date modified: Feb 21, 2017
Article type: 
Problem