• CROSSROADS employment as a radiological technician or a radiation worker in the nuclear power industry).

Therefore, while retaining as basic the participant vs. nonparticipant comparison, we attempted to develop more refined measures of radiation exposure. After providing a historical backdrop to the dosimetry issues, this chapter describes the approaches we considered, details about the validity of those options, and the decisions upon which we base our analyses.

The National Research Council's 1985 study (Robinette et al. 1985) used dose data provided by the Defense Nuclear Agency's (DNA) Nuclear Test Personnel Review program, which attempted to assign to each individual participant a valid estimate of the radiation dose he had received (DNA 1984). Therefore, the initial plans for the Medical Follow-up Agency (MFUA) study of CROSSROADS participants reported here included the use of these individual dose assignments.

Later, a committee of another MFUA nuclear test exposure project¹⁷ reviewed the DNA dosimetry estimating procedures and results and issued a letter report (IOM 1995), stating that the dosimetry estimates were not appropriate for dose response analyses used in epidemiologic studies. The CROSSROADS committee and staff, based on that letter report and their own judgment, decided not to use the individual dose data in this study. We set out to explore other exposure proxies, determining how they correlated with each other and with the DNA-assigned individual dose estimates.

We consider four broad ways in which to categorize exposure:

1. DNA-assigned doses,
2. participant status,
3. target ship boarding status, and
4. Engineering & Hull specialty status

Each of these adds intuitive interpretive possibilities to the analysis, while at the same time involving a wide range of validity and precision. We discuss each in turn, offering definitions, advantages, and both practical and theoretical drawbacks to use as a dose surrogate.