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Table 5 Mutually adjusted risk ratios (RRs)* for the association between CB and each potential predictor

From: Diverging trends of chronic bronchitis and smoking habits between 1998 and 2010

  RR [95% CI]  
  ISAYA (1998/2000) GEIRD (2007/2010) p-value for heterogeneity
Gender (female vs male) 1.17 [1.09−1.27] 1.11 [1.00−1.22] 0.721
Smoking habits (vs never smoking):    
 Past light smoking 1.40 [1.21−1.62] 1.03 [0.86−1.23] 0.015
 Past heavy smoking 2.47 [1.96−3.13] 1.66 [1.19−2.31] 0.151
 Current light smoking 2.15 [1.95−2.37] 1.95 [1.73−2.19] 0.144
 Current heavy smoking 4.82 [4.31−5.39] 3.57 [3.11−4.11] 0.018
Occupational status (unemployed/retired subject vs employed subject/house-person/student) 1.11 [0.97−1.28] 1.53 [1.31−1.79] 0.019
Asthma (present vs absent) 2.08 [1.84−2.34] 2.01 [1.77−2.30] 0.635
Allergic rhinitis (present vs absent) 1.76 [1.60−1.93] 1.81 [1.63−2.02] 0.680
  1. * RRs also adjusted for age, season of response, type of contact, cumulative response rate, and centre.
  2. p-value obtained by considering the data from both the studies in the model and by testing the null hypothesis that the regression coefficient of the interaction term between the covariate and the dummy indicator of the study (GEIRD vs ISAYA) was zero.