M, C Rice, T Karapurkar, N Doernberg, C Boyle and C Murphy. 2003.
Prevalence of autism in a US metropolitan area.
of the American Medical Association 289:49-55.
surveys of autism in Brick Township, NJ, California
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.
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.
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.
CDC has studies underway in other 13 other communities around the
US designed to provide better information.
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.
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.
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.
also that this survey was all through analysis of records; no children
were seen directly.
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.
differences were found between children of different races. Most
of this children surveyed were either black (38%) or white (58%).
boys were more likely to be autistic than girls:
5.3 vs. 1.5 per 1000, respectively.
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.
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.
pattern is consistent with prior studies.
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.
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.
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."
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.