Table 4

Linear regression with geometric mean cotinine concentration as outcome variable, adjusting for age, number of parents who smoke and interaction terms between year and family socioeconomic classification (SEC)* (model 1, n=3322) and year and family affluence scale (FAS) (model 2, n=4049)

Model 1
Variableβ95% CIWald test p value
Year (ref: 2006)2007−0.56(−0.73 to −0.38)<0.001
Family SEC (ref: SEC 1)SEC 20.32(0.17 to 0.47)<0.001
SEC 30.45(0.26 to 0.65)
SEC 40.82(0.60, 1.04)
Family SEC*year interaction (ref: SEC 1*2006)SEC 2*2007−0.05(−0.26 to 0.16)0.278
SEC 3*20070.17(−0.16 to 0.50)
SEC 4*20070.17(−0.13 to 0.46)
Model 2
Year (ref: 2006)2007−0.61(−0.77 to −0.45)<0.001
Family affluence scale (FAS) (ref: high FAS)Medium FAS0.15(0.01 to 0.29)<0.001
Low FAS0.41(0.27 to 0.55)
FAS*Year interaction (ref: High FAS*2006)Medium FAS*20070.03(−0.18 to 0.24)0.074
Low FAS*20070.23(0.01 to 0.46)
  • * Family socioeconomic classification: family SEC1=I professional occupations & II managerial and technical; SEC2=IIIN skilled non-manual & IIIM skilled manual; SEC3=IV partly skilled and V unskilled; SEC4=economically inactive.