- The study used too few cases to make any generalizations about the causes of autism; only 12 children were included in the study. Further, the cases were referred to the researchers and may not be a representative sample of cases of autism.
- There were no healthy control children for comparison. As a result, it is difficult to determine whether the bowel changes seen in the 12 children included in the study were similar to changes in normal children, or to determine if the rate of vaccination in autistic children was higher than in the general population.
- The study did not identify the time period during which the cases were identified.
- In at least 4 of the 12 cases, behavioral problems appeared before the onset of symptoms of bowel disease; that is, the effect preceded the proposed cause. It is unlikely therefore, that bowel disease or the MMR vaccine triggered the autism.
Q: What about the claim that autism has been increasing since the MMR vaccine has been in use?
A: Data from California's Department of Developmental Services has been used to illustrate an increase in cases of autism since the introduction of MMR vaccine. However, the data has been presented inaccurately. For instance:
- The figures presented are based on numbers, not rates and do not account for population growth and changes in the composition of the population
- Changes in diagnostic definitions were not controlled in the report
- As in other areas of the country, children with autism are currently being diagnosed at earlier ages meaning that there will be an increase in the number of reported cases