The report for 2014 focused on 42,644 children in 11 states (Arizona, Arkansas, Colorado, Georgia, Maryland, Minnesota, Missouri, New Jersey, North Carolina, Tennessee and Wisconsin). Researchers determined that 5,473 of these kids met the definition for an autism spectrum disorder.
Since the data come from select sites where researchers are able to conduct a thorough analysis, the findings are not necessarily representative of the nation as a whole. But experts value them because they are more comprehensive than the results from other surveys that rely on interviews with parents.
The new study appears in Friday’s edition of the CDC’s Morbidity and Mortality Weekly Report. Here’s a summary of the findings:
Out of every 1,000 8-year-olds in the ADDM study, 16.8 had an autism spectrum disorder. That works out to 1 in 59 kids included in the analysis for 2014, or 1.7%.
Those figures represent a slight increase from the previous ADDM report, which found that 1 in 68 8-year-olds had ASD in 2012.
Six of the 11 sites in the new study also participated in the last one. In these states, the prevalence of ASD was 20% higher in 2014 than it was in 2012.
Back in 2000, when the first ADDM study began, only 1 out of every 150 8-year-olds was identified with ASD.
The prevalence of autism spectrum disorders for boys (26.6 cases per 1,000 boys) was four times higher than for girls (6.6 cases per 1,000 girls).
This gender gap was seen in each of the 11 study areas, though the magnitude varied by state. In Arizona, the prevalence for boys was 3.2 times higher than for girls. At the other end of the spectrum was Georgia, where it was 4.9 times higher for boys than for girls.
Autism spectrum disorders were most common in New Jersey, where researchers identified 29.3 cases for every 1,000 8-year-olds. Minnesota came in second, with 24 cases per 1,000 kids.
The state with the lowest prevalence in the study was Arkansas, with 13.1 cases per 1,000 8-year-olds. Four other states were close to that mark: Colorado (13.9 per 1,000), Arizona (14 per 1,000), Missouri (14.1 per 1,000) and Wisconsin (14.1 per 1,000).
White children were still the most likely to meet the definition for ASD. In the 11 states combined, 17.2 of every 1,000 white 8-year-olds had the disorder, compared with 16 of every 1,000 black children, 14 of every 1,000 Latino children and 13.5 of every 1,000 Asian and Pacific Islander children.
Racial disparities between white and black children were statistically significant in three states (Arkansas, Missouri and Wisconsin). Racial disparities between white and Latino children were statistically significant in seven states (Arizona, Arkansas, Colorado, Georgia, Missouri, North Carolina and Tennessee).
New Jersey, the state where ASD was most common, had “almost no difference” in prevalence for white, black and Latino children, the study authors noted. For all three groups, the prevalence ranged from 26.8 to 30.2 cases per 1,000 children — differences that were too small to be statistically significant.
The researchers took this as a sign that when the accounting of ASD is more complete, differences between groups will either narrow or disappear altogether. That should help make ASD therapies and services available to all children who need them, they added.
Nine of the sites examined data on children’s intellectual ability. This revealed that 31% of the 8-year-olds with ASD had an IQ less than or equal to 70, which qualified them as having an intellectual disability. An additional 25% were in the “borderline” range (with an IQ between 71 and 85), and 44% had average or above-average intelligence.
Overall, girls with ASD were more likely than boys to be categorized as intellectually disabled, while boys were more likely than girls to find themselves in the average or above-average range.
Among the 8-year-olds with ASD, 22% of white children, 35% of Latino children and 44% of black children had an IQ at or below 70.
Some records that researchers looked for could not be found. If they had been included in the analysis, the study authors estimate that the prevalence of ASD would have been nearly 20% higher in Arkansas and Tennessee, about 8% higher in Maryland and up to 5% higher in Colorado, Missouri, New Jersey and North Carolina.
Psychiatrists officially changed the definition of autism spectrum disorder when they rewrote the Diagnostic and Statistical Manual of Mental Disorders in 2013. Researchers applied the new criteria to a subset of the children in the study, along with the older criteria they had been using since 2000.
The new definition is likely to translate into fewer cases of ASD, the study authors wrote. For instance, estimates based on the new criteria were about 3% lower for boys and 6% lower for girls. They also were 3% lower for white and black children, 5% lower for Asian children and 8% lower for Latino children..