Multivariate proportional hazards regression of total symptom score, forced expiratory volume in 1 s (FEV1), N2-slope, attained age and smoking habit score on admission to hospital or death related to COPD

Parameter estimateWald's Chi-squared#p-valueHazard ratio (95% CI)
Total symptom score0.2020.7<0.00011.22 (1.12–1.33)
FEV1 (quintiles)+−0.355.6<0.050.71 (0.53–0.94)
N2-slope (quintiles)§0.499.5<0.0051.63 (1.20–2.22)
Attained ageƒ0.020.5ns1.02 (0.96–1.08)
Smoking habit score##0.030.1ns1.04 (0.79–1.37)

ns: nonsignificant. #: expresses impact of exposures on outcome with one degree of freedom for all variables; : sum of yes-responses from all 12 symptoms; +: FEV1 in percentage of predicted normal according to Hedenström et al. [16] in quintiles; §: alveolar slope of the single-breath nitrogen test in percentage of predicted normal according to Sixt et al. [17] in quintiles; ƒ: age at each year of follow-up; ##: 1=never-smoker, 2=ex-smoker since >6 months, 3=currently smoking 1–14 g·day−1, 4=smoking 15–24 g·day−1, 5=smoking >24 g·day−1.