ABSTRACT
According to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association [APA], 2013) intellectual disability (ID) and autism spectrum disorder (ASD) are neurodevelopmental disorders with onset occurring from birth to early childhood. Three criteria define a diagnosis of ID: (1) deficits in intellectual functioning (e.g., reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning for experience) confirmed by both clinical assessment and individualized standardized intelligence testing; (2) deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility and limit functioning in one or more activities of daily life across multiple environments, such as home, school, work, and community; and (3) onset of intellectual and adaptive deficits during the developmental period (prior to the age of 18). Four levels of ID severity (mild, moderate, severe, and profound) are delineated on the basis of adaptive functioning rather than IQ scores, within three domains (conceptual, social, and practical). Detailed examples/criteria descriptions of the ID severity level by adaptive functioning domain matrix are provided by APA (2013, Table 1, pp. 34–36).
