reflection of the uncertainty in estimating the lung-cancer risks of radon exposures and especially for never-smokers at low levels of radon exposure.

Uncertainty Considerations

Quantitative estimates of the lung-cancer risk imposed by radon are subject to uncertainties—uncertainties that need to be understood in using the risk projections as a basis for making risk-management decisions (see Table ES-5). Broad categories of uncertainties can be identified, including uncertainties arising from the miner data used to derive the lung-cancer risk models and the models themselves, from the representation of the relationship between exposure and dose, from the exposure-distribution data, from the demographic and lung-cancer mortality data, and from the assumptions made in extending the committee's models from the exposures received by the miners to those received by the general population. The committee addressed those sources of uncertainty qualitatively and, to a certain extent, quantitatively.

TABLE ES-5 Sources of uncertainty in estimates of lifetime risk of lung-cancer mortality resulting from exposure to radon in homes

I Sources of uncertainty arising from the model relating lung-cancer risk to exposure

A Uncertainties in parameter estimates derived from miner data

1 Sampling variation in the underground miner data;

2 Errors and limitations in the underground miner data;

a) Errors in health-effects data including vital status and information on cause of death;

b) Errors in data on exposure to radon and radon progeny including estimated cumulative exposures, exposure rates and durations;

c) Limitations in data on other exposures including data on smoking and on other exposures such as arsenic.

B Uncertainties in application of the lung-cancer exposure-response model and in its application to residential exposure to the general U.S. population

1 Shape of the exposure/exposure rate response function for estimates at varying exposures and exposure rates;

2 Temporal expression of risks;

3 Dependence of risks on sex;

4 Dependence of risks on age at exposure;

5 Dependence risks on smoking status.

II Sources of uncertainty arising from differences in radon progeny dosimetry in mines and in homes

III Sources of uncertainty arising from estimating the exposure distribution for the U.S. population exposure distribution model

1 Estimate of the average radon concentration;

2 Estimate of the average equilibrium fraction;

3 Estimate of the average occupancy factor.

IV Sources of uncertainty in the demographic data used to calculate lifetime risk

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