Since so much of the controversy regarding autism is centered around a possible link to vaccines, I decided to compare the autism percentage rate to the recommended childhood vaccine schedule's history. You can see that as the number of vaccines increased (most notably the aluminum-containing shots), so did the percentage of individuals with autism. Most compelling of all, there was no increase in the percentage of autism cases in 2002-2004, when no vaccines were added to the childhood schedule.
The vaccines highlighted in yellow contain aluminum.
The Measels, OPV, Varicella, and Rotavirus vaccines are live-virus vaccines.
* The percentages were calculated by dividing the number of individuals who were diagnosed with autism by the total number of live births for each time period. I could not calculate the percentages for the first three time periods b/c the oldest live birth data I have is for 1960. So I just typed in the number of individuals.
** Pregnant women were still recommended to receive the flu shot, which contains thimerosal, even after thimerosal had been reduced from the newly manufactured children's vaccines in 2001.
** When the levels were ACTUALLY reduced is uncertain. According to this Imus interview with David Kirby Here, the vaccine manufactures stopped producing the shots that contained the full amount of thimerosal in 2001. They never recalled the existing thimerosal-containing vaccines because the decision make vaccines with no or lower levels of thimerosal was just "precautionary". A similar problem happened when the polio vaccine was found to contain the SV40 virus. Accoring to the CDC's website, "In 1961, the virus was found to cause tumors in rodents (Eddy et al., 1961). That same year, the federal government required that new stocks of polio vaccine be free of SV40. However, existing polio vaccine stocks were not recalled and were used until 1963." So based on that example, it's very possible that many vaccines still contained the higher levels of thimerosal until at least 2003.
Further explanation of the Required Shots mentioned on the chart above:
* 1977 - "No Shots, No School"
10/14/1977 Bulletin 15 Nationwide Immunization Program led to a large increase in vaccinated children. President Carter, through Joseph A. Califano, Jr., Secretary of Health, Education and Welfare, launched a national campaign to immunize the 20 million children under the age of 15 who were not fully vaccinated, and he established a permanent system to increase immunity levels of 90% or better.
* 1978 - Shots were first required for Daycare centers. "New regulations required that all children attending daycare centers be vaccinated against diphtheria, tetanus, pertussis, polio, measles and rubella. Tremendous cooperation was received from all daycare center operators, and of course, from the parents."
* New School Requirements established by the Clinton administration on Dec 26, 2000 included Mumps, Hib, Hep A, Hep B, and Varicella. 
The risk of prenatal thimerosal exposure:
One CDC study found that, among males, increased prenatal exposure to thimerosal was associated with, "poorer performance with attention and executive functioning"  There was a large increase in the autism percentage rate when the flu shot was first recommended for pregnant women. The prenatal flu shot was first recommended in August 1997, and there was a huge jump in the autism percentage rate when you compare the 1994-1997 time period with the 1998-2001 time period. This increase might suggest that prenatal flu shots are an unsafe practice [4 see disclaimer about expecting mothers with asthma], and the CDC's study could help explain the higher prevalence of autism in boys.
The risk of aluminum in vaccines:
I believe that another contributing factor for the increases in the autism percentage rate is the aluminum-containing vaccines. As you can see on the chart, each time a new aluminum-containing vaccine was added, the autism percentage rate increased. In 1983 infants received 3 doses of aluminum containing shots by 6 months, and now in 2008 infants receive 13 doses of aluminum containing shots by 6 months of age. Page 335 of a document on on TACA Now's website shows a chart that illustrates the increase in the number of doses of aluminum-containing vaccines (received by 18 months of age) from 1970 to 2007. If you were to overlay the data on their chart with the autism percentages on the chart on this blog, you'd see how they increase in correlation with one another. The most alarming problem with aluminum in my opinion is the Hep B vaccine that is given to newborns. The FDA's limit of 25 mcg for an injectable solution was set, in part, because aluminum-containing medical treatments were causing neurological delays in premature babies. This is believed to be due to an underdeveloped kidney function in premature babies. The 250 mcg Hep B vaccine is offered to all newborns, INCLUDING premature babies. Several studies have found that very premature babies have an increased risk of autism . I personally think this correlation is connected to the aluminum in vaccines. Unless the baby's mother has Hep B, infants are at a very low risk of contracting this disease. So in my opinion, this shot should not be given to newborns, especially preemies, unless the mom has Hep B . Even though correlation does not prove causation, I think this correlation does warrant more research regarding the safety of using aluminum compounds as vaccine adjuvants.
Here's my personal hypothesis that I hope some non-biased researcher will test: Based on the studies I've cited and the matching correlations reflected in the chart above, I think that the prenatal flu shot plays a significant role in the cases of classic autism where the child has symptoms from birth, and I believe that aluminum is responsible for a significant number of regressive autism cases because aluminum causes dementia in kidney dialysis patients and although it is still controversial there is a link between Alzheimer's disease and aluminum. With Alzheimer's disease, dialysis dementia, and regressive autism, the patients loose previously acquired skills. I specifically stated that I think these factors are responsible for a significant portion (but not entirely responsible) because there are other known risk factors such as prenatal exposure to certain toxins and because live virus vaccines don't contain aluminum, but they have still been known to cause encephalitis and seizures which can also be harmful.
Side note on the reduced thimerosal levels:
An article on the Age of Autism website brilliantly points out that when a person is allergic to something such as peanuts, it only takes a trace amount to cause a severe reaction. So even though it is my personal hypothesis that aluminum is more responsible for the regressive cases, I still don't think that using thimerosal in childhood vaccines is a good idea either. Both because it is a known neurotoxin and it is believed to lower glutathione levels and glutathione is used by the body to fight viruses and remove toxins such as aluminum. I think it's also interesting to note that food processing plants post warning labels (on foods that don't even contain peanuts) that let the consumer know that the food was processed in a plant that also processes peanuts. By contrast, doctors tell us that vaccines with trace amounts of thimerosal (which do contain thimerosal as an ingredient) contain no thimerosal. There seems to be a lot of bias in the medical community to avoid admitting any possible flaw or bad reactions to vaccines. I highly suggest reading the whole Age of Autism article. www.ageofautism.com/2008/09/an-autism-moms.html
 Autism percentages were derived from the Individuals with Autism data on TACA Now, and the total number of live births in California.
[4 Disclaimer] The risks vs the benefits are different for everyone so always ask your doctor before making any medical decision.