Ontario Adult Autism Research and Support Network - OAARSN

How Many People Have Autism?

Key studies in the 1960s, in sample regions in different parts of the world, found a ratio of 4.5 per 10,000 of the child population to have Autistic Disorder (classic Autism or Kanner syndrome). By around 1990, a further 15 in every 10,000 were estimated to have what were called, in North America, other pervasive developmental disorders (PDD).

Research in the 1990s developed the concept of Autism Spectrum Disorder (ASD), with the aim of including people who might have some but not all the key diagnostic features. British studies of sample regions estimated that 71 in every 10,000 had a milder form of ASD, mainly affecting social relationships rather than communication and language. About half of this larger number (36 in every 10,000 of the population) was estimated to have Asperger’s Syndrome. These figures add up to 91 persons in every 10,000, nearly one per cent of the total population, which is the prevalence usually cited for the United Kingdom. At this rate, more than 60 million people around the world have some form of Autism. 

In whole countries, such data are estimates rather than actual counts of people diagnosed. It is likely that many on the Autism spectrum have not been formally identified, especially adults. Prevalence figures of one person in 150 or one in 166 are quoted in North America. Applying the rate of one in 150 to age-groups of Ontario’s population at the 2001 census, we conservatively estimated 20,000 children aged 0-19 and 56,000 adults aged 20 and over.

Autism affects families in all races, cultures and socioeconomic groups and is found everywhere in the world. More males than females are affected, the ratio being 4:1 with Autistic Disorder (classic Autism), 9:1 with Asperger’s Syndrome.

Is the prevalence of Autism increasing? Some advocates for services to young children describe the increased diagnoses of some form of Autism since the 1990s as an explosion, even a pandemic. In part, this probably reflects an enormous increase in awareness of Autism, so that professionals and parents now recognize the symptoms of ASD much more readily than they did. Another factor is the widening of criteria from Autistic Disorder or classic Autism, to include the much broader concept of an Autism spectrum including Asperger’s Syndrome as well as people who combine Autism with some other disability. Perhaps there has also been a real increase in the numbers and proportions of affected people—related to a wide range of environmental toxins and viral infections.

Does the prevalence of Autism vary from place to place? Autism has been found all over the world, in all societies and cultures, and in people of all ethnic and socio-economic groups. Some localities have been found to have very high concentrations of ASD diagnoses. Since 2000, the volume of funded research into genetic, environmental and biomedical factors in Autism has increased enormously, but we are not yet able to answer these questions with certainty.