Countries With National Health Insurance Eliminate Unnecessary Medical Care.
A frequent criticism of the U.S. health care system is that it is wasteful because a considerable number of procedures are "unnecessary." For example, Dr. Robert Brook of the Rand Corporation maintains that "perhaps one-fourth of hospital days and two-fifths of medications could be done without." 
One source of evidence for unnecessary medical care is a series of studies that show wide variations in the rate of treatment among different U.S. communities, with no apparent justification. Another major study of unnecessary medical procedures, conducted by the Rand Corporation, concluded that 40 percent of medical procedures were inappropriate" or "questionable." 
One might suppose that in countries where health care is rationed and many medical needs are unmet, doctors would tend to provide only "necessary" care. That turns out not to be the case. As in the United States, considerable variation in treatment rates exists in countries with socialized medicine. For example, in Britain there are widespread differences in the referral (to specialists) rates of general practitioners and in their prescribing habits:
One study found a four-to-one difference in the number of prescriptions per patient among British doctors, and for prescriptions to treat specific diseases the differences were even greater. 
The difference in the rate at which British general practitioners refer patients to hospital specialists varies by at least four to one – according to one study by 25 to one – and there is a high correlation between referrals and subsequent hospital admissions. 
Figure VIII shows that the practice patterns of physicians vary widely in Canada as well. For example:
There is a four-to-one difference among Canadian counties in the rate of cesarean sections.
There is a four-to-one difference in rates of tonsillectomy and hysterectomy and a twoto-one difference in the rates of mastectomy, prostatectomy and cholecystectomy.
Figures IX and X compare the rates for surgeries for which it is believed that doctors exercise a great deal of discretion. There is no common pattern except that British rates are generally lower – as they are for almost all types of surgery.
Close inspection of the Rand study reveals the major reason why there are such variations in medical practice in the United States: doctors frequently do not agree on what should be done and there is often no objective, "right" answer. Indeed, when the Rand researchers went to great lengths to get consensus, a panel of experts was able to agree on a procedure's appropriateness less than half the time.  Medicine, it seems, is often more art than science.
Interestingly, the panel did agree that 12 percent of the time certain procedures were clearly inappropriate. But the cases studied were in the early 1980s, and undoubtedly less inappropriate medicine is practiced today. The reason is that the United States has devoted considerable resources to monitoring the behavior of physicians to high-quality care. Most countries with national health insurance have done little along these lines.