More studies of this type are being done as the number of health care dollars shrinks. Sometimes it's hard to compare patients because there are so many variables from patient to patient. A recent study of patients with disc-related back pain looked at one measure called the straight leg raise (SLR) test.
The private insurance company requires a positive SLR test before treatment is approved. They found some patients were up to 100 times more likely to have a positive SLR test if they were covered by a private manage care service. This was compared to patients in a worker's compensation program where prior authorization isn't needed.
It's not clear yet whether the difference is related to the patient's health, doctor's exam, or insurance coverage. Maybe it's some other factor altogether. More studies are underway to take a closer look.