This is what I am doing:
1. I run a "Fit Curve" analysis of non-linear data using both a Grouping variable and a By variable (there are 5 of these)
2. Then apply a "Fit Logistic 4P" to the Fit Curve analysis
3. Then "Save Parameter Prediction Formula"
--> this step saves two items to a new column in my data table, (1) a Formula that I fully understand and (2) a "By ID" column property that I don't understand.

Does anyone know that this "By ID" column propery is and what does it represent? If seems to have a single large integer in it.
Thank you