Table 1.

Hierarchical regression with percent tobacco choice (drug-seeking) or number of puffs consumed (drug-taking) as the dependent variables

Dependent variable	Level	Level 2 predictor	R	R 2	R 2 change	F change	p
Percent tobacco choice	1	3 BIS scales	.20	.04	.04	1.28	.29
	2	Uptake	.52	.27	.23	26.46	.000*
		Craving	.46	.21	.17	18.55	.000*
Number of puffs consumed	1	3 BIS scales	.14	.02	.02	.55	.65
	2	Uptake	.27	.07	.05	4.92	.03*
		Craving	.34	.12	.10	9.54	.003*

The three BIS impulsivity scales were predictors in level 1 (ns.). The level 2 predictors were either cigarettes per week (uptake) or smoking urges factor 1 (craving), and these predictors increased the proportion of variance accounted for significantly over the BIS scales. df—level 1 = 3,86 and level 2 = 1,85