For disability purposes, what you have to prove at a hearing is the same regardless of whether the case concerns SSI or Disability: you still have to go through the five-step sequential evaluation process. The programs differ in their technical requirements for disability.
Supplemental Security Income benefits (SSI) is a disability program for those who have little or no income or resources, except for an automobile, a home and furnishings, and are disabled. It pays a flat rate called the Federal Benefit Amount (FBA) which in 2009 is $674 per month. It pays nothing for dependents of the disabled. If you receive either money (earned or unearned) from any source, or assistance in the form of food, clothing or shelter, that amount may be reduced.
Disability Insurance benefits (DIB) is a disability program for persons who have worked and paid Social Security Taxes for 20 out of the last 40 quarters, generally speaking, and are disabled. It also pays for dependents of the disabled to a certain extent. The amount of DIB is computed based upon average monthly earnings according to a computer program created by Social Security, and is unaffected by any other income you might get. If you are eligible for both types of Disability benefits—as some of my clients are—your payments will be subject to a complicated formula called the Windfall Offset, which reduces your SSI payments by the amount that should have been paid had the DIB been paid first.