Final answer:
Physicians with a set fee contract for services to a plan's subscribers are part of a Health Maintenance Organization (HMO), which pays a fixed amount per enrolled person rather than per service, but may encounter adverse selection in the insurance market.
Step-by-step explanation:
A group of physicians who have a contract to provide services to subscribers of a plan for a set fee are part of a Health Maintenance Organization (HMO). In an HMO, providers are paid a fixed amount per person enrolled, regardless of how many services each person uses. This is in contrast to a fee-for-service system where providers are reimbursed based on the individual services they provide. An HMO aims to focus on prevention and efficient care to reduce overall costs. However, this system can lead to issues such as adverse selection, where insurance buyers with more health risks are more likely to opt-in for the insurance, perceiving it as a good deal, while healthier individuals might opt-out due to the cost.