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Recent autism prevalence studies point to variability in methodology and bias

Posted Feb 08 2011 2:00am

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.

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.
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.
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.
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.

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.

  1. Tweets that mention Autism Blog - Recent autism prevalence studies point to variability in methodology and bias « Left Brain/Right Brain --
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  2. All About Developmental Disabilities: A Message from Rita Young, Dir. of Public Policy & Education | Georgia Community Support & Solutions:
    [...] Recent autism prevalence studies point to variability in methodology and bias ( [...]
  3. AWOL:
    AUTISM DATA The following data is compiled from the US Individuals With Disabilities Education Act data. The data is State-collected, and shows totals of US young people age 6-21 in full time education with a formal diagnosis of DSM-IV autism. The total is updated year on year, so is a “rolling total” within that age-band, not a cumulative total, which will be well in excess of these figures. Year/Students 1994 22,780 1995 28,813 1996 34,082 1997 42,487 1998 53,561 1999 65,391 2000 78,717 2001 97,847 2002 118,603 2003 140,920 2004 166,302 2005 193,481 2006 224,415 2007 258,095 2008 294,302 2009 335,199 Increase 1994-2009 (22,780 vs 335,199) 14.7-fold increase in 15 years Increase 2008-2009 (294,302 vs 335,199) 13.9% increase in one year If a 13.9% increase was applied to the 2009 figure, this would give a provisional estimate for 2010 of 382,000. If a further increase was applied to this provisional 2010 estimate, this would give a provisional estimate for 2011 of 435,000. The population of the United States is approximately 312m, and of the UK (mid-2009) is 62m. The population of the UK is therefore approximately 20% of that of the US. The health regimes of the two countries are broadly similar, and so applying a 20% estimate to US autism figures (for young people age 6-21 in full time education) would give a UK estimate for 2011 of 87,000. For UK costs, including loss of tax revenue of parents, loss of gdp of parents (both during years of caring), loss of tax revenue of young people, loss of gdp of young people (both lifelong), costs of provision of day care, costs of transport, and costs of allowances such as Independent Living Fund, a total of £5m for lifelong costs (per autistic person affected) has been estimated. The actual costs in each case will vary below or above this figure. But taking an estimate of £5m, and applying this only to the age 6-21 population cohort, (i.e. completely ignoring younger and older cases), this gives a lifelong total UK cost to the community of £435 billion (87,000 multiplied by £5m). The actual total may be well in excess of this figure when one includes other age groups. SCOTTISH AUTISM DATA Unlike England, Scotland systematically collects data on autism amongst school age children and young people as part of its education database, and has been doing so since 1998. The data suggest a steady and steep rise in numbers: (Year) (Autism) 1998 820 1999 959 2000 1,245 2001 1,515 2002 2,204 For the years from 2003 onwards, data collected for autism has been paralleled by data for children “with significant language and speech disorder” (SL&SD). Both show a steep rise in a short time: (Year) (Autism) (SL&SD) (Autism + SL&SD) 2003 2,663 1,440 4,103 2004 3,090 1,514 4,604 2005 3484 1,679 5,163 2006 4,051 2,987 7,038 2007 4,550 3,723 8,273 2008 4,900 4,415 9,315 2009 5,254 4,754 10,008 The number of children in education in Scotland with autism for 2009 represents 6.4 times the 1998 figure. The 2010 data is not yet available. The steep parallel increase in children with significant language and speech disorders, alongside the autism increase, may also represent a warning sign of an underlying problem. The increase in SL&SD also suggests that the increase in autism is not significantly (or at all?) due to re-assignment of SL&SD cases into the autism category, as both have risen very steeply in a short time.
  4. Kev:
    Got a link to that Scottish data please AWOL?
  5. Joseph:
    @AWOL: And do you have the data on SLD and MR for IDEA, same period? Please do the calculation dividing it by each year's population size. If you decline this request, I think we'll be justified in assuming that either (1) you did not like the results, or (2) you prefer to ignore the data.

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