Epidemiologic Investigation of Health Effects in Air Force Personnel ...

The inherent match for SEA experience controls for combat-induced physiologic,
psychophysiologic, and other related morbidity and mortality disorders.
Additionally, this inherent match may reflect the effects of alcohol consumption,
the use of chemoprophylactic and/or illicit drugs, and the acquisition
of tropical diseases associated with life in SEA. The comparisons of the
exposed (RANCH HAND) subjects and their selected sets of controls are detailed
in Appendix Table A-4. Only 4 of the ten categorical AFSC/case strata had
less than ten controls for each exposed subject. The group of Caucasian
pilots had a mean of only 9.5 controls per exposed subject, due to the extreme
ages of several individuals, and the strata of Black pilots and other Black
officers had means of 2.7 and 5.0 controls respectively. However, since there
were only seven black officers in the exposed group and only thirty controls,
high numbers of tight rnatchos could not be achieved. Black enlisted aircrewmembers
had a mean of 9.8 controls each.
(4) Computer Science and Statistical Petal 1s of the Matching Process
As described above, the matching for this project has been performed using
three variables: occupational category, race and age. Five occupational
categories (officer/pilot, officer/navigator, officer/other, enlisted/flight
engineer, and enlisted/other) have been used to reflect socioeconomic status
and aeronautical rating. The variable of race has been dichotomized into
black and non-black. Ten matched controls have been selected for each exposed
subject, regardless of current vital status. The computer method applied to
select the control subjects is an adaptation of a procedure studied by Raynor
and Kupper (Nearest Neighbor Matching on a Continuous Variable, Technical
Report, Department of Biostatistics, University of North Carolina, 1979). As
the first step, the RANu! HAND and control groups were partitioned into ten
strata using the categorical occupational and race variables. The Raynor and
Kupper matching procedure was then applied iteratively within each of the
strata to match for the continuous variable of age, given in months. The
Raynor-Kupper procedure involves the following steps:
STEP #1.
STEP #2.
matching.
The RANCH HAND cohort in a given strata is randomly permuted.
The first RANCH HAND subject in the permuted set is selected for
STEP #3. The closest available control is assigned to the selected RANCH
HAND subject using the absolute value of the difference between the months of
birth of the RANCH HAND and the control subjects. If the closest available
control is further than 60 months from the selected RANCH HAND subject, a
blank is assigned. Tied assignments are broken randomly.
STEP #4. Step #3 is repeated for all RANCH HAND subjects in the strata
proceeding down through the permuted set, until the entire RANCH HAND cohort
is exhausted.
STEP #5. Steps #1 through #4 are repeated ten times for each RANCH HAND
subject to construct a 1:10 study set. At the completion of the matching
activity, the RANCH HAND - Control study matrices for each of the ten occupation-race
strata can be diagrammatically represented as in Figure #1.
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