- how to treat IVs that are high-level (n-arms) but not relevant as input for the theorist - how to turn high-level IVs into low-level IVs (experimental design) - how to treat observations (e.g., participant age) which may be inputs for the theorist (and treated as IVs) - high-level IVs: should they get their own data table since they are the only ones used in the experimentalist