In 1995, a group of British researchers published a cohort study in the LancetВ showing that individuals who had been vaccinated with the measles-mumps-rubella vaccine (MMR) were more likely to have bowel disease than individuals who had not received MMR. The story of how vaccines came to be questioned as a cause of autism dates back to the 1990s. Some, however, still question whether vaccines play a role in ASD development, and so the public health and medical establishments continue to address these concerns. Vaccines have perhaps received more scrutiny that any other speculated cause of ASD, and the great majority of scientists, physicians, and public health researchers have come to the conclusion that there is no association between vaccines and autism. The role of vaccines has been questioned, along with other possible risk factors for ASD, such as genetic predisposition, advanced parental age, and other environmental factors. Whether the high rates of autism today are due to increased diagnosis and reporting, changing definitions of autism, or an actual increase in development of ASD is unknown., Regardless, researchers and worried parents alike have speculated about causes of autism, and the issue has been widely studied. Beginning in the 1990s, our understanding of the spectrum of autism has expanded greatly, and now individuals who would most likely previously not have been thought of as having autism may be classified with one of a variety of ASDs. It is difficult to compare autism rates from the 1990s and later with rates from the 1940s through the 1980s: in earlier years, autism was associated primarily with very severely affected individuals and the rate of autism was estimated to be only about 1 in 10,000 people.

For children born in 2004, about 1 in 68 children would receive an ASD diagnosis.

CDC, about 1 in 150 would be diagnosed with an autism spectrum disorder (ASD). For children born in 1992, according to the U.S.

Autism rates in developing countries have risen remarkably in the past 20 years.

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