Friday, October 25, 2013

Autism Prevalence Is Now At 1 In 50 Children

The US Centers for Disease Control and Prevention (CDC) has released new figures for autism prevalence in the United States. They now give a prevalence of 1 in 50, but this story, like most autism-related stories, goes deeper than the numbers.

First, this prevalence estimate doesn’t focus only on 8-year-olds, the population used for deriving the 1 in 88 number reported in 2012. Instead, it encompasses the number of diagnosed autistic people walking around in 2011 and 2012 who were ages 6 to 17. The 2007 percentage of the population fitting that description was 1.16%. These new numbers put that value for 2011-2012 at 2%.

From the CDC’s report:

"The magnitude of the increase was greatest for boys and for adolescents aged 14–17. Cohort analyses revealed consistent estimates of both the prevalence of parent-reported ASD (autism spectrum disorder) and autism severity ratings over time. Children who were first diagnosed in or after 2008 accounted for much of the observed prevalence increase among school-aged children (those aged 6–17). School-aged children diagnosed in or in or after 2008 were more likely to have milder ASD and less likely to have severe ASD than those diagnosed in or before 2007".

According to the CDC, hidden within these numbers is the finding that most of the increase from 2007 to now occurred in school-aged children. In other words, given that it’s possible to diagnose autism as early as age 18 months and usually by age 5, many of these new autism diagnoses were in children who received them relatively later. Children who were, therefore, walking around for quite a few years with autism that went unrecognized … and uncounted. That fits with the idea that a lot of the increase in autism we’ve seen in the last decade has much to do with greater awareness and identification.

The CDC’s information comes from parent reports, acquired by random telephone surveys. Parents answered questions about the ASD diagnosis and severity, and the age and year the child was diagnosed. When the CDC did this study in 2007, the results relied on information for 63,967 children; for 2011-2012, that number was slightly higher at 65,556.

From 2007 to 2013, parent-reported autism prevalence increased significantly in all age groups in the 6-17 range and increased for boys from 1.8% to 3.23%. Girls also showed an increase, but not as dramatic, from 0.49% to 0.70%. Autism among children ages 14 to 17 was up more than 1%, compared to children in the youngest, 6 to 9 age group (0.5%). In 2007, this older group, born in the 1990s, was less likely to have ASD than younger children.

Autism severity ratings (or, as a friend of mine analogizes, octane rating) also was revealing. Children ages 2 to 13 in 2007 and diagnosed by that year — and who were thus 6 to 17 in 2011-2012 — showed no changes in ASD severity across years. However, children in the 6 to 17 bracket who were diagnosed after 2007 were more likely to be rated as having “mild” ASD (6.9% for 2011-2012 versus 16.9% for 2007), suggesting that greater awareness and diagnostic capture explain the ASD increase in this group.

The CDC authors observe that the 14% of children ages 14 to 17 who were diagnosed at age 7 or later received their diagnosis “well beyond” the time when autism signs and symptoms become clear. In addition, more than half these children were classified as having “mild” ASD, according to their parents. The CDC authors say,

"Together, these findings suggest that the increase in prevalence of parent-reported ASD may have resulted from improved ascertainment of ASD by doctors and other health care professionals in recent years, especially when the symptoms are mild. Changes in the ascertainment of ASD could occur because of changes in ASD awareness among parents or health care professionals, increased access to diagnostic services, changes in how screening tests or diagnostic criteria are used, or increased special education placements in the community". 
The report concludes:

"Increases in the prevalence of parent-reported ASD continued through 2011–2012, and much  of the recent increase—especially for children aged 6–13—was the result of diagnoses of children with previously unrecognized ASD".
You will probably see a lot of headlines about the 1 in 50. Some organizations might even try to use those numbers to scare people, to talk about an “epidemic” or a “tsunami.” But if you look at the numbers and the report itself, you’ll see that overall, the numbers of people born with autism aren’t necessarily increasing dramatically. It’s just that we’re getting better and better at counting them. The next step is getting better at accepting autistic people, seeing their potential, and ensuring the supports and resources they need to fulfill that potential.



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