Recent autism prevalence studies point to variability in methodology and bias

In Prevalence of autism spectrum disorders and influence of country of measurement and ethnicity , the authors look at ASD prevalence by country and ethnicity. They hypothesize that “methodological factors, socioeconomic variables, and bias” play a role in the variability in autism prevalence.

The disparities by geography and by ethnicity within the data reported within the U.S. has been a big concern of mine for some time. Clearly there is not an obvious difference between, say, New Jersey (with an estimated prevalence of 10.6/1,000) and Alabama (with an estimated prevalence of 6/1,000) to account for the large difference in estimated prevalence.

Background
The prevalence of autism spectrum disorders (ASD) is generally somewhat lower in countries outside of North America and Europe. While there are culture-specific patterns of social cognitive processing, the influence of such patterns upon ASD prevalence has yet to be fully explored.
Methods
A comprehensive literature search for original articles reporting ASD prevalence was undertaken. Data across studies were compared with a particular focus on variables of geographic residence and ethnicity.
Results
ASD prevalence varies across countries in a manner that appears to suggest that the greatest influence is due to methodological variables. The nature of a potential influence of culture-specific patterns of cognitive processing upon prevalence remains unknown. The available little data concerning the association between ethnicity and prevalence are limited to studies within the United States (US) showing differences in children of Hispanic descent relative to Whites, a finding for which a definitive explanation is lacking.
Conclusions
Available evidence suggests that methodological factors are largely responsible for differences in ASD prevalence across studies. The much discussed increase in prevalence in ASD has been observed worldwide, suggesting that the refinement of diagnostic methodology and/or broadening diagnostic concept is not limited to Western countries. Within individual countries, only in the US has the influence of ethnicity upon ASD prevalence been examined in depth. In the US, children of Hispanic descent have the lowest prevalence of ASD, while Whites tend to have the highest prevalence of ASD. Hypothesized etiological factors for such prevalence differences include methodological factors, socioeconomic variables, and bias.

In Racial Disparities in Community Identification of Autism Spectrum Disorders Over Time; Metropolitan Atlanta, Georgia, 2000-2006. African American (non Hispanic Black) students are less likely than Non Hispanic White students to be identified with “less severe” ASD’s. This even after controlling for socioeconomic status.

Racial Disparities in Community Identification of Autism Spectrum Disorders Over Time; Metropolitan Atlanta, Georgia, 2000-2006.

Jarquin VG, Wiggins LD, Schieve LA, Van Naarden-Braun K.

From the Division of Birth Defects and Developmental Disabilities, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, GA.
Abstract

OBJECTIVE: Past research indicates that non-Hispanic black (NHB) children are less likely than non-Hispanic white (NHW) children to have an autism spectrum disorder (ASD) diagnosis, even if they seem to meet criteria for the disorder. This study examined differences in community identification of ASDs between NHB and NHW children identified by a population-based surveillance system.

METHODS: Participants were identified as an ASD surveillance case by the Metropolitan Atlanta Developmental Disabilities Surveillance Program in surveillance years 2000, 2002, 2004, and 2006. Health and education records were abstracted and reviewed to determine ASD surveillance case status; community identification was defined by a documented ASD diagnosis, special education eligibility, and behaviors noted in records. Children were placed in 1 of 5 mutually exclusive categories on the basis of ASD specificity.

RESULTS: Total ASD prevalence was higher for NHW than NHB children, but NHB children were more likely than NHW children to have autistic disorder and autism eligibility at a public school documented in records. NHB children were less likely than NHW children to have pervasive developmental disorder-not otherwise specified and Asperger’s disorder documented in records, even after controlling for socioeconomic status. NHB children were more likely than NHW children to have co-occurring intellectual disability.

CONCLUSION: NHB children were less likely than NHW children to have been identified with less severe ASDs, which might have prevented or delayed intervention services that would have catered to their needs. This study illustrates the need for continued professional education, particularly concerning milder ASDs in minority groups.

As a society, we have decided that autistic students often need educational supports distinct from those of children with other disabilities. Clearly if we are to serve our students appropriately, we should be accurately identifying each student’s disability (where they exist). The fact that we are not uniform in identifying autistic students indicates that we have far to go in this regard.