when did autism start to rise

The rise in autism prevalence started becoming noticeable in the late 1980s and 1990s with dramatic increases in diagnosed cases globally, largely attributed to the expansion of diagnostic criteria and the adoption of the autism spectrum concept. Early studies in the 1960s and 1970s showed autism as a rare disorder with prevalence estimates of 2 to 4 per 10,000 children, but by 2002, this had increased to about 6 to 7 per 1,000 children. The increase continued into the 1990s and 2000s, with autism diagnoses rising notably in places like California, where incidence increased 7 to 8-fold from the early 1990s to the early 2000s. Factors contributing to this rise include broader diagnostic criteria, diagnostic substitution (reclassifying children from intellectual disability to autism), earlier age of diagnosis, increased awareness, better screening, and possibly some increases in risk factors like parental age. Although these factors explain much of the rise, there remains a possibility of a true increase in incidence which deserves further investigation. Today, autism prevalence in the U.S. is about 1 in 31 children, a steady increase from past decades where it was much lower (1 in 150 or 1 in 500).