Measurement of nonverbal IQ in autism spectrum disorder: scores in young adulthood compared to early childhood.

Nonverbal IQ (NVIQ) was examined in 84 individuals with autism spectrum disorder (ASD) followed from age 2 to 19. Most adults who scored in the range of intellectual disability also received scores below 70 as children, and the majority of adults with scores in the average range had scored in this range by age 3. However, within the lower ranges of ability, actual scores declined from age 2 to 19, likely due in part to limitations of appropriate tests. Use of Vineland-II daily living skills scores in place of NVIQ did not statistically improve the correspondence between age 2 and age 19 scores. Clinicians and researchers should use caution when making comparisons based on exact scores or specific ability ranges within or across individuals with ASD of different ages.