Cox-proportional hazard analysis using age at onset of habitual smoking censored at non-habitual smokers.

1

Analysis was performed within family clusters using additive model. Age at interview in quartiles, gender, pc1, parental smoking and parental drinking were included as covariates.

2

Nominal P values are shown uncorrected for multiple testing. The Bonferroni-corrected significance threshold is P = 0.005.