A new study published (officially) tomorrow discusses ‘Prevalence of autism-spectrum conditions: UK school-based population study’.
Its an interesting study for quite a few reasons. Firstly, it offers a new autism prevalence of 1.5% (1 in 66). That’s the message that the press will no doubt focus on (and, as Kristina blogs, already have). And I’ve absolutely no doubt that our friends from JABS, Age of Autism and various other anti-vaccine fringe groups will be painting this as part of their ‘evidence’ that we’re in the throes of a massive autism ‘epidemic’.
However, the paper itself is very nuanced and is clear in its messages. However, to be absolutely sure I was correct in the conclusions I drew I had an email conversation with Professor Baron-Cohen before writing this entry.
Point 1: This study confirms the baseline rate of 1% as asserted by the Baird et al paper
Baird et al (2006) asserted that their findings would offer a baseline rate of autism prevalence, that prevalence being 1%. This figure was ascertained by looking at a SEN population of a South Thames cohort. Baron-Cohen et al (2009) confirmed that figure:
These authors took the decision to screen only the ‘at-risk’ population and assert that their estimate should be regarded as the minimum figure. Our results from screening the entire school-aged population support this assertion…
In other words Baron-Cohen et al also looked at the ‘at risk’ population and also found a prevalence of 1%.
Point 2: Baron-Cohen et al identify a further 0.5% to make a total prevalence of 1.5%
What is different about the Baron-Cohen paper is that as well as looking at the ‘at risk’ group they _also_ looked at mainstream schools. Using the CAST screening tool, this study identified a previously unknown prevalence of 0.5% within this mainstream environment.
Our results from screening the entire school-aged population…highlights the reality that there are children with autism- spectrum conditions, notably children with high-functioning autism, who remain undetected in primary schools. These children may use strategies to mask their social and communication difficulties such as going to the computer room at playtime. They may be quiet and cooperative at school and not difficult to manage and therefore teachers may not be aware that they have difficulties. Primary schools in the UK are typically small and foster a supportive and nurturing environment. It may not be until these children move to secondary school that their true differences are revealed.
Often I have heard people asking how it is possible that people with autism could possibly be missed. The Baron-Cohen et al paper gives a graphic answer to that question.
Point 3: Caution should be applied in assuming that results ascertained in Cambridgeshire could be applied across the rest of the country
The area is very affluent within the UK and has excellent autism resources for autistic children. It is a given that many families have moved into the area to try and exploit those services. This would have a positive effect on prevalence that is not consistent with the majority of the UK.
Our study does not report on migration of families but given the level of services for and awareness of autism-spectrum conditions in Cambridgeshire, this remains a distinct possibility. Caution should therefore be employed in assuming that the figures reported here can be applied nationwide.
Professor Baron-Cohen and I had the following exchange about the autism ‘epidemic’:
KL: What would you say to someone who says that your paper is strong evidence of an ‘autism epidemic’ (because you know they will)?
SBC: I think the term ‘epidemic’ of most value in relation to contagious diseases, which autism is not.
KL: Can I rephrase my question? Would you say your findings support the idea that there has been a true rise in prevalence? As oppose to the seven items you say have caused a seeming rise in autism earlier in your paper?
SBC: There has been a real rise in prevalence but what is at issue are the causes of this rise. In the paper we summarize the quite ordinary factors that might have driven the rise, such as better recognition, growth of services, and widening diagnostic criteria.
So next time someone who likes to bandy about the phrase ‘epidemic denier’ like he knows what he’s talking about when he claims that the ‘epidemic deniers’ say that autism is just better recognised these days, tell him there’s a lot more than just one reason:
Prevalence estimates for autism-spectrum conditions have shown a steady increase over the past four decades. In 1978, the consensus estimate for classic autism was 4 in 10 000; today autism-spectrum conditions (including classic autism) affect approximately 1% of the population. This massive increase is likely to reflect seven factors: improved recognition and detection; changes in study methodology; an increase in available diagnostic services; increased awareness among professionals and parents; growing acceptance that autism can coexist with a range of other conditions; and a widening of the diagnostic criteria.