Apr 06 2011
I have been following the literature on autism diagnosis both because of my general interest as a neurologist, but also because it is at the center of the vaccine-autism myth. There is no question that autism diagnoses have been on the increase over the last 20 years. There are some who assume that this increase in the number of diagnoses being made represents a true increase in the incidence of the disorder – hence an autism “epidemic”.
However, careful analysis reveals that the increase in diagnosis is largely explained (perhaps completely explained – but a small real increase cannot be ruled out) by increased awareness of autism and an expanded diagnosis. (See my earlier posts for a full explanation.)
A recent study sheds further light on this issue. The study was not addressing the broader question of the causes of the increase in autism diagnosis, but rather was focusing on socioeconomic disparities in diagnosis. The results, however, do lend support to the conclusion that the rising autism diagnoses was largely due to increased awareness, rather than a true increase.
Peter Bearman and others were looking for trends in the California system for autism diagnosis between 1992 and 2000. What they found is that autism diagnoses increased disproportionately in wealthier families, but more significantly in wealthier neighborhoods.
“At the height of rising prevalence, which involved children born between 1992 and 1995, kids whose parents had fewer economic resources simply weren’t diagnosed as often as wealthier children— wealthier kids were 20 to 40% more likely than poorer children to be diagnosed,” said study coauthor Marissa D. King, an assistant professor of Organizational Behavior at Yale University’s School of Management “Among children born in 2000, however, parental wealth alone had no effect on the likelihood that a child would be diagnosed.”
Even though the effect of wealth alone disappeared over time, the neighborhood effect remained strong:
According to the study, on average among children born between 1992 and 2000, a child from a poor family that lived in a more affluent neighborhood was close to 250% more likely than a child from an equally disadvantaged family living in a poorer neighborhood to be diagnosed with autism.
This supports other research that shows that the risk of getting an autism diagnosis increases with access to other families with a child with the diagnosis, but not necessarily physical closeness. The researchers conclude from all this that parents talking to parents is the significant variable increasing the probability of getting a diagnosis – parents telling other parents what to look for, and how to navigate the service system. Wealthier neighborhoods have more of an infrastructure and more opportunity for this interaction.
In addition, as further support, Bearman found that wealthier families had a higher proportion of autism diagnoses considered to be at the subtler end of the spectrum – indicating a greater sensitivity in screening for and making the diagnosis.
The totality of this research supports the conclusion that the increase in autism diagnoses during this time was largely driven by diagnostic practices – knowledge of the diagnosis, the availability of services, and parents discussing the diagnosis and how it relates to obtaining services.
In short – we see a sociological pattern of increase in the autism diagnosis over this time, not a biological pattern.
Reference: Socioeconomic Status and the Increased Prevalence of Autism in California.
Marissa D. Kinga and Peter S. Bearman
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