Disposition of the Air Force Health Study (2006) / Chapter Skim
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5 Value of the AFHS Research Assets
5 Value of the AFHS Research Assets
Pages 101-121
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From page 101... ...
It also addresses privacy and security concerns related to the retention and maintenance of the AFHS data assets. SCIENTIFIC MERIT OF THE DATA ASSETS Based on the information contained in Chapters 2–4 and the additional details presented below, the committee has reached the following findings: The AFHS Data Assets Are Unique: No Other Epidemiologic Dataset on Vietnam Veterans Contains as Detailed Information Over as Long a Time Period Subjects in the AFHS morbidity study have undergone up to six cycles of detailed physical examinations and questionnaire data collection over a 20-year period.
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From page 102... ...
These hard copy records were duplicated and exist as part of AFHS data assets. In addition, questionnaires were administered eliciting information on education; employment; income; marital and fertility history; child and family health; health habits; recreation, leisure, and physical activities; toxic substances exposure; military experience; and wartime herbicide exposure.
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Most "occupational" cohorts have similar limitations and researchers have developed means of dealing with these issues in their work. The Data Collected by the AFHS Appear to Be of High Quality and the Specimens Appear to Be Well Preserved The committee did not perform a comprehensive review of all AFHS data and specimens.
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The interim letter report also offered several recommendations for documenting and organizing the data assets in a form and format that would facilitate easy access to their contents. Analysis of the AFHS Data Assets Has Contributed to the Literature Addressing the Health of Vietnam Veterans In Spring 2005, Institute of Medicine (IOM)
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of AFHS data and the application of earlier AFHS findings (Warner et al., 2005) have served to refine TCDD half-life estimates with respect to elapsed time since exposure as well as the influence of body fat, the handling of nondetects and truncation of extrapolated values.
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Results of this research have been submitted for publication; they were presented in draft form in a June 2005 meeting the Ranch Hand Advisory committee (Liu et al., 2005)
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FUTURE POTENTIAL OF THE DATA ASSETS The completion of the Cycle 6 physical examinations marked the end of major data gathering activities planned by the AFHS before the currently scheduled termination date of the study in 2006.6 However, investigators, contractors, and collaborators continue to analyze data and specimens and publish results. Since the beginning of 2005, the Cycle 6 final report has been released, four papers have been published in peer-reviewed journals (Ketchum and Michalek, 2005; Kingman et al., 2005; Pavuk et al., 2005a,b)
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From page 108... ...
Most analyses use either an exposure surrogate based on wartime occupation or a categorical variable based on a serum dioxin level measured -- at minimum -- some 16 years after the last exposure. 8Such analyses were proposed in a 2004 AFHS presentation before the Ranch Hand Advisory Committee (RHAC, 2004)
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From page 109... ...
These data offer a valuable opportunity to explore how trends in risk factors influence the development of various diseases. Only in recent years has adequate statistical software become available to handle this situation, creating the opportunity for a number of longitudinal analyses that would have been difficult to perform in earlier years.9 New Analyses Can Be Performed on the Existing Medical Records and Other Study Data That Examine Questions That Were Not Addressed in the AFHS AFHS analyses focused on the influence of herbicide or dioxin exposure on health outcomes.
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Other forms of study design such as nested case–cohort and case–control studies may be appropriate for such research. And in some of these studies, it may be desirable to limit the study group to only the Ranch Hands or only the comparison group.
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. Studies of biomarkers of response or susceptibility in relation to health endpoints studied in the AFHS are also possible.
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The latest AFHS mortality update (Ketchum and Michalek, 2005) reported an elevated relative risk for all-cause mortality among all Ranch Hand veterans and a statistically significant increase in the risk of death from circulatory system diseases among veterans with the highest serum dioxin levels.
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These calculations were made under the assumption that statistical bias was not present. Whether or not such bias will be an issue in any future analyses will depend on the outcome being examined and the characteristics of the population for whom data are available.14 The rough estimates presented in the appendix suggest that, even in analyses limited to the subjects who participated in one or more cycle exams, the AFHS cohort is large enough to detect moderate to large associations in future mortality analyses of health outcomes of potential interest to Vietnam veterans.
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(2002) describe one such mechanism that is in place for gathering data from participants in the Vietnam Era Twins Registry.
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and Chapters 3 and 4, the committee has concluded that the present state of the documentation and organization of the AFHS medical records, other study data, and laboratory specimens is an obstacle to retaining and maintaining these materials after the currently scheduled termination date of the study. Several recommendations intended to address these obstacles were offered.
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CONCLUSIONS AND OBSERVATIONS On the basis of its review of AFHS reports, its site visit to the study facility, the scientific literature, and other information presented in this and previous chapters, the committee has reached the following conclusion: There is scientific merit in retaining and maintaining the medical records, other study data, and laboratory specimens collected in the course of the Air Force Health Study after the study's currently scheduled termination date. Although it was not part of its evaluation of their scientific merit, the committee notes that the AFHS data assets were obtained at a considerable cost to the government and represent a substantial investment in time and dedication by the study's subjects.
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REFERENCES AFHS (Air Force Health Study)
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2005b. Disposition of the Air Force Health Study -- Interim Letter Report.
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2005. Air Force Health Study Update; June 10, 2005.
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1989. Estimates of the half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin in Vietnam veter ans of Operation Ranch Hand.
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1995. Paternal serum dioxin and reproductive outcomes among veterans of Operation Ranch Hand.
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