Table 2.

Descriptive statistics for white matter, treatment, and alcohol and marijuana involvement

	Mean	SD
Fractional anisotropy (N=32)
Prefrontal	0.348	0.023
Orbitofrontal	0.329	0.028
Parietal	0.363	0.034
Temporal	0.312	0.024
Corpus callosum	0.494	0.034
Age at regular alcohol use	14.8	1.5
Age at regular marijuana use	14.1	1.9
BL motivation to abstain from alc in the next 30 days	6.3	3.6
BL motivation to abstain from mj in the next 30 days	7.5	3.4
Number of treatment days attended prior to the scan	18.2	8.7
Number of days abstinent from alcohol prior to scan	81.0	154.3
Number of days abstinent from marijuana prior to scan	55.4	67.1
Days of alcohol use in the 30 days prior to scan	1.6	2.8
Days of marijuana use in the 30 days prior to scan	5.8	10.8
Alcohol frequency at 6-mo (n=26)	3.0	1.9
Marijuana frequency at 6-mo (n=26)	2.9	2.5
6-mo RAPI score (n=27)	7.2	9.2
6-mo RMPI score (n=26)	9.8	11.8
Total drinks at 6-months (n=31)	34.4	71.3

Notes: N=32 unless noted otherwise. SD=standard deviation, BL=baseline, alc=alcohol, mj=marijuana, 6-mo= 6-month follow-up, RAPI= Rutgers Alcohol Problem Index, RMPI=Rutgers Marijuana Problems Index, Total drinks at 6-months= Total number of drinks consumed in the 30 days prior to 6-month follow-up (some adolescents who missed 6-months provided this TLFB-based data at a later follow-up). Substance use frequency response categories are listed in a note to Table 2.