utism is about 10 times as prevalent today as it was
in the 1980's, according to the country's largest study ever
on the problem. Some of the increase is the result of widened
definitions of the disorder, researchers say, but the
explanation for the rest of the increase is unknown.
The study, conducted in metropolitan Atlanta in 1996, found
that 3.4 in every 1,000 children ages 3 to 10 had mild to
severe autism that year. In the late 1980's, 4 to 5 in every
10,000 children were thought to be afflicted.
The higher rate, described in today's issue of the Journal
of the American Medical Association, is in line with rates
found in recent smaller studies in the United States and
abroad in which the autism prevalence was 4 to 6 children in
The researchers, from the federal Centers for Disease
Control and Prevention, said the prevalence rates they found
would mean that at least 425,000 Americans under age 18 have
some form of autism.
Dr. Marshalyn Yeargin-Allsop, an epidemiologist at the
National Center on Birth Defects and Developmental
Disabilities, led the study.
Some of the increase can be explained by changes in the
definition of autism, a brain disorder in which normal social
interaction is difficult or impossible. The definition has
widened to include milder forms.
Many experts believe that autism results from an interplay
of genes and unknown environmental factors.
Dr. Yeargin-Allsop said the researchers canvassed schools,
clinics, doctors, nonprofit programs and other places that
autistic children might have gone for services in 1996.
Studies that look at autistic children in just one setting,
like special clinics, tend to find lower rates, she said.
Experts reviewed the medical records of each child and
determined whether autism was diagnosed accurately. They did
not examine the children themselves. Out of the 289,456
children ages 3 to 10 living in the metropolitan Atlanta in
1996, 987 had mild to severe autism.
Dr. Yeargin-Allsop said 18 percent of the children found to
have autism in 1996 had never had an accurate diagnosis. Many
had been classified as having general developmental
difficulties; the higher-functioning children had been missed
The Atlanta study found that rates were the same for blacks
and whites but confirmed studies finding that autism is four
times more common in boys than in girls.
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