In the United States and Canada, many nurses who choose a specialty become certified in that area, signifying that they possess expert knowledge. There are over 200 nursing specialties and subspecialties. Studies from the Institute of Medicine have demonstrated that specialty-certified nurses have higher rates of patient satisfaction, as well as lower rates of work-related errors in patient care. Registered nurses (RNs) are not required to be certified in a certain specialty by law. For example, it is not necessary to be a certified medical-surgical registered nurse (CMSRN) (a medical surgical nursing certification) to work on a medical-surgical (med-surg) floor, and most med-surg nurses are not CMSRNs. Certifications do, however, instill professionalism and make the nurse more attractive to prospective and current employers. Certified nurses may earn a salary differential over their non-certified colleagues, but this is rare. Some hospitals and other health care facilities are willing to pay a certified nurse extra when he or she works within their specialty. Also, some hospitals may require certain nurses, such as nursing supervisors or lead nurses, be certified. Certification instills confidence in the nurses. Magnet hospitals advocate certifications.