That only normalizes natural variances in your patients, not artificial biases introduced by the healthcare system. Pump and other hardware measuring out dosage

That only normalizes natural variances in your patients, not artificial biases introduced by the healthcare system. Pump and other hardware measuring out dosages might come from different manufacturers or be calibrated and serviced by different technicians. Maybe the study includes one too many hospitals in a region dominated by one manufacturer whose hardware tends to error more in one direction than other manufacturers. The generics used by pharmacies and hospitals might be slightly different because of local relationships. Exercise, ability to have visitation in quarantine, and other amenities in hospitals will have differing impacts on confounding factors like exercise and morale. And on and on. There are a bunch of "contract research organizations" all over the world, quite a few of them making billions of dollars a year, who specialize only in running clinical trials because these things are so complicated. The documentation for clinical trials are often thousands of pages long describing tiny details like device calibration across hospitals trying to eliminate as many risks as possible. These organizations tend to have long standing relationships with hospitals and host many different trials in each one with a bunch more subcontractors who do patient selection.