characterize the lung-cancer risk posed to the population by indoor radon, the two models for the exposure-risk relationship were applied to the distribution of exposures received by the population to estimate the burden of lung-cancer sustained by the population as a result of indoor-radon exposure. To characterize risks to the population, we have used the population attributable risk (AR), which indicates how much of the lung-cancer burden could, in theory, be prevented if all exposures to radon were reduced to the background level of radon in outdoor air. The AR estimates include cases in ever-smokers and never-smokers. To characterize the risk to specific individuals, the committee calculated the lifetime relative risk (LRR), which describes the relative increment in lung-cancer risk resulting from exposure to indoor radon beyond that from exposure to outdoor-background concentrations of radon.

Radon-Attributable Risks

LRRs were computed using the committee's risk models. Estimates were computed for exposure scenarios which reflect concentrations of indoor radon of interest. Table ES-1 shows the estimated LRRs for lifetime exposures at various constant radon concentrations. The LRR values are quite similar for the preferred 2 models: exposure-age-concentration and exposure-age-duration. The LRR values estimated by the BEIR VI models and the BEIR IV model are also similar, in spite of the addition of exposure rate to the new models. As anticipated, LRR values increase with exposure. Women have a somewhat steeper increment in LRR with increasing exposure because of differing mortality patterns.

Attributable risks for lung-cancer from indoor radon in the US population were computed with the committee's 2 preferred models and compared with the BEIR IV results. Based on the National Residential Radon Survey, the committee assumed a lognormal distribution for residential radon concentration, with a median of 24.3 Bqm-3 (0.67 pCiL-1) and a geometric standard deviation of 3.1 (Marcinowski 1994). The AR was calculated for the entire US population and for males and females and ever-smokers and never-smokers under the preferred submultiplicative model (Table ES-2). For the entire population, the ARs calculated with the new models ranged from about 10% to 14% and were higher than estimates based on the BEIR IV model. Under the submultiplicative assumption which was described on page ES-9, the attributable risk estimates for ever-smokers tended to be lower than estimates for never-smokers, although the numbers of cases are far greater in ever-smokers than in never-smokers.

These AR estimates for the general population are further broken down with respect to the distribution of indoor concentrations in Table ES-3. This analysis provides a picture of the potential consequences of alternative mitigation strategies that might be used for risk-management purposes. The findings were the same for the committee's 2 models. The radon concentration distribution is highly skewed, with homes with higher radon concentrations contributing dispro-



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