Final answer:
The eligibility for group health insurance is predominantly determined by one's employment status, as this allows for a diverse risk pool and helps insurance companies mitigate the risk of adverse selection.
Step-by-step explanation:
The eligibility of members for group health insurance in the United States is typically determined by employment status. Group health insurance is primarily available to employees through their employers and is designed to mitigate adverse selection by pooling a diverse group of individuals together. This includes people with varying health risks, which balances the risks for the insurance company. Under the Patient Protection and Affordable Care Act, the health exchange markets also facilitate selling health insurance to a broad population, mandating coverage and preventing discrimination based on pre-existing conditions. The emphasis is on providing systems that expand coverage, rather than selecting individuals based on health statements or underwriting processes.