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

LIVING
RANCH HAND
INDIVIDUAL
Figure 3.
SELECTION PROCEDURE FOR THE QUESTIONNAIRE,
PHYSICAL EXAMINATION, AND FOLLOW-UP STUDY
Randomly Selected
Mortality Controls
Ji^
CONTROL INDIVIDUALS
t - t
**
t Deceased
- Unwilling
* Volunteer
** Replacement Candidates
C. 0verview of Stat i st i ca1 Methodology
The design of the study is presented in schematic form in Figure 4.
R' refers to RANCH HAND personnel and C" refers to the collection of all possible
control individuals. As defined, P' and C" will contain individuals who
are deceased of noncombat causes. Combat deaths are excluded from R 1 and C".
Since C" is approximately 20 times larger than R 1 , a randomized subsample C'
and C" will be obtained. C 1 will be constructed from C" by computer selection
of the ten matched controls for each exposed study subject. As previously
noted, close matches will be nude for the variables of age, AFSC, and race.
The matched controls will form tan cohorts, Ci through C 10 , as shown in Figure
1. A 50% random sample from each of the matched control sets of 10 will be
selected for inclusion in the mortality assessment so that a group, C' is
obtained that consists of 5 matched controls for each exposed subject. These
controls will be designated as initial replacement candidates for the morbidity
and follow-up studies. The remaining individuals in the control set will
be additional replacement candidates in the event that replacement must occur
beyond the members of the mortality set (see Figure 3). C' will be constructed
without regard to whether the individual is currently living or dead
so that an assessment of noncombat mortality can be accomplished.
28