An estimated 1.2 million adults in the United States have been diagnosed with intellectual disability, which is a disability characterized by significant limitation in both intellectual abilities and everyday functioning. According to the American Association on Intellectual and Developmental Disabilities (AAIDD), intellectual disabilities are “characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills.” This definition of an intellectual disability is generally consistent across different diagnostic classification systems, including the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) and International Classification of Diseases (ICD). Although intellectual disabilities originate before the age of 18 years, their impact is lifelong. For adults with intellectual disability, accurate and comprehensive assessments of their functioning can be ...