Final answer:
The primary criterion for Medicaid enrollment is income, with the program designed to aid low-income individuals and varying by state. While the largest enrolled group is children, most of the spending is directed towards the blind or disabled, and the elderly.
Step-by-step explanation:
The primary criterion for Medicaid enrollment is income. Medicaid is a federal-state joint program focusing on providing medical insurance to low-income individuals, including those near the poverty line and those below it. Populations primarily covered include low-income families with children, the low-income elderly, and people with disabilities. The Medicaid program varies by state, with different eligibility criteria that could make someone eligible in one state but not in another. Furthermore, children are the largest group enrolled in Medicaid; however, the majority of Medicaid spending goes towards those who are blind or have a disability, followed by the elderly, despite children constituting the largest demographic covered.