Specific ailments are too numerous to list in this venue, but they are divided into adult disabilities and childhood disabilities, with considerable overlap. These ailments are catalogued as a Listing of Impairments, which is subdivided in adult and childhood impairments by body systems. The adult system taxonomy includes musculoskeletal, special senses and speech, respiratory, cardiovascular, digestive, genitourinary, hematological, skin, endocrine, multi-system, neurological, mental, malignant-neoplastic and immune system. The childhood listing includes all these, as well as growth impairment disorders.
For each system-category, the Social Security Administration publishes a list of causes, which is nearly all-inclusive, and a definition of qualifying ailments based on a descriptive account of loss of function. The loss of function determines eligibility. The categories of illness and injury associated with loss of function are listed and numbered for cataloguing and administrative purposes, for example, under musculoskeletal (1.00) are "disorders of the spine" (1.04) and "fracture of an upper extremity" (1.07). Applicants for disability benefits will need to use these numerical identifiers in their applications.
The ailment itself is not what qualifies the claimant for benefits under SSDI, which are paid according to work history. The impact of the ailment is the final determining factor for approval of claims. Impact is determined by severity in the first case. The ailment or injury must be severe enough to prevent the claimant not only from doing his past job, but it must also effectively prevent the claimant from finding new employment consistent with age and experience. The severity of the ailment must also sustain this unemployable condition for at least 12 months for the applicant to qualify for benefits.
Qualification for SSI is far more restricted. SSI benefits are means tested and are not indexed to work history. SSI benefits can only be paid to those who are 65 years old or older. Recipients must be legally blind or otherwise disabled. Proof must be provided to the Social Security Administration that the claimant's assets, including family income and investments, amounts to less than $3,000 (as of March 2011). This is not monthly or annual income, but total assets.
Denial rates for first time applicants, as of 2010, were 60 percent. Denial rates for appeals were 80 percent. The most common reason for denial is lack of documentation. Applicants must present enough documentation of doctor's visits, tests, therapies and medications to prove to a disinterested reader the severity of the ailment or injury and include statements from physicians that the ailment will result in disability for at least 12 months. Many applicants have found that hiring an attorney substantially increases the probability of approval.