In the last four decades the reported prevalence of autism spectrum disorder has increased substantially. The condition was considered rare in the 1970s, affecting fewer than 0.05% of the population, but it is now generally agreed that the lifetime prevalence is at least 1% in both young people and adults.
A study of Swedish children published in the British Medical Journal has found that the prevalence of the autism symptom phenotype has remained stable in children over 10 years, while the official prevalence for registered, clinically diagnosed, autism spectrum disorder has increased substantially.
This suggests that increases in clinical diagnoses of the disorder, rather than an actual increase in prevalence due to factors affecting the pathogenesis, are important for the increase in reported prevalence.
Studies in the past have investigated the potential reasons behind the rise, from environmental impacts to the highly controversial and widely debunked 1998 Andrew Wakefield paper claiming a link between the MMR vaccine and autism.