01:00 AM EDT on Friday, September 30, 2005

I HAVE a guilty pleasure that I feel the need to confess: I listen to Imus in the Morning on the radio as I drive to work every day. The guilt stems from my inability to reconcile my image of myself as a mature, thoughtful child psychiatrist with Imus's self-absorbed, insulting, misanthropic, chauvinistic, patronizing, ranting radio persona.

The pleasure, which far outweighs the guilt, is derived from his willingness to say anything, his adolescent humor, and his endless series of irreverent interviews with politicians of every hue.

I am also fascinated by the influence he seems to wield -- the reason, no doubt, that so many public figures tolerate his questions and his abuse.

Of late, however, I've been cringing at the recognition that Imus's influence is being applied to counterbalance the best scientific understanding we have of autism. Imus and an increasing number of Americans seem convinced that a) there is an autism epidemic and b) it is caused by childhood immunizations.

My best reading of the available evidence suggests that neither is true.

It is a fact that more children than ever are being diagnosed as autistic. On the face of it, that fact is grounds for concern about an autism epidemic.

However, much of the change in prevalence has to do with the broadening of the definition of autism. When the categorization of autistic-spectrum disorders was improved and expanded, the numbers were sure to rise, even if nothing else changed.

In addition, the stigma associated with all psychiatric disorders has been decreasing. And thanks to the advocacy of parents, autism has progressed especially far toward destigmatization. So professionals are asked about it more often, training programs provide better education on how to recognize and treat autism, and school systems screen for it more frequently.

The bottom line is that there is more evidence for better recognition of previously missed cases than for an actual increase in the number of autistic children in the United States.

A recent study by Eric Fombonne and colleagues, published in June in The American Journal of Psychiatry, looked at the question in an important way: They redid a careful epidemiologic study of a large population of children in Stafford, England. The initial study, of 16,000 children born between 1992 and 1995, was repeated on 11,000 children in the same location born between 1996 and 1998. The two studies employed the same rigorous, exhaustive methods to evaluate the same diagnostic criteria. Overall, the prevalence rate of pervasive developmental disorders was 63 per 10,000 children in the first study and 59 per 10,000 in the second (the apparent decrease was not statistically significant). Further, there were no significant differences between subtypes of pervasive developmental disorders (autism, Asperger's disorder, PDD-NOS, etc.).

Imus is publicizing the view that mercury in thimerosal, a preservative used in vaccines, is causing the purported autism epidemic. To accept this proposal, one must discount a number of studies that have diligently sought to prove the connection: None has found a theoretical, clinical, or epidemiologic link.

One must also believe that the Institute of Medicine, the Centers for Disease Control and Prevention, and the American Academy of Pediatrics, in their review of the data, are orchestrating a coverup to protect the companies that make vaccines. I find this incredible, but for many people, Imus's dogmatism is more convincing than scientific evidence.

Chelation therapy for autism is now a cottage industry, and at least one child has died in the course of such treatment. In addition, some parents question the wisdom of immunizing their children because of "the risk of autism" -- even though thimerosal is now almost totally gone from vaccines.

That one's child has an autism-spectrum disorder is usually heartbreaking news, and the impact on family life can be devastating. And though we mental-health professionals work hard to provide important treatment and lots of coping advice, we don't know the cause of autism, so we can't yet cure it.

Thus, it's no surprise that desperate parents -- supported by the good intentions and passion of social icons such as Imus -- embrace unproven but "hopeful" advances. It is human nature to want to replace the unknown with understanding, and when science lacks the answers, people turn to forcefully voiced opinions. In Imus's case, it's also good for ratings.

Gregory K. Fritz, M.D., an occasional contributor, is editor of The Brown University Child and Adolescent Behavior Letter, a Brown professor of psychiatry, medical director of Bradley Hospital, and director of child and family psychiatry at Hasbro Children's Hospital.