What is the PASRR definition of intellectual disability?
According to 42 CFR 483.102(b)(3), an individual has an intellectual disability if he or she has:
A level of intellectual disability as described in the American Association on Mental Retardation's (AAMR) Manual on Classification in Mental Retardation, published in 1983; or
A related condition, which is defined by 42 CFR 435.1010 as a disability that:
a) Is attributable to:
i) Cerebral palsy or epilepsy; or
ii) Any other condition, other than mental illness, found to be closely related to intellectual disability because it impairs intellectual functioning or would require services normally delivered to an individual with impaired intellectual functioning;
b) Manifests before the age of 22;
c) Is likely to continue indefinitely; and
d) Results in substantial functional limitations in three or more of the following life activities:
ii) Understanding and use of language;
v) Self-direction; or
vi) Capacity for independent living
The CFR cited the AAMR's 1983 Manual because it represented the most current understanding of intellectual disability at the time the regulations were published, and because the authors of the original PASRR legislation (in the Omnibus Budget Reconciliation Act of 1987) wished to identify a set of people that would not change over time (so that the application of PASRR would itself not change arbitrarily). Nonetheless, it is very much "of its time."
Notions of intellectual disability have evolved considerably since 1983. Indeed, the Association itself has published several revisions to the manual, and has changed its name to The American Association of Intellectual and Developmental Disabilities (AAIDD), reflecting a move away from the (now derogatory) term "mental retardation."
Identifying related conditions may involve some discretion on the part of a clinician or evaluator. However, although related conditions are treated by PASRR as a subset of intellectual disability, note the definition of related condition does not require that an individual have an intellectual disability so long as other related conditions criteria are met.
For reference, this page includes a copy of the 1983 Manual as a downloadable PDF below.