A recent study by the Mayo Clinic found that more than 20 percent of patients who sought a second opinion had previously been misdiagnosed by their primary care physician. During the two-year study, researchers examined the records of 286 patients who had seen primary care physicians, physician assistants and nurse practitioners in 2009 and 2010. Nearly two-thirds of the patients were under the age of 64, and the majority of patients were female. After receiving an initial diagnosis, each patient sought a second opinion from the Mayo Clinic's General Internal Medicine Division. Of the 286 patients, only 36 patients (12 percent) had received confirmation that the original diagnosis was complete and correct. In 63 cases (21 percent), the diagnosis was completely changed meaning the patient had been misdiagnosed by their primary care physician. In the remaining 188 cases (66 percent), patients received a refined or redefined diagnosis. Researchers did not find any significant differences between provider types.