Distribution of Autism-Associated Behaviors in a General School-Aged Population: Findings from a Population-Based Study in Taiwan

Background: Heterogeneity in the severity of autism-associated traits and behaviors across individuals with autism spectrum disorder (ASD) has led researchers to suggest the disorder forms a continuum that extends into general populations.  Little is known about the distributions of these ASD-associated traits and behaviors in general populations.  If the spectrum of the disorder exists, as many researchers agree, it would be critical to establish a population reference level of the associated traits and behaviors, and to examine the distribution of the disorder’s severity in a general population.  The Social Communication Questionnaire (SCQ) is a widely used screening tool for ASD, with established reliabilities and validities from samples with higher risk of ASD.  However, to our knowledge, there is no report on how SCQ-measured traits and behaviors are distributed in the general population.

Objectives: To obtain a population reference of SCQ measured ASD-associated traits and behaviors; and to examine distributions of these measured behaviors by gender in a large population of school age children.

Methods: A population-based epidemiologic study of autism in children aged 6-8 years involving a multi-stage case identification design was conducted in PingTung, Taiwan from 2008-2010.  The SCQ was used as a screener to identify children at high risk for ASD.  On the SCQ, 36 of 40 items have been classified into 3 domains: social interaction, communication, and restricted/repetitive/stereotyped behaviors (RRB).  Studies from Western countries recommend a cut-point of 15 on the SCQ for differentiating between likely ASD and non-ASD diagnoses.  Rather than only administer the SCQ on children with higher risk of ASD, for this study it was administered on all children who attended any of 130 schools in the study catchment area.  This analysis includes a total of 2279 primary caregivers (60.0% mothers, 17.5% fathers, 22.5% grandparents and others) who completed the screener on their child (1083 boys and 1156 girls). 

Results: Overall, the prevalence of SCQ measured traits/behaviors vary in this school aged population, ranging from 3.8% (cannot have a to-and-fro conversation) to 34.1% (no use of gestures).  Boys and girls have similar patterns of item score distributions; however, RRB item scores are significantly higher in boys.  Very similar proportions of boys and girls have SCQ>=15 (9.14% for boys, 9.08% for girls).

Conclusions: Boys are not at higher risk than girls of meeting the SCQ clinical cutoff (>=15) in this defined population.  In other words, our results do not support the observations that more boys than girls are meeting ASD clinical thresholds.  While the majority of reports on SCQ are from higher risk populations, this study uniquely demonstrates the distribution of SCQ measured behaviors in a “general population”.  While the global autism research community has made every effort to find causes of ASD, it is necessary to examine the extent to which ASD-associated traits and behaviors are distributed in general populations.  Such understanding may help shed light on finding etiologic factors of the disorder.