Definitions: Prevalence & Epidemic
January 16, 2007 by Kristina Chew, PhD
Filed under Health
The Autism Numbers: Why there’s no autism epidemic was the title of Arthur Allen’s review yesterday of Unstrange Minds: Remapping the World of Autism by George Washington University anthropologist Roy Richard Grinker. Allen noted that “thirty years ago, autism was thought to occur in one in 2,000 children; prevalence rates put it at about one in 200.”
To repeat some phrases: “There’s no autism epidemic.” “[P]revalence rates put [autism] at about one in 200.”
I wish to highlight here that “prevalence” and “epidemic” have two quite different meanings.
- Prevalence. “The total number of cases of a disease in a given population at a specific time.”
From the American Heritage Dictionary - Epidemic. “An outbreak of a disease or illness that spreads rapidly among individuals in an area or population at the same time.”
From the American Heritage Science Dictionary
Confusion of these two words is one reason that claims of an “epidemic of autism” are made: To say that there is “no autism epidemic” is not to say that there is a low prevalence of autism. The prevalence rate of autism is at its highest ever—1 in 166 (see the CDC’s data on ASD Prevalence Questions); the prevalence rate is not the same thing as the actual number of persons diagnosed.
Saying that there is no “epidemic of autism” is not a denial of how many autistic persons there may actually be.
In response to last week’s Time magazine article on whether or not there is an autism epidemic, I heard one parent comment that they did not know a single person with Asperger’s. I do not know much about this parent’s life (aside from the fact that we both have autistic children); I have to say that, with each passing day I spend in Autismland, I recognize that this or or that person I knew in the past and had this or that “different” interaction with may well have Asperger’s syndrome, whether diagnosed or not.
What if autism is under-diagnosed?
Addendum @ 16.39: A recent comment on What if there is no autism epidemic? adds some thoughtful points: “I believe that the number of children who are profoundly disabled, moderately affected, and just atypical in ways we now call the autistic spectrum may not be significantly different than in the past. Maybe more children are affected; the old database isn’t as reliable as recent data.” Go here to read the entire comment.
There are probably parents who would say that, but who don’t KNOW they know someone with Asperger’s Syndrome.
I confine my actions somewhat when I’m with one particular group. Most of them may not suspect anything. (And if anyone does suspect anything, she hasn’t said anything to me. Using “she” because this particular group is all women.) In fact, one who suspects a number of people and listed a few of them off didn’t put me in the list….
With other groups, the people who know what I’m talking about pause, and if they say much of anything, it’s something to the effect of, “Well, that would explain X….”
I think “know” is the key word—-for myself, “KNOWing” what autism is has enabled me to make sense of past experiences and acquaintances; it is not (as a commenter on the Slate article wrote) the new stand-in label for mental retardation.
Epidemic implies contagion. Autism is not contagious.
Several years ago an administrator told me that autism was overtaking Learning disabilities as the number one disability in our district. He felt that improved diagnostics were not enough to explain the increase.