I am currently performing a logit regression in SPSS. I am faced with problems when testing the linearity assumption using the Box-Tidwell approach.

I have 10 continuous variables and for each of them I have computed their Natural Logarithm. For testing the assumption, I run a logit regression with all continuous variables multiplied with their natural logarithm as independent variables + their normal form.

My problem is that SPSS cannot run this regression, and gives me the error:

*"Estimation terminated at iteration 20 because of perfect fit is detected - this solution is not unique"*

When I run the regression with less variables, I am able to get an output.

Question:

**How do I perform a Box-Tidwell regression on my 10 continuous variables in SPSS?**

Best regards

Thomas