Yesterday's Sydney Morning Herald (paper edition) carried a front page story titled: 'Males fuel rise of the Ritalin generation' by Amy Corderoy. (See SMH, Fairfax, Monday January 24, 2011, page 1-2.)
The article's Dr Scott, who studied Ritilin use, was quoted as saying: 'About five to 10 percent of the population has ADHD'. He went on to note that girls were often undiagnosed (presumably because they may have the passive sort, often called ADD, which can easily be overlooked as daydreaming, forgetfulness and so forth).
The ten percent diagnostic figure seems to match my limited personal experience teaching in schools. If the department responsible won't give out autism prevalence statistics because of privacy concerns, the education institutions are where its prevalence is arguably most obvious. In most of the handful of classes I taught in, the teachers seemed at a loss to account for the high numbers of children with attention issues. I'm not talking about children who fidget and daydream. These were children who snatched others' books, ran about the room, dived under desks covering their ears against unpleasant noises, failed to form letters properly, ignored instructions, interrupted, disrupted others and seldom completed tasks no matter how rigorously they were brought to attention.
ADHD is usually considered as separate to ASD (or autism spectrum disorders). However Diane Kennedy argues convincingly that ADHD is an ASD (see The ADHD Autism Connectionhttp://www.amazon.co.uk/ADHD-Autism-Connection-Diagnoses-Effective-Treatments/dp/1578564980), and treatments such as the gluten/casein free diet and even chelation have often been described as working for both. The book I used to chelate my girl described the disorders as linked, and also recommended similar treatments for both (see Children with Starving Brains http://www.amazon.com/gp/product/images/188364710X/ref=dp_image_0?ie=UTF8&n=283155&s=books).
One in ten is a terrifying figure if true. Of course, even more terrifying is the prospect that it might be increasing in prevalence. Unfortunately given the absence of a centralised ASD/ADHD counting system (our government leaves it to the States to do their own individual work), nobody is in an ideal position to either notice or recognise a trend.
If you're not already worried, maybe it's time you went into a schoolroom.
Meanwhile, something causes autism.