title: Investigating the structure of the restricted, repetitive behaviours and interests domain of autism.
abstract: BACKGROUND
  The Restricted, Repetitive Behaviours and Interests (RRBIs) are represented in the DSM-IV and measured by the Autism Diagnostic Interview-Revised (ADI-R) as one of the three homogeneous symptom categories of Pervasive Developmental Disorders. Although this conceptualisation is well accepted in the field, the grouping of symptoms is based primarily on clinical judgment rather than on empirical evidence.
  
  
  METHODS
  The objective of this study was to examine the factor structure of the RRBI domain of autism. Eleven items from this domain of the ADI-R were used in a Principal Components Analysis (PCA). Our sample consisted of 339 individuals with a Best Estimate diagnosis of Pervasive Developmental Disorder (PDD).
  
  
  RESULTS
  Findings indicate that the RRBI domain is composed of two distinct factors or dimensions: Insistence on Sameness (IS) and Repetitive Sensory and Motor Behaviours (RSMB). RSMB is negatively correlated with adaptive skills; that is, lower functioning individuals tend to have higher levels of repetitive sensory and motor behaviours. On the other hand, IS is positively correlated with autistic symptoms in the communication and language domain. Further analyses suggest moderate familial aggregation among affected sibling pairs within the IS but not the RSMB factor.
  
  
  CONCLUSIONS
  These results provide evidence for the heterogeneity of the RRBI domain of the ADI-R in terms of both clinical presentation and other correlates. In addition, the IS factor seems to be under familial (presumably genetic) control, while RSMB appears to simply reflect variation in developmental level.
authors.affiliation: Department of Psychiatry and Behavioural Neurosciences, McMaster University, Canada. szatmar@mcmaster.ca
authors.forename: Peter
authors.initials: P
authors.lastname: Szatmari
authors.forename: Stelios
authors.initials: S
authors.lastname: Georgiades
authors.forename: Susan
authors.initials: S
authors.lastname: Bryson
authors.forename: Lonnie
authors.initials: L
authors.lastname: Zwaigenbaum
authors.forename: Wendy
authors.initials: W
authors.lastname: Roberts
authors.forename: William
authors.initials: W
authors.lastname: Mahoney
authors.forename: Jeremy
authors.initials: J
authors.lastname: Goldberg
authors.forename: Lawrence
authors.initials: L
authors.lastname: Tuff
mesh_terms: D000223:Adaptation, Psychological; D000293:Adolescent; D001321:Autistic Disorder / Q000453:epidemiology*; D002648:Child; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D010507:Periodicity; D015995:Prevalence; D011596:Psychomotor Disorders / Q000453:epidemiology*; D012720:Severity of Illness Index; D019956:Stereotypic Movement Disorder / Q000453:epidemiology*