Table 3.

Negative Binomial Regression Results Evaluating Drinking as a Function of Identification and Perceived Norms for the Typical Student on Campus

Predictor	B	B SE	IRR	Lower 95% IRR	Upper 95% IRR	t	d
Step 1: Δ-2LL = −19.29; df = 1; p < .001.
Campus	−0.317	0.051	0.728	0.659	0.805	−6.22***	0.21
Step 2: Δ-2LL = −128.76; df = 2; p < .001.
Identification	0.126	0.017	1.135	1.098	1.172	7.51***	0.25
Perceived Norm	0.045	0.003	1.046	1.039	1.052	13.91***	0.47
Step 3:Δ-2LL = −0.255, df = 1; p = ns.
Identification × Perceived Norm	0.002	0.002	1.002	0.997	1.006	0.73	0.02

Note.

^***p < .001. Δ-2LL at step 1 represents the change in −2 log likelihood relative to an intercept only model. IRR (incident rate ratio) represents proportional change for each unit increase in the predictor (e.g., an IRR of 1.05 = a 5% increase for each unit change in the predictor). Cohen’s d was calculated using the formula 2t(sqrt[df]). Campus was dummy coded (public campus = 0; private campus = 1).