Results of proportional hazards regression analyses of five symptom groups on incident COPD events during follow up of subjects with normal and subjects with reduced forced expiratory volume in 1 s (FEV1)/vital capacity (VC).

Wald's Chi-squared+p-valueWald's Chi-squared+p-value
Subjects n54471
Nonproductive cough§3.680.0541.020.31
 N2-slope quintilesƒ10.900.0016.33<0.05
 Attained age##0.130.720.910.34
 Smoking habit score¶¶0.290.590.420.52
Productive cough§3.86<0.052.510.11
 N2-slope quintilesƒ11.710.00067.260.0071
 Attained age##0.130.720.890.35
 Smoking habit score¶¶0.380.540.510.48
 N2-slope quintilesƒ11.860.00065.910.0150
 Attained age##0.0020.971.280.26
 Smoking habit score¶¶0.410.520.170.68
 N2-slope quintilesƒ10.280.00137.580.0059
 Attained age##0.0030.960.080.78
 Smoking habit score¶¶0.620.430.300.58
Total symptom score++14.82<0.00016.580.0103
 N2-slope quintilesƒ10.260.00146.350.0117
 Attained age##0.060.811.660.20
 Smoking habit score¶¶0.060.810.340.56

p<0.05 was considered significant. #: FEV1/VC ≥lower limit of normal (LLN) according to Hedenström et al. [16]; : FEV1/VC <LLN according to Hedenström et al. [16]; +: expresses impact of exposures on outcome; §: represented by the sum of the questions involved; ƒ: alveolar slope of the single-breath nitrogen test in percentage of predicted normal according to Sixt et al. [17] in quintiles; ##: 50- or 60-year-old men in 1973; ¶¶: comprises five categories (never-smoker, ex-smoker, currently smoking 1–14 g·day−1, 15–24 g·day−1 and >24 g·day−1); ++: sum of yes-responses from all 12 symptoms.