How are the rates for Autism Spectrum Disorder determined?

It seems that every where you turn you can see the rates for Autism Spectrum Disorder (ASD). Recently new rates were released showing an increase to an astonishing 1 in 68 children.
How are these rates determined? What do they actually mean?

The Center for Disease Control set up a national autism monitoring program abbreviated ADDM. This program currently includes eleven sights where they look at the rates of ASD in eight year old children. They do this without ever once having to see a child or talk to a parent. How? The comb through various records including health records, and in some instances school records. They then use this information to estimate the current prevalence rates of ASD.

While a child having an ASD diagnosis is considered when determining the rates, it is not the primary exclusion. Instead the team of researchers also looks at behaviors that can be indicative of ASD, such as solitary play or not initiating play. This means that the rate of 1 in 68 8 year olds does not indicate that 1 in 68 children are actually diagnosed with an ASD diagnosis.

Overall the ADDM sites looked at records for 363,749 children in Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Utah, and Wisconsin.

One in 42 boys were determined to have ASD compared to 1 in 189 girls. This increases the gender gap to a 1 to 4.5 gap as apposed to previous 1 in 4 gap. In addition more White male children were found to have an ASD then any other race. I wonder how this would be effected if California were to be included as an ADDM collection site.

Overall the disparity in diagnosis is concerning. It suggests that either girls are at less risk for ASD, while boys are at increasing risk, or that the disparity in diagnosis due to gender is increasing. While I do think that there is cause to believe that there may be gender differences in ASD, I also see evidence of a disparity in diagnosis - including the increasing gap between diagnosis while ASD rates continue to rise.

The disparity in ASD diagnosis in regards to race is also alarming. However, this may be impacted by the overabundance of White eight year olds included in the study. The overall sample size consisted of 55.3% White Non-Hispanic, 20.9% Black Non-Hispanic, 18.9% Hispanic, 4.3% Asian Pacific Islander, and 0.6% American Indian/Alaskan Native. This disparity may have more to do with socioeconomic status then an actual biological race based phenomenon. Once again I wonder how this would be impacted if California were to be included as a collection site.

The data was officially collected in 2010, with the report being released in 2014. As such diagnostic criteria was based on the DSM-IV spectrum criteria. This includes Autism, Asperger's and PDD-NOs as options for diagnosis. As collection continues the study plans on using both the DSM-V criteria and the DSM-IV criteria and comparing the impact between the two.

Reference

CDC. (2014). Prevalence of autism spectrum disorder among children aged 8 years - Autism and developmental disabilities monitoring network, 11 sites, United States, 2010. Surveillance Summaries, 63, 2, 1-21.

This article can be found here.