Professor David Skuse explains that although it is difficult to calculate the exact proportion of individuals with autism, estimates put the figure at about 0.6 percent.
So, what proportion of people have autism? One of the difficulties there is, it’s like saying, what proportion of people are tall? It all depends on what you call tall. So, is tall over six foot, six foot six? Depending on where you take that threshold, then that’s what you’re going to call tall. And if you think about this, then you think, well this is a rather pointless question, but it is not entirely pointless because if you are very tall it can be a handicap. If you’re over seven foot tall, unless you are going to be a basketball player, you probably find life a little hard. The world was not designed for people who are seven foot tall.
Therefore, having an extreme trait can be a problem and I suggested that people with autism, who have many symptoms of autism, even though they may wish to make social relationships with other people, tend to get rejected, tend to find this exceptionally difficult. This may make them quite upset and indeed lead to their withdrawing into themselves and not trying anymore.
So, how much autism do you have to have to be regarded as a case of autism? Well, we’ve got ways of defining what we call "autism," which are very well standardized across the world so that people who are doing studies in the UK, or in the US, or in France, or in China will mean the same thing by "autism" and for all those studies it would appear that significant autistic symptoms are present in about 0.6 of a percent of children. So, in other words, about sixty per ten thousand would have significant autistic symptomatology on current estimates.