Analyses should be conducted to evaluate how sensitive the estimated associations between exposure opportunity and health outcomes are to the uncertainty in the exposure opportunity metrics and to varying approaches to estimating herbicide exposure, possibly including alternative approaches to exposure assignment as discussed in Chapter 3.
Opportunities to conduct research using the exposure assessment model should be open to investigators beyond the VA system to allow for the benefits of engaging the broader research community and to enhance public acceptance and credibility.
In support of the recommended epidemiologic studies, VA should work with DoD and NARA to
facilitate health research uses of military records that are subject to access barriers arising from privacy laws, and
arrange for assistance from DoD and NARA staff with appropriate expertise to aid researchers in the location and interpretation of military records for health research uses.
From its review of the Stellman team’s model, the committee also identified two areas where it urges further investigation.
First, efforts should be made to improve and refine the Stellman team’s model by exploring alternative formulations of the proximity-based exposure metrics and by incorporating alternative or additional model parameters that account for more aspects of herbicide fate and transport in the environment. Further development of the model will require an assessment of the additional data needed and the availability of these data.
Second, the sensitivity of the Stellman team’s model’s results to changes in parameter values should be assessed systematically. The committee specifically urges attention to the effects of potential inaccuracies in the data on the location of herbicide application or troop presence. It is also important to investigate, especially with any attempt to add refinements to the existing model, the effect of assumptions on factors such as spray swath, the concentration of the TCDD contamination, primary and secondary drift, soil conditions, initial and remaining canopy, and photodegradation of sprayed herbicide. Although the committee concluded, based on the information it reviewed, that direct validation of the accuracy of exposure assignment is not feasible, it encourages efforts to quantify the degree of accuracy and incorporate those estimates into the sensitivity analysis.