I have just found out that I had made a huge mistake on how I should approach this kind of study design, apart from being called Derivation cohort and Validation Cohort all the data should be in one data set whereas before I treated them as separated data sets, this made me crazy.
I had to use Excel, this involves making a new column and using the RAND formula to randomly select the rows, sort them from lowest to highest values according to the random numbers in the new column, then make categories by assigning 2/3 of the data as Derivation (0) and 1/3 as Validation (1). Making the two groups comparable. then I had to import my data back to JMP.
As I did this on excel, I think it's possible to be done on JMP without getting troubles, I will go through the discover JMP and Tutorials to find for myself.
I'm sorry for my inconvenience, I hope this will be helpful to others.
thank you
@txnelson and
@P_Bartell