Thursday, October 12, 2006

116.1 in 10, 000 or 1 per 86

Please have a look at this recent study:

“BACKGROUND: Recent reports have suggested that the prevalence of autism and related spectrum disorders (ASDs) is substantially higher than previously recognised. We sought to quantify prevalence of ASDs in children in South Thames, UK. METHODS: Within a total population cohort of 56 946 children aged 9-10 years, we screened all those with a current clinical diagnosis of ASD (n=255) or those judged to be at risk for being an undetected case (n=1515). A stratified subsample (n=255) received a comprehensive diagnostic assessment, including standardised clinical observation, and parent interview assessments of autistic symptoms, language, and intelligence quotient (IQ). Clinical consensus diagnoses of childhood autism and other ASDs were derived. We used a sample weighting procedure to estimate prevalence. FINDINGS: The prevalence of childhood autism was 38.9 per 10,000 (95% CI 29.9-47.8) and that of other ASDs was 77.2 per 10,000 (52.1-102.3), making the total prevalence of all ASDs 116.1 per 10,000 (90.4-141.8). A narrower definition of childhood autism, which combined clinical consensus with instrument criteria for past and current presentation, provided a prevalence of 24.8 per 10,000 (17.6-32.0). The rate of previous local identification was lowest for children of less educated parents. INTERPRETATION: Prevalence of autism and related ASDs is substantially greater than previously recognised. Whether the increase is due to better ascertainment, broadening diagnostic criteria, or increased incidence is unclear. Services in health, education, and social care will need to recognise the needs of children with some form of ASD, who constitute 1% of the child population.”

The older criteria used in the study produced a lower rate of autism which was just outside the confidence intervals (margin of error) for the newer criteria. This is an extremely important finding which has implications for how diagnsotics contributes to autism prevalence. I am surprised the authors did not address this more directly.

Baird, G., Simonoff, E., Pickles, A., Chandler, S., Loucas, T., Meldrum, D. & Charman, T.(2006). Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP). The Lancet, 368, 210-215.


Blogger Joseph said...

Fombonne's thimerosal study out of Canada also found over 1% prevalence for Kindergarten children (diagnosed, not screened). Lorna Wing has also hinted in the past that about 1% is the right number. This is just what is found with good screening, the way the criteria is interpreted in the West at the moment.

It could always go higher if the interpretation is losened. For example, Posserud et al. (2006) found that 2.7% of all children 7-9 y/o were high scorers in the ASSQ. Who's to prevent *all* these children from being diagnosed with ASD?

8:25 AM  
Blogger Interverbal said...

Hi Joseph,

"Who's to prevent *all* these children from being diagnosed with ASD?"

Even though that is a rhetorical question, the answer is "None one but the criteria used in the studies".

10:19 AM  

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