Why is there no power estimate for the last category of categorical variables?

LEP

In Evaluate Design > Power Analysis, why is there no power estimate for the last category of categorical variables? For example lets lay you have a categorical variable X with three categories.  The resulting power analysis for an experiment will provide a Power for X 1 and X 2 but not X 3.  Why is that and how can I find out what it is?

Mark_Bailey

JMP uses the effect parameterization for categorical predictors in the linear predictor. That parameterization means for a k-level predictor, only k-1 parameters are estimated. All k parameters must sum to zero, so the first k-1 estimates are free but the last parameter is fixed to be -1 times the sum of the first k-1 parameter estimates.

 

Since there is not estimate, there is no test. If there is no test, then there is no meaning to power.

 

 

This simple case with a single categorical factor with 3 levels illustrates your situation and what I explained. Note that JMP also reports the power for the whole term as well as for individual parameters that make up a term. I find this useful because I think in terms of effects, not levels.