SAS will hold the last level of the categorical variable and will not give an estimate. I know that this is the intercept.

My question is how to calculate the interaction of the continuous variable with the 3rd level of the categorical variable that I don't get an estimate?

PHP:

```
Effect increment Estimate Standard Error
Intercept 10.8879 51.1246
x 0.003093 0.0658
y -0.3009 2.0023
increment one 65.6866 12.3805
increment two -30.1428 12.3987
increment three 0 .
x*increment one -0.09041 0.01706
x*increment two 0.0387 0.01709
x*increment three 0 .
```