For most medical treatment decisions, there is more than one reasonable choice. Although bacterial meningitis needs antibiotics, decisions about treatments for conditions such as clinically localized prostate cancer have many options, including observation, radiation therapy, and surgery. In turn, each of these broad treatment categories has variants: watchful waiting, active surveillance, brachytherapy, external beam radiotherapy, open surgery, and laparoscopic robotic-assisted surgery. Evidence about comparative effectiveness of these treatments is available but limited, and the preferences of informed patients vary. For such preference-sensitive decisions, geographic practice variation is the rule, reflecting physician more than patient preferences.1 For example, in a report2 from the Dartmouth Atlas of Health Care, population-based rates of radical prostatectomy for prostate cancer among men in 306 US hospital referral regions ranged almost 10-fold from 2007 to 2012, from a low of 0.5 to a high of 4.7 per 1000 male Medicare beneficiaries aged 65 to 75 years. Shared decision making, in which patients and physicians collaborate to make decisions about preference-sensitive treatments, has been proposed as an approach to reduce unwanted practice variation, but maintain desirable variation, by tailoring decisions to patients’ clinical characteristics and informed preferences.