The elderly man was emaciated, so hospital physicians were running a series of tests for cancer, a common cause of weight loss in older patients.Saul Weiner, MD, suspected something else might be going on. "Where are you living?" he remembers inquiring. "I move around a lot," the haggard man responded. Weiner then asked if his patient was eating regularly. Sometimes, but not every day, the man admitted. A diagnosis snapped into focus: The disheveled patient was homeless and starving. Weiner canceled the medical tests and called in a social worker. The experience at a Chicago hospital several years ago inspired Weiner to study what he calls "contextual errors," or the failure by doctors to consider an individual's social or economic circumstances when diagnosing illness or prescribing treatment. Weiner arranged to send actors playing patients into physicians' offices and discovered that errors occurred in 78% of cases when socioeconomic concerns were a significant factor, according to a paper published Monday in the Annals of Internal Medicine.