Newfoundland, and Radium Hill) include smoking data and have allowed a more effective examination of the combined effects of exposure to smoking and radon progeny. Additional years of follow-up and addition of new studies have also increased the information available on the modifying effect of age at risk, time since exposure, and time since last exposure. Finally, the studies now available include a wide range of exposure rates and have increased the information available on the modifying effect of exposure rate both within individual cohorts and in analyses of combined data from several cohorts.

Not only have new data become available, but informative statistical analyses of the data have been conducted. In most cases, investigators have modeled the hazard (age-specific risk) as a function of exposure and other variables, and this has allowed rigorous examination of the modifying effects of time-related variables, age at exposure, exposure rate, and smoking. That approach is comparable with that used by the BEIR IV committee, and many of the reports have compared findings from the study being evaluated with those predicted by the BEIR IV model. Special analyses addressing the combined effects of smoking and radon have been conducted by Thomas and others (1994), Yao and others (1994), and Moolgavkar and others (1993).

Most important, a working group of principal investigators, under the sponsorship of the U.S. National Cancer Institute (NCI), has analyzed combined data from 11 miner cohorts, including all available cohorts having at least 40 lung-cancer deaths and estimates of each participant's exposure to radon progeny (Lubin and others 1994a, 1995a). These analyses included 2,700 lung-cancer deaths in 68,000 miners, compared with 360 lung-cancer deaths in 22,200 miners included in the BEIR IV committee's analyses. Recent additional analyses of these data have provided a more-detailed examination of exposure-rate effects (Lubin and others 1995b) and of the low-exposure miner data (Lubin and others 1997).

The risk model recommended in the current report is based on analyses of data from the 11 cohorts evaluated by NCI, although for some cohorts data have been updated or modified in other ways. Although the committee chose to conduct its own analyses of these data to develop its risk model, it drew heavily on the extensive results included in the NCI report and papers noted above, particularly for addressing the modifying effects of such variables as smoking, exposure rate, age at first exposure, and time since exposure.

The purposes of this appendix are to describe the characteristics of the epidemiologic studies that were used to develop the committee's risk model and to summarize and discuss results of published analyses of data from these studies, particularly the extensive analyses conducted by NCI. Emphasis is given to information and analyses that have become available since publication of the BEIR IV report. The appendix is limited to lung-cancer risks; analyses of the miner data that address other health end points are discussed in chapter 4.

This appendix begins by providing an overall description of the characteristics of each of the 11 cohorts included in the combined analyses noted above and



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