in the first year after infarction may be as low as 1%. Beta blockers would reduce this risk by a quarter, to 0.75%, for an absolute risk reduction of 0.25% or 0.0025. The inverse of this absolute risk reduction (that is, 1 / absolute risk reduction) equals the number of such patients we'd have to treat in order to prevent one event (in this case, to prevent one death following a mild heart attack in a low risk patient). In this case, we would have to treat 400 such patients for one year to save a single life (1 / 0.0025 = 400). An older man with limited exercise capacity and frequent ventricular extrasystoles who continues to smoke following his infarction may have a risk of dying in that next year as high as 10%. A 25% risk reduction for death in such a high-risk patient generates an absolute risk reduction of 2.5% or 0.025, and we would have to treat only 40 such individuals for one year to save a life (1 / 0.025 = 40). These examples underscore a key element of the decision to start therapy: before deciding on treatment, we must consider our patient's risk of the adverse event if left untreated. For any given RRR, the higher the probability that a patient will experience an adverse outcome if we don't treat, the more likely the patient will benefit from treatment, and the fewer such patients we need to treat to prevent one event. Thus, both