Price, CS. et.al., Comments by SafeMinds, 17 September 2010
This study was funded by CDC and conducted by several parties with an interest in protecting vaccine use: CDC staff involved in vaccine research and promotion; Abt Associates, a contract research organization whose largest clients include vaccine manufacturers and the CDC’s National Immunization Program; America’s Health Insurance Plans, the trade group for the health insurance industry; and three HMOs which receive substantial funding from vaccine manufacturers to conduct vaccine licensing research. Planning for this study began in 2001. Over the 9 year study period, the large external panel of consultants providing input to the investigators was reduced to a small subset by study end. The original large panel recommended against the study design ultimately employed, as insufficient to answer the question of early thimerosal exposure and autism rates. The CDC and AHIP overruled the external consultants. The paper published this week infinding that increased mercury exposure from thimerosal in vaccines actually decreased the risk of having an autism diagnosis.
There are two primary deficiencies in the study methodology which would lead to the curious finding of a protective, rather than a harmful effect of early thimerosal exposure found in the study. The first deficiency concerns the variables used for stratification and the second concerns the low participation rate leading to sample bias. The stratification scheme would bias the results to the null; the sampling bias would swing the results to show a lower autism rate among those highly exposed. Had these deficiencies been addressed through a better study design, it is equally likely that the results would have in fact shown a harmful effect from early thimerosal exposure.
The study sample did not allow an examination of an exposed versus an unexposed group, or even a high versus a low exposed group, but rather the study mostly examined the effect of timing of exposure on autism rates. There were virtually no subjects who were unvaccinated and few who were truly less vaccinated; rather, the low exposed group was mostly just late relative to the higher exposed group, ie, those vaccinating on time.