. 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 2. Cox proportional hazards model for time to first cigarette (n = 1,269).

	Hazard Ratio (95% CI)
Cannabis use^*	2.50 (1.99 - 3.15)
Alcohol use^*	2.42 (1.99 - 2.94)
Oppositional defiant disorder^*	1.69 (1.34 - 2.13)
Maternal alcohol dependence^*	1.37 (1.10 - 1.70)
Nicotine dependence risk group (based on paternal status)^a
Group 1: high genetic (G), high environmental (E)^*	1.22 (1.01 - 1.49)
Group 2: high G, low E	1.14 (0.80 - 1.62)
Group 3: moderate G, low E	1.05 (0.79 - 1.40)
Alcohol dependence risk group (based on paternal status)^a
Group 1: high G, high E	1.07 (0.87 - 1.33)
Group 2: high G, low E	1.12 (0.86 - 1.47)
Group 3: moderate G, low E	1.03 (0.79 - 1.35)
Maternal nicotine dependence (Fagerstrom proxy)	1.08 (1.02 - 1.16)
Maternal ND X risk period from 14-15 years of age ^b ^*	0.88 (0.79 - 0.98)

Hazard ratios relative to Group 4 (control)

Interaction term included in the model to adjust for violation of proportional hazard assumption for maternal nicotine dependence.

p <.05