6.8 1960s–2010s: prevalence of autism in the population
Prevalence means the number of individuals affected by a condition at a given time. Measuring autism prevalence depends on estimating how many individuals in a population have a symptom profile that fits the diagnosis. When autism was first identified it seemed to be rare. In 1966, Lotter estimated that childhood autism affected 4 children in 10,000. In the late 1970s, and adopting a wider definition of autism, Lorna Wing and Judith Gould (Wing and Gould, 1979) scrutinised the medical and social services records of 35,000 children in Camberwell for likely cases of autism. Their prevalence estimate was 21 children in 10,000, of whom 5 would have ‘classic autism’, while the rest were somewhere on a ‘spectrum’ – which was becoming an increasingly relevant concept to all working on autism. Notice how prevalence estimates changed as the definition of autism (i.e. the inclusion criteria) was broadened. With further research and clinical advances leading to even broader criteria and more widespread diagnosis, it is currently estimated that at least 1 in 100 individuals in the UK may be on the autism spectrum. A recent worldwide estimate, based on prevalence studies in different countries, is somewhat lower. But where awareness of autism and diagnostic services are limited, estimates of prevalence are inevitably lower. For some parts of the world (for instance many African countries) where diagnosis is barely available, prevalence cannot be reliably estimated. You will read more about this in Weeks 3 and 8.