Behavioral scientists from the CDC's National Center on Birth Defects and Developmental Disabilities have determined that autism spectrum disorders may be more common than previously thought.

Nationwide surveillance program had been conducted at sites in 14 states in 2002 and it showed that the overall prevalence of ASD was around 6.6 per 1,000 eight-year-old children, ranging from a low of 3.3 per 1,000 in Alabama to a high of 10.6 per 1,000 in New Jersey.

Researchers report that even if the lowest prevalence estimates were the actual prevalence rates, they would still be considerably higher than previously thought. The previous numbers ranged between four to five per 10,000 and two to three per 1,000.

Putting these estimates into exact numbers, approximately 560,000 children from the ages of birth to 21 years may be living with an autism spectrum disorder.
These numbers cannot be used to describe a nation pictures but only the picture of areas studied. Wider studies are needed to see if there’s an upward trend in autism spectrum disorders.

It is also not known if there’s actual increase in the ASD prevalence or the increase is the result of better studies and diagnosing tools.
Autism spectrum disorders is a category that includes autistic disorder, pervasive developmental disorder, not otherwise specified (PDD-NOS), and Asperger's syndrome.

The researchers looked at data on eight-year olds who were identified as having an autism spectrum disorders because that is the age by which nearly all cases of autism spectrum disorders would be detected by this age. The median age of earliest autism spectrum disorders diagnosis ranged from four years, four months in New Jersey and West Virginia to four years, eight months (Georgia). But, for 69% to 88% of children with an autism spectrum disorders, parents or caregivers had recorded concerns about the child's development age three.

Scientists reported that it is essential they continued to monitor prevalence of autism spectrum disorders and to improve the understanding of these disorders. Better knowledge of the ASD prevalence should aid in school and health officials planning and intervention efforts.

Like already mentioned, the difference in autism spectrum disorders prevalence between current and earlier estimates are still unknown and will stay unknown until further research is done.