The difference (Δ) in bronchial responsiveness (BR), expressed as doubling doses of methacholine^§, between the first FE_NO quartile (Q₁) and the other quartiles (Q₂–Q₄) in all subjects, atopics and non-atopics, after stratifying for smoking.

§ Slope was the outcome of the regression model and doubling doses were obtained by multiplying the regression coefficients with 1.66, as described in the Methods. * p-value for trend represents the statistical significance for the association between bronchial responsiveness and FENO quartile (used as a qualitative variable). #p-value for interaction represents the significance of interaction of smoking status with FENO quartile on airways responsiveness. All the coefficients and p-values are adjusted for gender, study centre, FEV1(%pred), age, height, weight, atopy, current asthma.§ 斜率（Slope）为回归模型的输出结果，加倍剂量的计算方式为将回归系数乘以1.66，具体如方法部分所述。 * 趋势检验p值代表支气管反应性与作为定性变量处理的呼出气一氧化氮（FENO）四分位组之间关联的统计学显著性。 # 交互作用p值代表吸烟状态与FENO四分位组对气道反应性的交互作用的统计学显著性。 所有系数与p值均已针对性别、研究中心、预测值一秒用力呼气容积（FEV1(%pred)）、年龄、身高、体重、特应性及当前哮喘状态进行了校正。