Originally Posted by Paul&John

Can be because of:
Changes in the definition of autism, rather than use of the measles, mumps, and rubella vaccine (MMR vaccine), led to increased diagnosis of autism in the United States and probably in Europe, says a study from the Mayo Clinic in Rochester, Minnesota (Archives of Pediatrics and Adolescent Medicine 2005;159:37-44).

Before the late 1980s and early 1990s, these children were diagnosed as retarded or having developmental delay, lead author William Barbaresi, a developmental paediatrician, told the BMJ.

The prevalence of autism increased more than eightfold in the United States, from 5.5 (95% confidence interval 1.4 to 9.5) per 100 000 children in 1980-3 to 44.9 (32.9 to 56.9) per 100 000 in ?
http://www.bmj.com//content/330/7483/112.5