We used data sets from Denmark, California, Japan, and a worldwide composite of studies. In the Danish, California, and worldwide data sets, we found that an increase in AD cumulative incidence began about 1988-1989. The Japanese study (1988-1996) had AD cumulative incidence increasing continuously, and no changepoint year could be calculated. Although the debate about the nature of increasing autism continues, the potential for this increase to be real and involve exogenous environmental stressors exists. The timing of an increase in autism incidence may help in screening for potential candidate environmental stressors.The study is careful not to point to vaccines:
Subsequent studies on MMR vaccine and thimerosal-containing vaccines did not support a relationship with autism. In a 2004 report, the Immunization Safety Committee of the Institute of Medicine determined that the body of epidemiological evidence favors rejection of a causal relationship between either MMR or thimerosal containing vaccines and autism. Work on tetrachlorethylene, trichloroethylene, and trihalomethanes in drinking water also has not supported a relationship with autism. Certain airborne metals and solvents still require confirmation of any relationship to autism. New research studies are continuing to evaluate other possible environmental factors.