According to widely publicized estimates, one in 68 is now the proportion of children who suffer from autism. This proportion is astonishingly high compared with the figure of one in 2,500 that autism researchers had accepted for decades. Across a mere 10-year period–1993 to 2003–statistics from the U.S. Department of Education revealed a 657% increase in the nationwide rate of autism.

Not surprisingly, these bewildering increases have led many researchers and educators to refer to an autism epidemic. Representative Dan Burton of Indiana also declared in 2001 that we have an epidemic on our hands. But what’s really going on?

Before we explore this question, a bit of background is in order. Autism is a severe disorder that first appears in infancy. Individuals with autism are characterized by problems with language, social bonding and imagination. All suffer from serious communication deficits, and some are mute. They do not establish close relationships with others, preferring to remain in their own mental world.

Read:African-American Children Receive Diagnosis of Autism Later Than Others

They engage in highly stereotyped and repetitive activities, exhibiting a marked aversion to change. About two thirds of autistic individuals are mentally retarded. For reasons that are unknown, most are male.

The causes of autism remain enigmatic, although studies of twins suggest that genetic factors play a prominent role. Still, genetic influences alone cannot account for such a rapid and astronomical rise in a disorder’s prevalence over a matter of just a few years. As a consequence, investigators have turned to environmental factors for potential explanations. The causal agents proposed include antibiotics, viruses, allergies, and enhanced opportunities for parents with mild autistic traits to meet and mate, and, in one recent study conducted by Cornell University researchers, elevated rates of television viewing in infants. Few of these explanations have been investigated systematically, and all remain speculative.

Are Vaccines the Problem?

Yet one environmental culprit has received the lion’s share of attention: vaccines. Indeed, many parents claim that their children developed autism shortly after receiving inoculations, either following a vaccine series for mumps, measles and rubella (German measles)–the so-called MMR vaccine–or following vaccines containing thimerosal, a preservative that contains mercury.

Much of the hype surrounding a link between vaccines and autism was fueled by a widely covered 1998 investigation but since then, 10 of the 13 reports authors have published a retraction of the article’s concussions.

Changing Criteria

An often overlooked alternative explanation for the epidemic: changes in diagnostic practices. Over time the criteria for a diagnosis of autism have loosened, resulting in the labeling of substantially more mildly afflicted individuals as autistic.

Swapped Diagnoses

A 2006 article by University of Wisconsin Madison psychologist Paul Shattuck cited diagnostic substitution: as the rates of the autism diagnosis increased from 1994 to 2003, the rates of diagnoses of mental retardation and learning disabilities decreased. It is possible that the overall pool of children with autism-like features has remained constant but that the specific diagnoses within this pool have switched.

Most experts will agree, it is still too early to exclude the possibility that autism’s prevalence is growing, but it is unlikely that it is growing as swiftly as many have suggested.

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