Objectives: The present research aims to examine whether number of siblings is associated with ToM performance in children with ASD.
Methods: Participants were 24 children with ASD from a larger national study. Parents were mostly Caucasian, middle-class, and well-educated. ASD diagnoses were made when the national study was initiated. At about age nine, children were administered a battery of four ToM tasks: verbal and non-verbal appearance-reality tasks and two first-order false-belief tasks. Each task was administered twice, separated by approximately two weeks. For each set of ToM tasks, a score of zero was assigned for not passing both assessments, a score of one for passing one of the assessments, and a score of two for passing both assessments. Scores were obtained for each task and a composite score was calculated. Sibling information was gathered by telephone or mail and was coded as no siblings, one sibling, or two or more siblings.
Results: ANCOVA was used to determine whether children with two or more siblings performed differently from those with one sibling, with receptive language ability (PPVT) serving as a covariate. Results indicated that children who had more than two siblings performed better on the verbal appearance-reality tasks (M = 1.09, SE = .22) relative to children who had one sibling (M = 0.46, SE = .22; F(1, 22) = 4.40, p = .05); the remaining task scores and the composite score did not differ between groups. All analyses were also conducted with child age serving as a covariate and the results were comparable.
Conclusions: The findings suggest that a greater number of siblings may facilitate performance on some aspects of ToM, particularly the appearance-reality distinction. Results support research that posits social benefits for children with siblings (McAlister & Peterson, 2006). This work contributes to the literature on cognitive differences in children with ASD by indicating that variability in ToM performance exists in relation to the family context. It is believed that sibling interaction provides a more developmentally appropriate model for an emerging ToM than that provided by adult interaction. These findings bear importance for the development of appropriate intervention strategies for children with ASD.