Hi @clee,
Please also see this post for more information about IOV in Pumas:
For your data set, you will want to have a single OCC column with 1-4/5 for each cycle of dialysis.
Regarding your 2), if I understand you correctly, you may want to do something like the choose_covariates
function here: https://tutorials.pumas.ai/html/simulation/simulating_populations.html . So, you’ll determine each subject’s OCC column based on whatever criteria you choose for that given subject, and then pass OCC as a covariate.