Stelios Georgiades1, Eric Duku1, Isabel Smith2, Pat Mirenda3, Peter Szatmari1, Susan Bryson2, Eric Fombonne4, Wendy Roberts5, Tracy Vaillancourt1, Joanne Volden6, Charlotte Waddell7, Lonnie Zwaigenbaum8, and Pathways in ASD Study Team. (1) Offord Centre for Child Studies & McMaster University, Hamilton, ON L8N 3Z5, Canada, (2) IWK Health Centre, Dalhousie University, (3) University of British Columbia, (4) Montreal Children's Hospital & McGill University, (5) The Hospital for Sick Children & University of Toronto, (6) University of Alberta, (7) Simon Fraser University, (8) Glenrose Rehabilitation Hospital & University of Alberta
Background: The Repetitive Behavior Scale-Revised (RBS-R; Bodfish et al., 2000) was designed to examine restricted/repetitive behaviors in ASD. A recent factor analytic study by Lam and Aman (2007), using a sample of older children and adults (mean CA=184 months), revealed five factors. Objectives: To examine the factor structure and correlates of the RBS-R in preschool children with ASD. Methods: The RBS-R was completed by parents of newly-diagnosed children with ASD, participating in a Canadian longitudinal study (Pathways in ASD). Our sample consisted of 225 children (193 males; mean CA=39.80 months; mean MA=26.00 months; 69.8% Caucasian). Principal axis factor analysis was used to examine the structure of the RBS-R. Pearson correlations were calculated to examine relationships between derived factors and other ASD symptoms, as well as cognitive and adaptive function. Results: A three-factor solution explaining 40.2% of the variance was selected, using scree plot and goodness-of-fit criteria. The three factors were: Compulsive Ritualistic Sameness Behaviour (CRSB), Self Injurious Behaviour (SIB), and Stereotyped Restricted Behaviour (SRB). Children with higher CRSB scores were significantly older (r=.22), showed more severe autism symptoms (SRS and ADI-R, r=.15 to .58), and had poorer adaptive behavior (Vineland II, r=-.29). High scores on SIB were associated with higher SRS scores (r=.21). Children with high scores on SRB were younger (r=-.15), had more severe autism (ADI-R, ADOS & SRS, r=.11 to .23), and were more impaired on both cognitive (M-P-R) and adaptive (Vineland II) skills (r=-.17 to -.33). Males scored higher on the SRB factor (p<.01). Conclusions: The structure of the RBS-R is best captured using fewer, more inclusive factors in a population of preschool children, compared with a previous factor analysis in an older sample. This ongoing longitudinal study may reveal useful information on increasing differentiation of repetitive behaviours, as well as potential factors associated with their development.