When I was a resident in emergency medicine, I spent many hours uncovering the identities of John Doe and Jane Doe patients who were unconscious, disoriented, or mute. I searched their belongings for receipts that included an address or scanned their clothing labels for a clue. Sometimes this worked. Often, hours or days passed before a family member was found who knew the patient's medical history and health care preferences. By that time, substantial worry had been endured, and often possibly unwanted medical interventions had occurred.Today, I lead the information-technology efforts at an academic health center, and I have . . .