Physician assistant education is based on medical education although unlike medical school which lasts four years plus a specialty-specific residency, PA training is usually 2 to 3 years of full-time graduate study like most master's degrees. The training of PA education consists of classroom and laboratory instruction in medical and behavioral sciences, such as anatomy, microbiology, immunology, pharmacology, pathophysiology, hematology, pathology, genetics, clinical medicine, and physical diagnosis, followed by clinical rotations in internal medicine, family medicine, surgery, pediatrics, obstetrics and gynecology, emergency medicine, and geriatric medicine, as well as elective rotations. Unlike physicians, who must complete a minimum of three years of residency after completion of medical school, PAs are not required to complete such residencies after they complete their schooling. There are residency programs in certain specialties for PAs who choose to continue formal education in such a format.