changes in the housing stock, from the time the study subjects lived in the dwellings until the time the measurements were carried out.
As a rule, the radon concentration decreases when a window is kept open. A window ajar can provide an exchange of 10 to 30 cubic meters of air per hour at a wind velocity of 3 m per second.47 This may be two to three times the normal rate of air exchange and thus may reduce the radon concentration by 50 to 70 percent.3,41 No data on sleeping near an open window were obtained at the time of radon measurements, however. There may have been a degree of exposure misclassification due to this factor.
We are indebted to the staff of the municipal public health boards for assistance with the radon measurements and to Georgina Bermann, Hillevi Giertz, Eva-Britt Gustafsson, Istvan Horwath, Gun Johnsson, Eva Juslin, Ann-Margret Lindevall, Inger Ostergren, Kristina Pannone, and Marianne Sigmond for valuable contributions in data collection and analysis.
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