Longitudinal Profiles of Adaptive Behavior In Children with ASD From Ages 2 to 8

Background:

Research has shown a widening gap between IQ & adaptive behavior across age groups in ASD, with older individuals having poorer functional skills comparative to younger individuals. This is particularly evident in higher functioning ASD, with discrepancies emerging as early as age 4. However, most studies to date have been cross-sectional and have not included a broad IQ range. Less information is known about the relationship between cognitive and adaptive skills within the same group of individuals over time, and the role that level of IQ plays.

Objectives:

The relationship between IQ and adaptive functioning, measured by the Vineland, is investigated in a longitudinal sample of children at ages 2, 4, and 8. Acquisition of cognitive and adaptive skills over time and the gap between these constructs are examined.

Methods:

Participants included 46 children with ASD with mean ages of 28 months at Time 1, 53 months at Time 2, and 104 months at Time 3. The sample included 24% females and 76% males.

Results:

Mean IQ scores (SDs) for the 3 age groups using ratio IQ scores for the Mullen Scales of Early Learning and General Conceptual Ability scores for the Differential Ability Scales, Second Edition were as follows: Age 2: 68.10 (17.19); Age 4: 86.49 (22.56); Age 8: 88.68 (25.17). A Repeated Measures ANOVA revealed that cognitive skills significantly improved from ages 2 to 4 and 2 to 8, but remained stable between ages 4 and 8 (F=37.80, P<.001). Mean Vineland Adaptive Behavior Composite scores, Expanded Form, were as follows: Age 2: 74.07 (10.88); Age 4: 67.43 (11.24); Age 8: 77.09 (16.89), with significant improvements noted between ages 4 and 8 (F=3.84, p=.064). Significant discrepancies were evidenced between mean IQ and Vineland scores at Age 4 (t=-7.56, p<.001) and Age 8 (t=-5.96, p<.001), but not at Age 2 (t=.25, p=.81). The gap between IQ and adaptive skills significantly widened from ages 2 to 4 and 2 to 8, but remained stable from 4 to 8 (F=18.96, p<.001), with Vineland scores falling significantly below IQ at ages 4 and 8. Profiles differed between individuals with high (>70) vs. low (<70) IQ, with adaptive daily living skills being the most impaired area of adaptive functioning in the High IQ group, yet the strongest adaptive area in the Low IQ group. In general, adaptive skills were higher than cognitive skills in the Low IQ group, and lower than cognitive skills in the High IQ group.

Conclusions:

Results indicate that despite acquiring cognitive and adaptive skills overtime, children with ASD evidence significant deficits in adaptive functioning as early as age 4 that continue through age 8. Consistent with previous findings, profiles of adaptive functioning greatly differ between individuals with low vs. high IQs, with overall adaptive functioning being stronger than cognitive ability in the less cognitively able group, and significantly lower than IQ in the more cognitively able group. Given the strong role of adaptive functioning in adult outcome, predictors of adaptive functioning are examined and implications for intervention are discussed.