Prevalence of autism in a US metropolitan area.

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http://www.ourstolenfuture.org/NewScience/behavior/2003/2003-0101yeargin-allsopp\

etal.htm

 

 

Yeargin-Allsopp, M, C Rice, T Karapurkar, N Doernberg, C Boyle and C Murphy.

2003. Prevalence of autism in a US metropolitan area. Journal of the American

Medical Association 289:49-55.

 

 

 

Press coverage:

Atlanta Constitution Journal

New York Times

Reuters Health

 

Recent surveys of autism in Brick Township, NJ, California and Britain had

surprised experts because the numbers were so large, running up to ten times

higher than historical rates would indicate. This new report from the US Centers

for Disease Control finds that the number of autistic children living in the

Atlanta region is also high, 3.4 per thousand, consistent with the more recent

surveys. Most of the autistic children were boys.

 

This rate does not indicate that Atlanta's rate is higher than other regions in

the US. Too few current data are available to reach that conclusion. More

likely, other regions in the US are experiencing these higher rates also, at

least judging from reports of increased demand for special education services

for autistic children.

 

This survey, the largest of its kind ever undertaken in the US, was unable to

resolve a key question: how much of the increase is a real change in the

frequency of autism vs. artifactual changes that might result from changes in

diagnosis definition, surveillance method or parental incentives to report

cases? It nonetheless serves as an important, perhaps definitive benchmark

against which to compare future research. It also yielded important insights

into the demographics of autism, particularly on risks for boys vs. girls and on

race.

 

The CDC has studies underway in other 13 other communities around the US

designed to provide better information.

 

What did they do? Yeargin-Allsopp et al. mounted an ambitious 5-county survey in

the Atlant area to identify all children with any form of autism between the

ages of 3 and 10. Their work was carried out in two phases.

 

First, they systematically reviewed as many relevant medical/educational (at

many different medical, clinical and educational institutions) to identify all

children who had been screened using methods that would allow them to be

classified as autistic.

Second, a team of experts scoured through these records and independently

determined whether the children met the criteria for autism. They included three

variants of autism (collectively referred to as autism spectrum disorder):

autistic disorder ( " classic autism), Asperger disorder, and pervasive

developmental disorder-not otherwise specified " (PDD-NOS). Their diagnoses

followed the criteria described in the standard " Diagnostic and Statistical

Manual of Mental Disorders, 4th Edition. " This detail is important because it a

somewhat broader set of criteria than used in previous decades.

 

Note also that this survey was all through analysis of records; no children were

seen directly.

 

What did they find? Of the 289,456 children aged 3 - 10 living in the 5-county

metropolitan Atlanta area in 1996, 987 were found to meet the criteria for

autism spectrum disorder. This rate is 3.4 per 1000.

 

No differences were found between children of different races. Most of this

children surveyed were either black (38%) or white (58%).

 

Overall, boys were more likely to be autistic than girls: 5.3 vs. 1.5 per 1000,

respectively.

 

This ratio did not prevail across all degrees of autism, however. As can be seen

to the right, the sex ratio decreased with severity of impairment of cognitive

function. The number without impairment was much greater than those with severe

impairment.

 

 

 

 

This graph is based upon the number of children in the sample with tests of

cognitive ability available for review. N for children with no cognitive

impairment was 280; for those with an IQ score less than 20, N = 23.

 

 

This pattern is consistent with prior studies.

 

 

 

Yeargin-Allsop et al. also found that the rate of autism varied with age (left).

They note that it is not surprising to observe lower rates at the youngest ages,

because the syndrome either may not have developed or been diagnosed. The

decline at ages 9 and 10 raises other questions, perhaps having to do with

changes in diagnostic criteria. Narrower criteria were used before the

publication (1994) of those used in this study.

 

 

 

What does it mean? This research serves best to provide a rigorous benchmark for

the prevalence of autism in a large metropolitan area, Atlanta, within the US.

Rates in Atlanta are consistent with other recent studies, and differ from those

in previous decades.

 

Unfortunately, because of changes in diagnostic procedures, in public attention

given to autism, and in the nature of services provided to autistic children

(altering incentives for reporting), " debate continues about whether the overall

prevalence of autism has increased or whether past rates underestimated true

prevalence. "

 

Recent work conducted for the California State Legislature presented several

analysis supporting the interpretation that the change is real. This work is

available publicly, but has not yet been peer-reviewed. That review process may

reveal weaknesses in the conclusions not readily apparent.

 

The authors of the current study conclude that this debate " is difficult to

conclude retrospectively.

 

 

 

 

 

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