Mortality of Veteran Participants in the CROSSROADS Nuclear Test (1996) / Chapter Skim
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Findings and Discussion
Findings and Discussion
Pages 62-85
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assertion that Navy personnel assigned to Engineering & Hull occupational specialties may have been exposed to radiation via pipes carrying contaminated water (Appendix B) , we also examine, as hypothesis C, the association of Engineering & Hull status (as a radiation exposure measurement surrogate)
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BOARDER GRADIENT To test effect of boarding status (see Chapter 10) as a stronger radiation exposure surrogate than participant status alone, the model substitutes for the participant status variable two indicator variables creating a hypothesized gradient of radiation exposure: nonparticipant control (baseline)
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Model B attempts to measure a hypothesized exposure gradient, with boarding participants as the most likely to be exposed to radiation hazard, nonboarding participants as less likely to be so exposed, and nonparticipants (controls) as unexposed.
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We note that both nonmalignant respiratory disease and respiratory cancer showed elevated but not significant relative risks. In addition, ill-defined causes and prostate cancer showed significantly decreased mortality risks of 0.769 (0.636-0.930)
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. However, the risk to boarding participants is not significantly different from nonboarding participants (tested formally25 and most easily seen by the overlapping confidence intervals)
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and the Army (including Army Air Corps, Table 11-11~. Only Navy personnel had boarder or Engineering & Hull status assigned; we therefore consider only the basic participant versus control comparison for the other services.
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TABLE 11-11. Mortality Rate Ratios of Participants Relative to Controls (Army, including Army Air Corps, n = 6,482)
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We present them here for completeness. DISCUSSION Boarders Navy personnel who, according to records, boarded target ships during the CROSSROADS period following either or both detonations are the most clearly identifiable group of participants exposed to ionizing radiation on contaminated target ships.
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There were no statistically significant elevations of mortality from all causes, malignancies, or leukemias in the Engineering & Hull group of participants compared to the non-Engineering & Hull group. More important, comparisons 26In the model comparing the 9,000 boarders to the controls and nonboarding participants combined, Iymphosarcoma and reticulosarcoma and Hodgkir''s Disease were the only 2 of 44 causes of death tested to reach statistical significance at the 0.05 level.
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Of the eight rate ratios noted at the 40 percent increased or decreased risk thresholds, seven were elevated. If we eliminate the two "all participants" relative risks, considering them duplicative of the boarder and nonboarder data, we still have five elevations out of the six independent rate ratios considered.
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Neither time-sinceshot nor age-at-shot interacted with exposure variables (participant status, boarder status, Engineering & Hull assignment) to produce statistically significant or otherwise observable relationships.
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80 Cal _` *
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study in that it covers only one nuclear test series whose nuclear detonations were completed within one month, six years before the beginning of the British testing period. The CROSSROADS cohort on which we base our analysis and conclusions is entirely Navy, but is 73 percent larger than the all-service Darby study cohort.
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reported finding increased relative risk for all-cause mortality in a study of 8,554 U.S. Navy personnel who participated in the HARDTACK nuclear test in 1958.
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All inexact matches were declared as missing participants, leading to a missing rate of 7 percent. If we adjust the crude mortality rate based on our assumptions above (i.e., that the deaths for the 7 percent missing participants are actually in our mortality count)
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In summary, selection bias may have contributed to some degree to our finding of increased relative risk for all-cause mortality among CROSSROADS participants. Given the completeness of the participant roster and the lack of a concomitant increase in all-malignancy risk, however, it is unlikely that this bias accounts for all of the increase observed.
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Finally, can the contribution of a self-selection bias in the participant cohort be quantified? And, how best can we control for it in ongoing and future studies of atomic veterans?
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