Table 2

Unadjusted and adjusted risk factors for incident smoking in year 7

Risk factorUnadjusted OR95% CIp (χ2 tests)Adjusted OR*95% CIp (likelihood ratio tests)
*Mutually adjusted for all other variables in the table, using robust standard errors to adjust for clustering by school.
†Tests for linear trend.
CI, confidence interval; OR, odds ratio.
Year of questionnaire completion
    711
    82.912.04 to 4.152.741.85 to 4.06
    93.702.61 to 5.243.572.42 to 5.27
    105.133.66 to 7.194.232.89 to 6.17
    114.413.12 to 6.24<0.0013.852.62 to 5.65<0.001
Sex
    Boy11
    Girl1.591.36 to 1.86<0.0011.571.31 to 1.88<0.001
Parental smoking
    Neither parent smokes11
    Only father or mother smokes1.541.29 to 1.861.351.09 to 1.66
    Both parents smoke2.452.00 to 3.00<0.0012.011.59 to 2.56<0.001
Sibling smoking
    Non-smoking sibling(s)11
    Smoking sibling(s)3.222.69 to 3.85<0.0012.271.85 to 2.78<0.001
    No siblings0.940.67 to 1.330.880.60 to 1.29
Peer smoking: quartiles of proportion of classmates who had smoked at the beginning of year 7 (range)
    Lowest (0–7.4%)11
    2 (7.7–13.0%)1.361.08 to 1.731.200.92 to 1.58
    3 (13.3–19.2%)1.551.22 to 1.961.421.08 to 1.87
    Highest (20.0–48.0%)1.481.17 to 1.870.002†1.451.11 to 1.890.023
Social deprivation: quartiles of Townsend Index (range)
    Least deprived (−6.51 to −3.13)11
    2 (−3.12 to −0.84)1.311.02 to 1.681.190.92 to 1.58
    3 (−0.82 to 1.55)1.401.10 to 1.801.110.86 to 1.45
    Most deprived (1.55 to 9.31)1.771.39 to 2.25<0.001†1.230.94 to 1.590.42