I bring this up because there is a common argument that the autism “rates” in places like Denmark and Sweden are much lower than those in the US and elsewhere. This is used to try to negate studies using those country’s populations in, for example, showing that there is no increased risk from thimerosal or the MMR vaccine. This error often stems from comparing “incidence” to “prevalence”.
Is the autism prevalence low in Denmark? Not really. This paper just out (and other reports previously, including this one cited by Steven Novella) show a prevalence pretty comparable to the US.
J Autism Dev Disord. 2011 Feb 11. [Epub ahead of print]
A Comparison of Autism Prevalence Trends in Denmark and Western Australia.
Parner ET, Thorsen P, Dixon G, de Klerk N, Leonard H, Nassar N, Bourke J, Bower C, Glasson EJ.
Institute of Public Health, Department of Biostatistics, University of Aarhus, Aarhus, Denmark.
Prevalence statistics for autism spectrum disorders (ASD) vary widely across geographical boundaries. Some variation can be explained by diagnostic methods, case ascertainment and age at diagnosis. This study compared prevalence statistics for two distinct geographical regions, Denmark and Western Australia, both of which have had population-based registers and consistent classification systems operating over the past decade. Overall ASD prevalence rates were higher in Denmark (68.5 per 10,000 children) compared with Western Australia (51.0 per 10,000 children), while the diagnosis of childhood autism was more prevalent in Western Australia (39.3 per 10,000 children) compared with Denmark (21.8 per 10,000 children). These differences are probably caused by local phenomena affecting case ascertainment but influence from biological or geographical factors may exist.
Prevalence of 68.5 per 10,000 children. A previous estimate was 80 per 10,000. Generation Rescue claimed a rate of 1 in 2200 (4.5 per 10,000) when they tried to make the case that…oh I bet you can guess…that vaccines cause autism. The 1 in 80 figure was already published, so I doubt they will change their story given yet another study.