Minding your P's and M's

In medicine, internists need to mind not just their "P's and Q's" but their "P's and M's," that is, evidence-based practice and evidence-based medicine.


Explanations abound for the origin of the expression "Mind your P's and Q's." One is that these letters, in lowercase, easily could be confused by 19th-century typesetters; "p" and "q" look so much alike. Another is that "P's" sounds like "please" and "Q's" sounds enough like rapidly and repeatedly spoken "thank you's" to have "mind your P's and Q's" stand in for "mind your manners." My favorite explanation, of course, traces the expression back to 17th-century English pubs where, by the end of the night (or would it be the next morning?), customers would have to settle up and pay for their consumed pints and quarts. Let's go with that one.

In medicine, we need to mind not just our "P's and Q's" but our "P's and M's," that is, evidence-based practice (EBP) and evidence-based medicine (EBM). No one was more aware of this distinction than the late David L. Sackett, MD, whom we lost two years ago. An American by birth but a Canadian (and Englishman) by choice, Dr. Sackett taught us all about evidence-based medicine. That he disavowed credit for popularizing it, pointing out instead that it was an old concept, was typical of him, modest to a fault. He was wrong, of course. Along with his colleague Gordon H. Guyatt, MD, FACP, Dr. Sackett deserves credit for so much of what is now embraced within evidence-based medicine, including:

  1. 1. basing diagnoses on the best possible evidence, typically well-crafted randomized controlled trials (RCTs) or better still, meta-analyses of multiple RCTs organized into systematic reviews;
  2. 2. critically interpreting the medical literature to allow for appraisal of the worth of diagnostic tests and treatments; and, finally,
  3. 3. shining light on hidden biases in research.

This was all being worked out in the '70s and '80s, just as my formal training was completed. I had to learn this—so I could teach this—on my own, in an environment that was not always welcoming to evidence-based medicine. I recall one of internal medicine's leading figures referring to those "EBM guys" as "evidence-based police." But this particular luminary did not understand what Dr. Sackett understood and what he clarified in his later writings: that there is a difference between evidence-based medicine and evidence-based practice.

What is the difference?

In a personal conversation that I had with Neil J. Stone, MD, MACP, who led the American Heart Association/American College of Cardiology (AHA/ACC) panel that wrote the recent evidence-based "Guidelines on the Treatment of Blood Cholesterol to Reduce Atherosclerotic Cardiovascular Risk in Adults," he credited Dr. Sackett for the model that places evidence-based practice, not evidence-based medicine, at the center of the medical decision-making process. This process is informed by best research and evidence, but also by clinical expertise—that is, a physician's knowledge, experience, and judgment—and by a third series of factors, the patients' values and preferences. So the AHA/ACC guidelines recommend not treating individuals with hypercholesterolemia to target but, rather, selecting them based on risk-benefit groups, as this is what the scientific evidence showed. However, especially when statin therapy is being considered for primary prevention, this should be done only if it is consistent with the physician's clinical expertise, which accounts for the particularities of the patient, and the patient's values and preferences, the latter typically elicited by discussion.

As Dr. Sackett and his coauthors wrote in a 1996 editorial published in the BMJ, "Evidence-based medicine is not 'cookbook' medicine. Because it requires a bottom-up approach that integrates the best external evidence with individual clinical expertise and patients' choice, it cannot result in slavish, cookbook approaches to individual patient care. External clinical evidence can inform, but can never replace, individual clinical expertise, and it is this expertise that decides whether the external evidence applies to the individual patient at all and, if so, how it should be integrated into a clinical decision. Similarly, any external guideline must be integrated with individual clinical expertise in deciding whether and how it matches the patient's clinical state, predicament, and preferences, and thus whether it should be applied. Clinicians who fear top-down cookbooks will find the advocates of evidence-based medicine joining them at the barricades."

And probably, they would have found Sir William Osler right there with them. After all, it was he who said, "The good physician treats the disease; the great physician treats the patient who has the disease."

The College is committed to evidence-based practice, not just evidence-based medicine. While ACP guidelines represent the College's (and organized medicine's) best efforts in evidence-based medicine, they, like all guidelines, point to where the decision-making process starts, not necessarily where it ends. ACP guidelines now include a statement that clinical practice guidelines should be taken as "guides" and may not apply to all patients and all clinical situations.

Moreover, College guidelines emphasize the importance of eliciting the patient's preference. Just as the AHA/ACC guideline on the treatment of blood cholesterol recommended that decisions related to initiating statin therapy for primary prevention in a nondiabetic patient between ages 40 and 75 years be determined by a discussion between patient and doctor, even when that patient's 10-year risk of atherosclerotic cardiovascular disease exceeds 7.5%, so too do the College's recent guidelines for management of hypertension in patients over age 60, for example, advocate for that same type of discussion. ACP's Center for Patient Partnership in Healthcare is dedicated to ensuring that patients' values and preferences are central to the decision-making process and that their voices are heard. Finally, in the "Beyond the Guidelines" section of Annals of Internal Medicine, readers can find important examples of how clinical expertise can be brought to bear on research-based guidelines. All of this illuminates the important difference, but also the interdependence, between evidence-based medicine and evidence-based practice. I believe former ACP member Dr. Sackett would be pleased.

It is an honor to serve as your President this year and express my views in this column. Please let me hear from you.