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The term "high-functioning ASD" is typically used to describe individuals with ASD who have cognitive abilities in the average range. In terms of intelligence quotient (IQ), that usually means greater than or equal to 70 (average IQ is 100, with a standard deviation of 15). Individuals with IQ scores below 70 and daily living skill impairments are usually diagnosed with "intellectual disability" (ID), or what used to be called "mental retardation" (MR).
In light of the DSM-5 removing both Asperger's Syndrome and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS), the term "high-functioning ASD" is sometimes used in place of those previous diagnoses to describe individuals with ASD who have average cognitive skills. The term "high functioning" is often thought to mean average (or above average) functional skills, and low levels of impairment in terms of day-to-day living.
However, recent research suggests that this term might be misleading, and in some cases may disqualify children and teens with ASD from receiving needed services. Spectrum News recently published a story about a large-scale research study on adaptive behavior in individuals with ASD. Adaptive behavior refers to daily living skills that people do independently (e.g., cleaning, showering, putting on clothing, etc). In most individuals without ASD, cognitive abilities (IQ) are highly correlated with adaptive behavior. Essentially, that means most individuals who have higher IQ scores are better at daily living/independent living skills than those with lower IQ scores. This difference in adaptive behaviors is particularly apparent when comparing individuals with and without an intellectual disability. It's not surprising, then, that there is an implicit assumption that individuals with "high functioning ASD" will have adaptive behaviors in the same range as their IQ scores (e.g. in the average range).
The new research study suggests that this assumption is incorrect. In a sample of over 2,000 individuals with ASD, they found that IQ was a weak predictor of adaptive behavior scores. There was a particularly large gap between IQ and adaptive behavior scores for individuals with ASD who had IQ scores over 70 (e.g., those who did not have an intellectual disability; ID). Though there was still a gap between IQ scores and adaptive behavior scores in individuals with ASD and ID, it was a smaller gap than observed for those without ID.