Collecting the data took five years. Researchers had the parents or teachers of children, gathered from the rolls of regular and special education schools and a disability registry, answer an autism spectrum screening questionnaire. Children who screened positive for possible autism were offered more comprehensive assessments.
They found that 2.6 percent of the children had an autism spectrum disorder. Among children in special education with an autism spectrum disorder, boys outnumbered girls five to one. In the general population, the ratio was 2.5 to one, the study found.
The reason for the differences, according to the researchers, may be that children who are receiving special services are more likely to have intellectual disability, and intellectual disability is more common among males than females.
In the special education group, about three-fourths of the children had classic autism and one-fourth had a milder form, such as Asperger's syndrome or Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS).
In the other children, three-fourths had PDD-NOS or Asperger's, and one-fourth had classic autism.
The average IQ of children in the general population suspected to have autism was higher than it was for children in the special education group (98 vs. 75). About 59 percent of children with autism in the special education group had an intellectual disability, but just 16 percent of those with autism in the general school population did, and even then it tended to be mild.
Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at the Steven and Alexandra Cohen Children's Medical Center of New York
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