National Academies Press: OpenBook
« Previous: Plausibility Assessment
Suggested Citation:"Causality Argument." Institute of Medicine. 2001. Immunization Safety Review: Thimerosal-Containing Vaccines and Neurodevelopmental Disorders. Washington, DC: The National Academies Press. doi: 10.17226/10208.
×
Page65

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

THIMEROSAL-CONTAINING VACCINES 65 pothesis that mercury exposure had a direct role in an increasing incidence of autism in the 1990s. As noted in previous IOM reports (IOM, 1994 a,b, 2001), a positive eco- logical correlation constitutes only weak evidence of causality, and additional research would be needed to establish a causal association. In addition, the ap- propriateness of the transformation of the cross-sectional autism-caseload data into birth-cohort prevalence data, as was done in this analysis, is questionable. The data used in this analysis are cross-sectional and reflect the number of chil- dren with a diagnosis of autism who are registered in the California Develop- mental Services system. Transforming the cross-sectional data by dividing by birth cohort, creates the artificial impression of a cohort effect when the data are cross-sectional in nature (Fombonne, 2001a). Furthermore, the authors of a re- port on the California autism caseload data stress that their study was not de- signed to measure trends in autism and that the data should therefore be inter- preted with caution (California Department of Developmental Services, 1999~. The analytical value of the data is limited by the inability to account for any changes over time in diagnostic concepts, case definitions, or age of diagnosis (Fombonne, 2001a). As a result, the committee cannot assess trends in the prevalence of autism from these data. The committee concludes that this unpub- lished ecological analysis is uninformative with respect to causality. CAUSALITY ARGUMENT A number of case reports have been submitted through VAERS and directly to the committee asserting an association between exposure to thimerosal- containing vaccines and neurological outcomes, autism in particular. Case re- ports are very useful in hypothesis generation and identifying areas for investi- gation, but are rarely useful in establishing causality. The case reports reviewed by the committee are uninformative with respect to causality. There are no published epidemiological studies that examine the potential association between exposure to thimerosal-containing vaccines and neurode- velopmental disorders. Unpublished studies reviewed by the committee provide inconclusive evidence of a potential association between exposure to thimerosal- containing vaccines and certain neurological developmental disorders. Among the unpublished reports, only one an examination of the hypothesis using data from the VSD (Verstraeten, 2001) is from a controlled epidemiological study. The committee, like other experts convened by the CDC, has several concerns about this study. These include: the inexactness of the diagnoses and inconsis- tencies across clinicians, clinics, and study sites, variation in results between study sites, indicative of potential ascertainment or health-care-seeking bias, potential bias due to disenrollment, the small effect sizes, the inconsistent dura- tion of observation, insufficient power to detect less common diagnoses, lack of information on prenatal exposures to mercury, and lack of a consistent dose-

Next: Significance Assessment »
Immunization Safety Review: Thimerosal-Containing Vaccines and Neurodevelopmental Disorders Get This Book
×
Buy Paperback | $45.00 Buy Ebook | $35.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

In this report, the Immunization Safety Review committee examines the hypothesis of whether or not the use of vaccines containing the preservative thimerosal can cause neurodevelopmental disorders (NDDs), specifically autism, attention deficit/hyperactivity disorder (ADHD), and speech or language delay.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!