One hospital library can differ widely from another in size, collection, and scope of services depending on a number of variables, such as the type of institution, whether or not it is a teaching hospital, and whether or not it is independent or part of a health care system. Hospitals are not required by law or by the Joint Commission on Accreditation of Healthcare Organizations (Joint Commission, formerly JCAHO) to have on-site libraries or library staff. Hospitals affiliated with medical schools sometimes have their information needs served by academic health sciences libraries, which can make their resources available to hospital staff through extended licensing of electronic resources or other means of sharing resources. Some medical centers do not have in-house library staff but contract with external consultants to provide information services. That being said, the hospital staff are better served when professional library staff are available on-site to provide customized services and collections to meet the needs of patient care and research in that particular hospital. Teaching hospitals must also be able to meet the information needs of the students and the requirements of their accrediting bodies.