The average of the measurements was 8.7 × 10-4 with a standard error of 1.0 × 10-4. With a modeled geometric mean ventilation of 1.07 air changes per hour, the transfer coefficient is calculated to have the same value as the measurements. However, if the committee uses the estimate of the geometric mean of the ventilation rate of 0.77, the resulting estimate of the transfer coefficient is 1.2 × 10-4. The committee feels that there are problems with both the measurements and the model results. Considering the problems with both the measurements of the transfer coefficient and the measurements that are the input values for the model, the committee recommends that the Environmental Protection Agency continue to use 1.0 × 10-4 as the best central estimate of the transfer coefficient, based on the available data.

Because of the uncertainty in the value of the ventilation rate and its distributional characteristics, the committee recommends assuming that the transfer coefficient is between 0.8 and 1.2 × 10-4. The committee is not assigning a specific uncertainty to the central estimate, but rather assumes that the central estimate has the highest likelihood of lying within that range.

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