Patient preferences have to be taken into consideration, too. Medical decisions necessarily involve value judgments, and who better to make those decisions than the patient? If a fashion model doesn’t want curative surgery because it will scar her face, that may make sense in the context of her priorities. As a doctor, I may not agree with her, but I have to try to understand her reasoning and abide by her decision.

The weaker a treatment recommendation, the more patient preferences should enter into medical decision making, and the more variation you should expect to see. This is a basic conflict in modern medicine: treatment uniformity, which aims to optimize population health, versus treatment variation, which aims to respect individual choice. There is no obvious solution to this conflict, but the resolution will determine what medical care is going to look like in 10 or 20 years.

After spending nearly two decades in medicine, I am still amazed by how spare the evidence is on which we doctors base our medical decisions. Treatment guidelines, often accompanied by a de facto mandate, are frequently reversed.

Only a few years ago, for example, beta-blocker drugs were routinely recommended for almost all patients undergoing noncardiac surgery. Since then, research has shown that these drugs may significantly increase the risk of stroke at the time of surgery. I remember colleagues questioning the beta-blocker recommendation for certain patients and being admonished for not being “evidence-based.” I shudder to think how many patients were left disabled by strokes because of the blanket adoption of this standard.

What is in vogue today is often discarded tomorrow. Hormone replacement therapy for women after menopause is an example of a once widely implemented treatment that we have now largely abandoned. In September, in response to new research, the American College of Cardiology revoked a major recommendation on heart-attack treatment. “Science is not static but rather constantly evolving,” said its president, Patrick T. O’Gara, in explaining the decision.