There is quite a bit more to the issue than simply soliciting the patient's feelings on the decision, though, and research has only scratched the surface in identifying the myriad factors that impact, or don't impact, effective decision making involving you and your patient. Along with almost everything else in health care, one key driver is the fact that we simply can't afford inefficiency anymore. As Odette Callender, MD, and her colleagues point out in their article on non-adherence to glaucoma medications (p. 94), just the price of drugs not taken may be as high as $100 billion annually.
George Saba and his colleagues at the University of California, San Francisco, published an interesting study of shared decision making in the January/February Annals of Family Medicine. In it they acknowledge both the limitations of their own study and the conflicting results that have marked this area of research in its early years. Nonetheless, their work is revealing and instructive, particularly in formulating what they call four archetypes in decision making. The ideal, or full engagement, entails both the physician and the patient acknowledging that SDM occurred and their subjective assessment of the encounter was positive. The opposite is when SDM is absent and the experience is viewed negatively.
Most encounters, presumably, rate somewhere in between, and it's here that the obstacles—assumptions, fears, lack of trust, educational and language barriers and, of course, time—alone or in combination conspire to ruin the medical encounter. Frankly, it's a wonder you get anything done in 15 minutes with a patient.
SDM research has a long way to go but this is certainly an interesting contribution to what will be an increasingly important area of health-care research. It's well worth the trip online: http://annfammed.org/cgi/content/full/4/1/54