Researchers analyzed 1,057 audiotaped encounters between primary care doctors and surgeons and their patients.
The cases involved such as decisions as whether to have a lab test to check thyroid hormone level and whether to have laboratory prostate-cancer screening.
"Primary care physicians frequently made decisions without discussing the intervention with the patient or seeking their involvement," the researchers reported in Wednesday's Journal of the American Medical Association. "These findings suggest that the ethical model of informed decision-making is not routinely applied in office practice."
The researchers were led by Dr. Clarence H. Braddock III of the University of Washington in Seattle.
Something important was missing from discussions 91 percent of the time, such as talking about the pros and cons of a decision, researchers said. For example, a doctor might fail to say that a higher dose of a drug could offer better blood pressure control but also cause fatigue.
The researchers noted that the doctors, 59 general internists and family practitioners and 65 surgeons, may not have been representative, since they were mostly white men chosen from databases of physician-controlled insurance companies in Colorado and Oregon.
Also, a situation may have improved since 1993, when the audiotapes were recorded for a study of doctor-patient communication and malpractice claims, the researchers said.
But an expert who was not involved in the study said the results were so extreme that they probably apply to doctors on the whole and probably persist.
"New strategies, including more effective and efficient use of educational materials and decision aids in office practice, will need to be developed and tested as part of the solution," Dr. Michael J. Barry of Massachusetts General Hospital in Boston said in the editorial.