Final answer:
States can opt to receive federal Medicaid funds for additional optional populations besides the mandatory groups by expanding Medicaid coverage, which typically includes more low and moderate-income adults. The extent of the optional populations covered varies by state.
Step-by-step explanation:
The optional populations for which states may receive federal Medicaid funds, in addition to mandatory groups like children, the blind, and the disabled, depend on each state's eligibility standards. Under the Medicaid Expansion initiative, part of the Affordable Care Act (often referred to as "Obamacare"), states were encouraged to expand their Medicaid coverage to include more low and moderate-income citizens. The expansion aimed to provide broader healthcare access and incentivize those receiving welfare to enter the workforce. As a result, states that have opted into the expansion have a more considerable portion of low-income adults covered, whereas eligibility can vary widely from state to state based on each state's established criteria.
According to the available data, as of 2014, approximately 69.7 million people were enrolled in Medicaid. Almost half of these enrollees are children, representing the largest percentage of populations using Medicaid at 47%, followed by adults at 28%, and finally the blind and disabled at 16%. Despite children being the largest group covered, Medicaid spending is primarily directed towards the blind and disabled (44%), and the elderly (20%), with children receiving only 21% of the expenditures.