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fibrillation is even more complicated because accurate information about the first part of the formula, the probability of an outcome, is not available for an individual; it is available only for groups of patients. For example, age, gender, genetics, lifestyle, diet, concurrent medical conditions, and a host of other variables all influence the probability of stroke or hemorrhage while on anticoagulation treatment. Dr. Liana Fraenkel and Dr. Terri Fried of the Yale School of Medicine wrote an insightful article on how hard it is to give individual patients with atrial fibrillation accurate information on their risk of bleeding from anticoagulation treatment. This is particularly true for the elderly or those who have coexisting common medical problems, like diabetes, kidney disease, and difficulty with balance, because the data on risks and benefits of anticoagulation come from studies that typically exclude these kinds of patients: Liana Fraenkel, Terri R. Fried, “Individualized medical decision making ,” Archives of Internal Medicine 170 (2010), pp. 566–569.

61 Number needed to harm is discussed in Finlay A. McAlister et al., “Users’ guides to the medical literature. Integrating research evidence with the care of the individual patient,” JAMA 283 (2000), pp. 2829–2836; Finlay A. McAlister, “The ‘number needed to treat’ turns 20—and continues to be used and misused,” CMAJ 179 (2008), pp. 549–553.

61 The study on physician and patient assessment of when to be treated for high blood pressure: Finlay A. McAlister et al., “When should hypertension be treated? The different perspectives of Canadian family physicians and patients,” CMAJ 163 (2000), pp. 403–408.

62 Hypertension guidelines and cutoffs are found in Avram V. Chobanian et al., “The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 Report,” JAMA 289 (2003), pp. 2560–2572; Giuseppe Mancia et al., “2007 Guidelines for the Management of Arterial Hypertension: The Task Force for the Management of Arterial Hypertension of the European Society of Hypertension (ESH) and of the European Society of Cardiology (ESC),” Journal of Hypertension 25 (2007), pp. 1105–1187. See also Hector O. Ventura, Carl J. Lavie, “Antihypertensive therapy for prehypertension: Relationship with cardiovascular outcomes,” JAMA 305 (2011), pp. 940–941. Numbers relevant to Alex Miller’s case: One first should distinguish between the absolute benefit versus relative reduction with treatment. Mild hypertension with a diastolic reading of 90 to 100, based on seventeen controlled trials, with most people younger than sixty-five years old, showed a 16 percent relative reduction in coronary events and a 40 percent relative reduction in stroke. But the absolute benefit is related to the predicted number of cardiovascular complications. You need to treat four to five years to prevent a coronary event in 0.7 percent of patients and prevent a stroke in 1.3 percent of patients, for a total of 2 percent, with a decrease in mortality of 0.8 percent. So to calculate the number needed to treat, you need to treat one hundred patients with antihypertensive medication for four to five years to prevent cardiovascular complications in two of them. Flipping the frame, this means that ninety-eight people do not benefit from the therapy out of one hundred treated. Systolic hypertension is most relevant to the elderly, where it’s often an isolated finding without elevation in the diastolic reading. Here, you need to treat eighteen older patients for five years to prevent a cardiovascular complication in one, meaning that seventeen of eighteen people who are elderly treated with medication do not clearly benefit. An excellent overview of patients’ understanding these data and making choices for therapy of hypertension: H. Gilbert Welch, Overdiagnosed : Making People Sick in the Pursuit of Health (Boston: Beacon Press, 2011). It is noteworthy that Europeans have a different definition of what hypertension is, with cutoffs that are 5 to 10 millimeters