Assessing Health Outcomes Among Veterans of Project SHAD (Shipboard Hazard and Defense) (2016) / Chapter Skim
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Appendix D: Additional Information on Data and Methods Used for Analysis
Appendix D: Additional Information on Data and Methods Used for Analysis
Pages 151-164
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From page 151... ...
tests in exposure to test substances and potential exposure modifiers; and the selection of comparison groups to be used in the analyses of health outcomes in populations of special interest. Additional detail on the study's analyses addresses the selection of analyses to perform; Kaplan-Meier and Cox regression models for survival data, including consideration of competing risks and ship-clustering in analyses of specific causes of death; and correction for multiple comparisons.
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From page 152... ...
Requests were also submitted to Alabama, Arizona, the District of Columbia, Massachusetts, Nevada, the Philippines, and Rhode Island; but the requested death certificates were not located. The procedures to obtain access to 1 These data were supplied by the Health Statistics Section of the Colorado Department of Public Health and Environment, which specifically disclaims responsibility for any analyses, interpretations, or conclusions it has not provided.
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From page 153... ...
One approach was hypothesisdriven and the other was considered exploratory. Hypothesis-Driven Selection of Health Outcomes As described in the main body of the report and in Appendix C, the committee undertook a review of recent literature to identify adverse health outcomes that might be associated with exposure to substances used in the SHAD tests.
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From page 154... ...
Lung cancer a Because the individuals who served on the vessels involved in testing staphylococcal enterotoxin type B were not identified, the committee could not test the hypotheses generated for this agent. REPRESENTATION OF POTENTIAL EXPOSURE LEVELS As described in Chapter 3, the committee considered exposure in terms of the substances used in SHAD tests and number of times each SHAD participant had the potential to be exposed to a substance.
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From page 155... ...
. With this distribut tion, two gro oups are form lower (1-5 med: exposure opportunities n = 222)
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From page 156... ...
. Exposure opportunities are releases of the test substances o or e o s on over the ship or unit.
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From page 157... ...
To allow for the special features of their SHAD experiences, the committee examined the health outcomes for the crew of the USS George Eastman and the light tug boats and other Project SHAD technical staff (PSTS) , including the laboratory staff on the USS Granville S
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From page 158... ...
was included as an explanatory variable for analyses of the overall study population and the analysis of TOF exposure, which included a larger proportion of Marine participants. Because of the large amount of missing data on the race of the SHAD participants and comparison population and the lack of a feasible way to impute the missing data, the committee decided not to include race in the analysis.
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From page 159... ...
The committee carried out exploratory analyses involving multiple exposure groups among the SHAD participants that were created using the data grouping described in the previous section. The committee used Cox regression models to explore potential dose-response relationships between exposure level and mortality in conjunction with other factors such as age and enlisted status.
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From page 160... ...
The Holm's correction divides the sequence of m, m–1, …, into the 5 percent nominal level to form adjusted nominal levels of significance for the tests ascending from the smallest to largest p-value; tests with a p-value less than their respective adjusted significance level are significant. Because the multiple tests in the analysis of SHAD data, in particular those involving the same exposure and comparison groups, are less likely to be independent and because the adjustment to control FWER could compromise the ability to report a true significant test, the committee adopted the false discovery rate (FDR)
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From page 161... ...
Neither data from the SHAD I report nor data from the SHAD II analysis revealed significant differences between the exposed and comparison groups with respect to demographics and risk factors such as Vietnam experience or life style factors. Further, with the exception of specially outfitted ships such as the USS George Eastman, the USS Granville S
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From page 162... ...
Quantitative Exposure Metrics Quantitative exposure metrics were planned and explored in this study to capture varying degrees of exposure among the SHAD participants to provide an additional dimension for exploring whether an underlying exposure-response relationship exists. The metrics comprise three factors: the types of test agents used in the SHAD tests, the number of trials a person participated in and the number of exposure opportunities he had, and his assigned position (or bin)
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From page 163... ...
The quantitative exposure metrics were planned for use in analyses of both mortality and morbidity. However, because of study circumstances, the use of quantitative exposure metrics described in this section, including the analysis of the possible impact of location on the ship, was not carried out.
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