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Veterans and Agent Orange Health Effects of Herbicides Used in Vietnam (1994) / Chapter Skim
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C: Methodologic Observations on the Ranch Hand Study
Pages 757-763

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From page 757...
... The committee is aware of the logistical difficulties involved in such a large and detailed data collection effort, and it applauds the efforts of the Air Force research team in that regard. In addition, the committee also acknowledges the efforts of the Ranch Hands themselves to participate in the follow-up study; they deserve a great deal of appreciation for their efforts.
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From page 758...
... The executive summary, in particular, contains essentially none of the relevant quantitative data. Exploration of an Overall Effect A more specific concern involves the text on page i, describing overall differences between Ranch Hands and control groups.
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From page 759...
... For this reason, internal comparisons based on different exposure measurements among the Ranch Hands themselves are appealing. The use of multiple definitions of exposure (extrapolated baseline dioxin, current dioxin adjusted for time between SEA experience and dioxin assay, and categorized current dioxin)
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From page 760...
... Because of the high a priori likelihood that extrabinomial variation exists, however, methods that accommodate such variation should be used whenever they yield results different from those obtained by standard methods, which assume independence, even when the tests of that variation do not provide statistically significant results. The generalized estimating equation methods of Zeger and colleagues (Zeger and Liang, 1986; Zeger et al., 1988)
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From page 761...
... If, as seems possible, those who had the highest dioxin residues tended to enter SEA service earlier so that they had the chance for longer or repeat tours, the higher number of conceptions could be explained by the longer period since their return during which they were "at risk" for conception. It is standard practice in demography to take account of period at risk when analyzing fertility rates in different populations, and the same methods would be appropriate here.
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From page 762...
... The technical issues raised above, particularly the restriction to those with current dioxin levels above background and the potential misapplication and/or misinterpretation of interaction terms, are of concern because of the conclusions drawn from them. The problems with the analyses could lead to apparently inconsistent findings with regard to the estimated effect of dioxin on outcomes.
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From page 763...
... 1992. An Epidemiologic Investigation of Health Effects in Air Force Personnel Following Exposure to Herbicides.
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Key Terms

  • ranch hands
  • dioxin levels
  • main effect
  • dioxin level
  • hand study

  • interaction term
  • birth defects
  • interaction terms
  • sea experience
  • logistic regression

  • current dioxin
  • future analyses
  • overall differences
  • dioxin residues
  • increased risk

  • highly correlated
  • hands themselves
  • continuous dioxin
  • effect term
  • serum dioxin

  • regression models
  • exposure measurements
  • table reporting
  • analysis comparing
  • potential misapplication

  • information specific
  • unexposed individuals
  • continuous exposure
  • multiple definitions
  • performed using


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