For many decades, the dominant approach to making decisions about treatment in the medical encounter has been one of paternalism.1^–7 In recent years this model has been challenged by doctors, patients, medical ethicists, and researchers who advocate more of a partnership relation between doctors and patients.2 8^–13 The reasons for this challenge have been described in detail elsewhere and include the rise of consumerism and the notion of consumer sovereignty in healthcare decision making; the women's movement with its emphasis on challenging medical authority; the passage of legislation focusing on patients' rights in health care; and small area variations in doctors' practice patterns that seem unrelated to differences in health status.7 Though the first three factors are seen as either contributors to or facilitators of patients' participation in making decisions about health care, the fourth highlights the imprecision or the “art” of medical care14: patients with similar clinical problems may receive different treatments from different doctors, due in part to systematic variations in practice patterns across geographical areas.14 15

The call for doctor-patient partnerships opens up options beyond paternalism for approaching the task of making decisions about treatment. But it also raises new complexities. Because a partnership between patient and doctor can take different forms, it is not intuitively apparent what this model would look like. The Oxford English Dictionary (1995) defines a partner as “a person who shares or takes part with another or others.” This definition leaves several important questions unanswered. For example, does the concept of a partnership imply that both doctor and patient need to share all parts of the decision making process? What is it that both parties are sharing, and to what degree? Who is responsible for determining if a partnership is possible and …