Over the past 30 years, the number of reported cases of autism has increased rapidly in all countries where prevalence studies have been conducted.
This increase is partly a result of:
- increased awareness of autism among health care professionals, parents and the broader population;
- changes to the diagnostic criteria for autism;
- children being diagnosed at a younger age;
- demographic and geographical variables.
It is also possible that environmental factors contribute to the increased prevalence of autism, though this requires further research.
Some studies have found higher and lower prevalence rates of autism. This is to be expected, given that prevalence studies vary in their scientific method and most are based on a limited sample of a country’s population, rather than on national statistics.
* Elsabbagh et al. 2012; Fombonne, 2011; ADDM 2012; Mattila et al. 2011; Saemundsen et al. 2013; Baird et al. 2011.