Table 2.

Results of multiple logistic regression analyses examining the impact of risk factors on the trend in regular smoking in adolescents

Year	Model 1: OR for year partially adjusted (95% CI)	Model 1+best friend smokes (95% CI)	Model 1+ exposure to smoking in home (95% CI)	Model 1+ parental smoking	Model 1+ sibling smoking	Model 1+all risk factors
2003	1
2006	0.62 (0.59 to 0.64)	0.83* (0.78 to 0.87)	0.58 (0.55 to 0.61)	0.60 (0.57 to 0.63)	0.61(0.58 to 0.64)	0.75* (0.71 to 0.79)
2007	0.56 (0.53 to 0.59)	0.78* (0.74 to 0.83)	0.54 (0.52 to 0.57)	0.55 (0.52 to 0.58)	0.56 (0.54 to 0.59)	0.72* (0.68 to 0.76)
2008	0.51 (0.48 to 0.53)	0.74* (0.70 to 0.79)	0.49 (0.47 to 0.52)	0.50 (0.48 to 0.53)	0.51 (0.48 to 0.53)	0.68* (0.64 to 0.72)
2009	0.47 (0.44 to 0.49)	0.69*(0.65 to 0.73)	0.46 (0.43 to 0.49)	0.46 (0.44 to 0.49)	0.47 (0.45 to 0.50)	0.63* (0.59 to 0.67)
2010	0.40 (0.38 to 0.42)	0.58*(0.54 to 0.61)	0.40 (0.38 to 0.42)	0.39 (0.37 to 0.41)	0.40 (0.38 to 0.42)	0.53* (0.50 to 0.57)
2011	0.36 (0.34 to 0.38)	0.55* (0.51 to 0.58)	0.33 (0.31 to 0.35)	0.36 (0.34 to 0.38)	0.37 (0.35 to 0.39)	0.47* (0.44 to 0.51)
2012	0.28 (0.27 to 0.30)	0.42* (0.39 to 0.45)	0.26 (0.25 to 0.28)	0.29 (0.27 to 0.30)	0.29 (0.27 to 0.31)	0.37* (0.35 to 0.40)
2013	0.27 (0.25 to 0.28)	0.41* (0.39 to 0.44)	0.28 (0.26 to 0.29)	0.27 (0.26 to 0.29)	0.28 (0.26 to 0.30)	0.39* (0.37 to 0.42)
2014	0.24 (0.22 to 0.25)	0.36* (0.34 to 0.39)	0.23 (0.22 to 0.25)	0.24 (0.23 to 0.26)	0.25 (0.24 to 0.27)	0.34* (0.32 to 0.36)
2015	0.21 (0.19 to 0.22)	0.34* (0.32 to 0.37)	0.20 (0.19 to 0.22)	0.21 (0.20to 0.23)	0.22 (0.21 to 0.24)	0.31* (0.29 to 0.34)
All years combined, using year as a continuous variable
Linear trend (2003–2015)	0.88 (0.88 to 0.88)	0.91* (0.91 to 0.92)	0.88 (0.88 to 0.88)	0.88 (0.88 to 0.89)	0.88(0.88 to 0.89)	0.91* (0.90 to 0.91)

Model 1 is adjusted for age, gender, ethnicity and school decile.

*OR >model 1 OR (p<0.05).