The independent variable (or predictor, feature, or factor) is represented by a data column in your data table. Try this:
- Select Analyze > Fit Model.
- Select the column for the independent variable.
- Click Add. (Note that you can make any linear predictor that you might need using Add, Cross, or one of the Macros with the Degree value.)
- If this term is meant to be a random effect, then select it in the Effects list, click the red triangle next to Attributes, and select Random.
This sequence will force JMP to use REML to estimate the parameters including the variance components.