However,studies using experimental measures en-compassing both higher- and lower-level repetitive be-haviour (i.e. algorithm and non-algorithm items of the Autism Diagnostic Interview-Revised and the Infant Be-havioral Summarised Evaluation) have found a range of repetitive behaviours (both higher- and lower-level) to differentiate children with autism who are older than 3 years,taking developmental level into account [1,17,18]. These findings suggest that repetitive behaviour is a re-liable diagnostic feature of autism in children older than 3 years.
Evidence that the expression ofrepetitive behaviours may occur as a function of developmental progression is reported by Cox etal.[6].Comparisons were made at 20 and 42 months of age between 8 children with autism,13 with other PDDs,9 with language delay and 15 who were developing normally. Although repetitive behaviours did not significantly distinguish subjects with autism from the other groups at either 20 or 42 months,more subjects with autism or other PDDs were displaying repetitive behaviours at 42 months ofage.These behav-iours included hand,finger,and complex body manner-isms and repetitive use of objects.
The current study examined whether repetitive be-haviours are a feature of autism in children aged less than 51 months,independent of developmental level,by investigating the relationship between chronological age, developmental age and the presence of repetitivebehaviours. These questions were also addressed in re-lation to Turner’s definition of higher-level and lower-level repetitive behaviours [34].