. Author manuscript; available in PMC: 2009 Feb 1.

Published in final edited form as: Addict Behav. 2007 Sep 8;33(2):235–251. doi: 10.1016/j.addbeh.2007.09.002

Table 3. Cox proportional hazards model for transition time from first cigarette to onset of regular smoking (n = 817).

	Hazard Ratio (95% CI)
Cannabis use^*	2.38 (1.83 - 3.11)
Conduct disorder^*	1.64 (1.15 - 2.34)
Alcohol use^*	1.56 (1.12 - 2.18)
Age at first cigarette^a
Early (<= 13 years)^*	0.43 (0.25 - 0.73)
Late (>16 years)	0.76 (0.54 - 1.05)
Nicotine dependence risk group (based on paternal status)^b
Group 1: high G, high E^*	1.66 (1.20 - 2.29)
Group 2: high G, low E	1.62 (1.00 - 2.61)
Group 3: moderate G, low E	1.36 (0.89 - 2.10)
Maternal nicotine dependence (Fagerstrom proxy)	1.05 (0.97 - 1.13)
Alcohol dependence risk group (based on paternal status)^b
Group 1: high G, high E	0.81 (0.61 - 1.07)
Group 2: high G, low E	0.96 (0.66 - 1.41)
Group 3: moderate G, low E	0.91 (0.62 - 1.35)
Early first cigarette X risk period up to 1 year after first cigarette^c ^*	2.68 (1.40 - 5.13)
Early first cigarette X risk period 2-3 years after first cigarette^c ^*	6.51 (3.17 - 13.32)

Hazard ratios relative to median age at first cigarette (14-15 years)

Hazard ratios relative to Group 4 (control)

Interaction terms included in the model to adjust for violation of proportional hazard assumption for alcohol use and for early age at first cigarette.

p <.05