Dec. 8, 2021 In the sequential evaluation of disability by the Social Security Administration (SSA), a major step is whether the individual has a condition that meets the twelve-month duration requirement and that is represented on the Social Security Administration's Listing of Impairments (LOI) or equal to a listed impairment. The LOI is divided into two parts. One part applies to individuals over age eighteen and one part is applicable to individuals under eighteen. The LOI includes fifteen major body categories: growth impairment, musculoskeletal system, special senses and speech, respiratory system, cardiovascular system, digestive system, genito-urinary system, hemic and lymphatic system, skin, endocrine system, multiple body systems, neurological, mental disorders, malignant neoplastic diseases, and immune system. An explanation for what is encompassed by each category is included. Within each category, impairments are given that are considered to rise to the level of "severe" such that they would prevent an individual from engaging in substantial gainful activity. A diagnosis falling within the parameters of the LOI must be established by medical evidence obtained through objective clinical and laboratory techniques. In many instances the required medical evidence is stated in the LOI. Absent appropriate medical evidence, a diagnosis of an impairment will not be found to appear on the LOI. Included with the other information present, the LOI sometimes states the symptoms usually associated with certain listed impairments. Even though an impairment is not specifically listed on the LOI, the SSA authorizes impairments that are the medical equivalent to a listed impairment. The medical evidence received to establish a medical equivalency is given varying weights based on the source of the evidence. For example, the medical opinions of state agency doctors and psychologists are accorded the weight of nonexamining doctors and psychologists. These opinions can be accorded greater weight if based on, for example, the complete case file that includes a medical report from a specialist in the individual's area of impairment. The opinion of a doctor or psychologist who has been appointed by the SSA Commissioner is given the weight of an expert opinion.