Final answer:
In an HMO, the Utilization Reviewer monitors patient services to ensure necessary and efficient care in line with the fixed payment healthcare model, which aims at cost-effectiveness and quality maintenance.
Step-by-step explanation:
Within a Health Maintenance Organization (HMO), the individual usually assigned to monitor services provided to the patient, both inside and outside the facility, is known as the Utilization Reviewer. The Utilization Reviewer is responsible for ensuring that healthcare services are necessary and efficient, thereby addressing the moral hazard that can occur when patients demand more care than necessary or when providers offer unnecessary services in a fee-for-service system. This role is critical in the HMO model, where the incentive is to provide cost-effective care while maintaining quality, given the fixed amount paid per patient enrolled.