In addition, a growing number of centers (18-20%) are now run by hospitals or doctor groups, who use or employ their own center and administrative personnels or make use of existing company centers to serve the employee population. Lastly, an increasing variety of companies are taking part in shared, multi-employer centers, situated either on one company's area or centrally situated.The supplier will construct, personnel and handle the facility either at the demand of a group of employers or will solicit employers in a defined geographical location. Despite the model used, it's essential that employer remain engaged in supplier selection, center oversight, strategic and policy instructions. Staffing practices vary from one onsite center to another, though over 60% of centers are led by a Nurse Professional or Physician's Assistant.