Answer: All have low incomes.
Step-by-step explanation:
The Supplemental Security Income program is a federal program that is meant to alleviate the suffering of citizens(and certain foreigners) with low income who are old, disabled or blind.
The requirements as already mentioned, are that the person either be blind, elderly (at least 65) or disabled. The one thing that they must all have in common however, is that they have low incomes and therefore are unable to sustain their needs.