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Mean forced expiratory volume in 1 second (FEV1) values by age (and 95% confidence intervals [CI]) in male (black line) and female (gray line) healthy never smokers, expressed (A) in absolute values and (B) as percentage of the FEV1 value at the age of 25. The mean FEV1 decline value (and 95% CI) for males was 19.6 ml (17.1-22.1) and for females was 17.6 ml (13.8-21.4), with a p value of 0.266. (From Kohansal et al.32 Reprinted with permission of the American Thoracic Society.)
