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• Model A. BASIC
To test effect of participant status on mortality. Independent variables are:
participant status (1 = yes; 0 = no)
age on 1 July 1946 (continuous)
junior enlisted (baseline)
• Model B. 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)
nonboarding participant (level 1 exposure)
boarding participant (level 2 exposure)
• Model C. ENGINEERING & HULL
To test effect of the Engineering & Hull occupational category as a radiation exposure surrogate. Includes parameters of the basic model (A), less participant status—participants and controls are tested separately. A variable for Engineering & Hull status is added:
Engineering & Hull status (1 = yes, 0 = no)
Major mortality endpoints are: (1) all-cause, (2) all-malignancies, and (3) leukemias and aleukemias, excluding chronic lymphoid leukemia (CLL). Other descriptive mortality rates are presented by level of aggregation within cause of death (e.g., selected major categories, selected causes within selected major categories, etc.).
In developing the models displayed, we considered alternative modeling of variables, the role of other available data elements, and potential interactions among exposures and personnel characteristics. The tests that revealed no information are not displayed in these tables but are described later in this section.
In Tables 11-1 through 11-8 we display rate ratios calculated from estimated proportional hazards parameters for the first two models (A, participation effects, and B, boarding effects), using survival time as the response variable, censored as necessary at the end of the study follow-up period (31 December 1992). Results of Model C (Engineering & Hull effects) are presented separately in Tables 11-9. Because occupational specialty, of which the Engineering & Hull designation is one, is available only for enlisted personnel, we exclude officers from the analysis in Model C.