Drug companies seeking regulatory go-ahead for a new medicine have to collect a prodigious quantity of evidence.
By contrast, introducing a new surgical technique could hardly be simpler. You just, well, do it.
The latest clinicians to draw attention to this anomaly are Professor Charles Warlow, president of the Association of British Neurologists, and Dr Peter Rothwell, a Medical Research Council research fellow at Oxford's Radcliffe Infirmary.
Their target was the latest interventional procedure for preventing stroke, and their forum was the recent World Congress of Neurology.
One of the causes of stroke is a narrowing of the carotid arteries, the vessels in the neck that carry blood to the brain. It is 50 years since surgeons devised an operation to clear these blockages and restore the blood flow to normal. Unfortunately, it was several decades before clinical trials established the true value of the procedure. These showed that only patients with severe and recent narrowing benefited. In other words, many people had undergone this relatively risky operation for nothing.
What the two neurologists fear is a re-run of this sequence of events with another increasingly popular procedure, carotid angioplasty. This uses a small balloon on the end of a thin tube inserted at some remote part of the body, then pushed under x-ray guidance through the blood system until it lies within the narrowed region of the artery.
As in the already well-established coronary angioplasty, the balloon is then inflated to restore the vessel to its original width.
Warlow and Rothwell argue that carotid angioplasty should only be done on patients who are enrolled in clinical trials. Unless this happens, they say, 20 years from now the NHS may once again find that resources have been wasted, and many patients' lives put at risk for little or no benefit.