Autism is found throughout the world in families of all racial, ethnic, and social backgrounds. Autism is four times more likely to be found in boys than in girls.
The number of children diagnosed with autism has increased significantly over the last few decades. According to the Autism Society of Canada, only one in every 10,000 children was diagnosed with autism twenty years ago. Now, the rate appears to be at least one in every 150 births in Canada. Some of this increase can be explained by improved awareness and better diagnosis, while another portion may be explained by environmental factors. The increase in the prevalence of autism cannot be ascribed to genetic factors alone.