Table 3.

Prediction of marijuana use by demand Indices for low, mid, and high grade marijuana from a marijuana purchase task.

	Grams/week of marijuana
	Low grade marijuana		Mid grade marijuana		High grade marijuana
Predictor	Δ R2	ß	Δ R2	ß	Δ R2	ß
Step 1:  Demographic Variables	.06***		.05***		.05**
Sexa		−.03		.01		.01
Age (years)		.15**		.15**		.13*
Ethnicityb		.11*		.10*		.13*
Level of educationc		−.15**		−.16**		.08
Age at first use of marijuana (years)		−.10*		−.09†		−.14**
Step 2: Demand Indices	.11***		.14***		.11***
Breakpoint		−.08		−.20**		−.24**
Intensity of demand		.19**		.19***		.26**
Omax		.24**		.31***		.18*
Pmax		−.07		−.01		.01
Elasticity of demand		−.04		−.03		.25***
Adjusted R2	.14		.18		.14

Notes. Simple average (i.e., observed) values for Intensity of demand, O_max, and P_max from the overparameterized model were used in analyses. Regression coefficients represent results from each step prior to entry of subsequent step. For low grade marijuana, O_max was square-root transformed and P_max was common log-transformed. For mid grade marijuana, O_max was square-root transformed. For high grade marijuana, O_max was square-root transformed and Intensity of demand was common log-transformed. For each grade of marijuana, the absolute value of Elasticity of demand was common log-transformed, then the result was multiplied by −1 to retain the variable’s original direction. All significance tests are two-tailed.

^aSex was coded 1 = male, 0 = female.

^bEthnicity was coded 1 = European American, 0 = non-European American/minority.

^cLevel of education was coded 1 = some high school, 2 = finished high school, 3 = Associate’s degree, 4 = some college, 5 = Bachelor’s degree, 6 = some graduate training, and 7 =advanced degree.

^†p < .10.

^*p < .05.

^**p < .01.

^***p < .001.