When my son, who is 19 and was diagnosed at 29 months in 1994, the 'incidence' of reported cases of autism or autism spectrum disorder was something like 4 or 5 cases in 10,000 live births.
More recent figures in the US show the incidence among new birth at something on the order of one in 96 boys and one in 160 girls are diagnosed with some level of disability.
The incidence, alarming as it is, is based on those diagnosed as being in the spectrum of ailments associated with autism and the figures come from both medical and school-based diagnoses that have been confirmed.
The South Korean study went to a typical middle class Korean city and surveyed all the families in the community with a questionnaire asking about behaviors observed by their children. When curious behaviors were seen on the surveys, additional resources were devoted to confirming the behaviors of the individual children by experts.
The result was 2.6 percent of the children in the community between the ages 7 and 12 were diagnosed as being ASD.
The study did find a higher degree of ASD amongst the kids marked for special education but also found a good number in the general population of students.
Among the children with autism spectrum disorder in regular schools, only 16 percent were intellectually disabled, more than two-thirds had a milder form of autism, and the ratio of boys to girls was unusually low: 2.5 to 1.
In addition, 12 percent of these children had a superior I.Q. ó a higher proportion than found in the general population.
The study was funded by the group Autism Speaks.
Notably the CDC section that studies autism admits its record-based approach to determining incidence probably does not capture all the children impacted by ASD as many higher-functioning and more modestly impacted children are never diagnosed; as are many others from lower economic strata. The head of research about autism at the CDC indicated a desire to conduct broader based surveys to get a better understanding.