A basic tenet of America’s ill-conceived and foundering anti-vaccine movement holds that autism diagnoses have risen to epidemic proportions. Among the faithful, this imagined increase is “the initial fork in the road in the autism debate,” one that colors their entire understanding of autism. But is the increase real, or an artifact of how autism spectrum disorders are diagnosed and counted?
New data from California indicate the latter. The number of special education students with autism in the Golden State has more than tripled since 2002 , as the rate rose form 2.6 to 8.8 percent, but the overall special education enrollment has remained nearly unchanged, according to an analysis of state education data.
More than 680,000 students – 11 percent of all California public school students – are enrolled in special education. The number of students diagnosed with autism climbed from 17,508 in 2002 to 59,690 in 2010, the Lucile Packard Foundation for Children’s Health found.
Meanwhile, the rate of learning disability diagnoses fell in the eight year period, from 52.4 to 42.3 percent. Speech or language impairment affects about one-quarter of special education students in California.
Making sense of the claims for an autism epidemic is essential for any critical evaluation of anti-vaccine claims. A good first step is learning the difference between prevalence and incidence. Dr. James Coplan, a development pediatrician writing in Psychology Today, compares prevalence and incidence to the gas gauge and speedometer on your car.
Prevalence is a percent: either the percent of your tank that contains gas, or the percent of children with ASD. The prevalence of an ASD diagnosis among children has certainly risen in the past decade (although even the claim of an “explosion” of persons with ASD – as opposed to persons with a diagnosis of ASD – turns out to be bogus – we’ll get to that a few posts down the road).
Incidence is a rate: either your speed in miles per hour, or, in the case of ASD, the rate at which new cases of ASD are occurring. An epidemic is defined as a sudden increase in incidence. There is simply no evidence to support the claim that there has been a change in incidence. And until someone figures out how to stand in the delivery room and count autistic-to-be babies as they are born, we are not likely to have such evidence.
Anti-vaccine activists mislead parents and journalists when they ignore these differences. Jenny McCarthy’s Generation Rescue, arguably the best funded and most influential anti-vaccine interest group in the US, placed a full page ad in USA Today two years ago which claimed that the “autism rate” has risen from 1:10,000 to 1:150 between 1983 and 2008. The ad compared the purported rise in diagnoses to an increase in the number of diseases that children are now protected against, compared to 25 years earlier, to imply causality. “How awesome that Jenny Mccarthy (sic) and Jim Carrey and Generation Rescue have placed this ad to let everyone know what those of us in the Autism community have known for a while now…..that autism IS caused by vaccinations,” is how one vaccine rejectionist expressed the centrality of the epidemic myth to the anti-vaccine movement.
Journalists and columnists are still taking the bait. In his recent column titled Autism epidemic linked to red herring consumption, Bob Herrara at NorthJersey.com wrote:
Have you heard the news? They finally found a cause for the skyrocketing rate of autism in children!
The reason so many kids are being diagnosed with autism today is…
No, you haven’t heard that news. It hasn’t happened yet.
Even though I, along with millions of other parents of autistic children, have waited years for modern science to explain why autism rates have climbed from 1-in-10,000 children two decades ago to 1-in-100 kids today, there is still no answer.
The 1:10,000 rate has no real basis in fact. The earliest autism epidemiological study was by Lotter in 1966, who found 4.5:10,000 children with Kanner’s autism, defined as “a profound lack of affective contact with repetitive, ritualistic behaviour, which must be of an elaborate kind.” But Herrara and other Generation Rescue stenographers still repeat the 1:10,000 figure.
Parents and journalists aren’t the only ones falling for McCarthy’s fuzzy math.
“Autism is an epidemic that we can no longer ignore,” intoned Virginia State Delegate Tag Greason, R-Loudoun County, who sponsored a bill to mandate insurance coverage for childhood autism. While supporting families with autism is a worthwhile endeavor, there is nothing productive about misleading lawmakers and the public about autism spectrum disorders.
Congressman Dan Burton, (R-Indiana), whose anti-vaccine jihad goes back a decade, recently invoked the apocryphal 1:10,000 rate a letter to the CDC :
About 20 years ago, autism was considered a rare disease, affecting about 1 in 10,000 children. Now, that rate is about 1 in 150; making
autism more common than pediatric cancer, diabetes, and AIDS combined.
Twenty-years ago? Not according to Christopher Gillberg, et. al. who tracked autism prevalence in Goteborg, Sweden in the 1980s. They concluded:
A total population study of children, aged 13 years and under, suggested that there has been an apparent rise in the frequency of autistic disorder and autistic-like conditions (excluding Asperger’s syndrome) in one area of western Sweden over the last ten years. The frequency was 4.0/100,000 in 1980, 7.5/10,000 in 1984 and 11.6/10,000 in 1988 in the city of Goteborg. Even though the prevalence rates refer to slightly different age cohorts, it was concluded that the apparent increase is in part due to better detection, but also to new cases born to immigrant parents.”
Gillberg worked from far more restrictive criteria than what is found in latest Diagnostic and Statistic Manual, and still found a rate 11 times greater than what is claimed by Burton.
None of this is to say that the evidence against an autism epidemic is overwhelming, only that there are no good data pointing to an increase in incidence, and the increase in prevalence has more rational explanations that what Jenny McCarthy’s Generation Rescue promotes. “The evidence suggests that the majority, if not all, of the reported rise in incidence and prevalence is due to changes in diagnostic criteria and increasing awareness and recognition of autistic spectrum disorders,” Dr. Lorna Wing, another pioneer in autism epidemiology, wrote in 2002. “Whether there is also a genuine rise in incidence remains an open question.”