In brief

Is the rate of autism rising?

If you consider only certain statistics, you might conclude that children in advanced industrial societies are suffering from an epidemic of autism. Figures published by the U.S. Department of Education and based on the number of children receiving special education show an exponential rise in the number of cases during the 1990s. But a critical study published in the journal Pediatrics shows that these numbers are unreliable, and a careful English survey confirms that children born in 1998 are no more likely to develop autistic disorders than those born in 1992.

The American data, collected under the Individuals with Disa­bilities Education Act and presented annually to Congress, indicate that there were 4 cases of autism per 10,000 children in 1993 and 25 cases per 10,000 in 2003 — a sixfold increase. But these findings contain internal inconsistencies. Apparently, as many children are being newly diagnosed at age 15 as at age 8, yet the symptoms of autism appear before age 3, and most studies show that the diagnosis is usually made before age 8. Oddly, the government's figures also show a drop in reports of new cases between ages 11 and 12, just when an increase might be expected because children are making the difficult transition from elementary to middle school.