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Disposition of the Air Force Health Study
strategy to enroll comparison subjects. Specifically, a pool of 23,978 subjects comprising C-130 crewmembers who had served in the Southeast Asia theater but who were not involved in spray missions were identified and deemed to be an appropriate comparison group. The exposure period for the Ranch Hand subjects spanned from 1962 to 1971, and the pool subjects served during the same period. From the comparison pool, 1,241 subjects were chosen to be part of the original comparison group. Comparison subjects were matched to Ranch Hand subjects by age, race, and military occupation.
Most of the AFHS research is focused on the morbidity component of the study, where exceptionally detailed data gathering took place. The initial physical examination and surveying of these AFHS subjects (Cycle 1) was conducted in 1982 and subsequent cycles were conducted in 1985, 1987, 1992, 1997, and 2002.
The AFHS uses a rather complex terminology in its reports to designate the status of its subjects. Comparison subjects enrolled in the study at the beginning of Cycle 1 evaluations are referred to as original comparison subjects. Because some of the original comparison subjects were deemed to be ineligible subsequent to enrollment (when more detailed investigation showed that they did not meet the selection criteria),2 a second category of comparison subjects was established to indicate those comparison subjects that were shifted from the pool to replace ineligible subjects during Cycle 1. A third category is called replacement comparison subjects. Replacement comparison subjects are those subjects available for study inclusion from the individual-level pools of up to 10 comparison subjects. This replacement strategy was implemented to reduce the effect on study power of loss to follow-up on comparison subjects. If an original comparison subject did not participate in a particular cycle visit but participated in a later cycle, he was still designated as an original comparison. Cohort enumeration is discussed in detail in Chapter 2.
Subjects who participated in Cycle 1 were termed either partially or fully compliant, depending on whether they completed only the questionnaire3 required of all subjects or both the questionnaire and physical exam. Cycle 1 questionnaires were administered by Louis Harris and Associates, Inc. The National Opinion Research Center (NORC), under contract with Science Applications International Corporation (SAIC), administered questionnaires during Cycles 2–6. The physical examination was conducted by the Kelsey-Seybold Clinic in Houston,
During Cycle 1 it was discovered that 18 percent of the comparison population was ineligible for study inclusion (AFHS, 1984a).
A short telephone questionnaire was offered to those subjects that refused to participate in the questionnaire. Refusal subjects who completed this short telephone survey are another “compliance” class reported in the Cycle 1 report (AFHS, 1984a). If a Ranch Hand survived the war but died prior to Cycle 1, next of kin were contacted and—if they consented—were administered a proxy version of the participants’ baseline questionnaire.