Intellectual disability (ID)

Intellectual disability is characterized by significant limitations both in intellectual functioning (reasoning, learning, problem solving) and in adaptive behavior, which covers a range of everyday social and practical skills. This disability originates before the age of 18.

ID affects between 3% and 5% of the general population

ID can not be determined by just an IQ test. The evaluation and classification of ID is a complex issue. There are three major criteria for intellectual disability: significant limitations in intellectual functioning, significant limitations in adaptive behavior, and onset before the age of 18. The IQ test is a major tool in measuring intellectual functioning, which is the mental capacity for learning, reasoning, problem solving, and so on. A test score below or around 70—or as high as 75—indicates a limitation in intellectual functioning. Other tests determine limitations in adaptive behavior (Conceptual skills, social skills, practical skills).

ID co-existing with other neurodevelopmental conditions

Current estimates suggest that 40% of people with autism have mild and 15% severe ID, and that there is also clinical overlap between ADHD and ID.