Table 2.
Changes in Global Continuum of Illicit Drug Risk (GCIDR) and substance-specific ASSIST risk scores by condition.
| Model-Predicted Means | Statistical Tests | |||
|---|---|---|---|---|
|
| ||||
| IBI | CBI | Condition × Time Interaction | Time Main Effect | |
| Mean (SE) | Mean (SE) | (differential change for IBI vs. CBI) | (overall change) | |
| GCIDR (n= 359; 1,314 PTO) | Overall Test: χ2(3)= 5.64; p=.131 | χ2(3)=45.25; p<.001 | ||
| Baseline | 30.00 (1.27) | 33.11 (1.27) | ||
| 3 months | 28.75 (1.32) | 28.25 (1.30) | Baseline to 3m: χ2(1)=4.72 p= .030 | |
| 6 months | 27.36 (1.33) | 27.34 (1.30) | Baseline to 6m: χ2(1)= 3.51; p= .061 | |
| 12 months | 25.89 (1.34) | 26.51 (1.32) | Baseline to 12m: χ2(1)= 2.16; p= .141 | |
|
| ||||
| Marijuana (n= 314; 1,152 PTO) | Overall Test: χ2(3)= 7.79; p=.050 | χ2(3)=56.08; p<.001 | ||
| Baseline | 11.09 (0.49) | 11.03 (0.49) | ||
| 3 months | 11.08 (0.51) | 9.08 (0.50) | Baseline to 3m: χ2(1)=7.64 p= .006 | |
| 6 months | 9.52 (0.51) | 8.76 (0.50) | Baseline to 6m: χ2(1)= 0.99; p= .321 | |
| 12 months | 9.05 (0.52) | 8.10 (0.51) | Baseline to 12m: χ2(1)= 1.57; p= .210 | |
|
| ||||
| Cocaine (n= 66; 250 PTO) | Overall Test: χ2(3)= 10.35; p=.016 | χ2(3)=25.70; p<.001 | ||
| Baseline | 11.73 (2.01) | 10.35 (1.91) | ||
| 3 months | 10.85 (2.05) | 5.44 (1.93) | Baseline to 3m: χ2(1)= 4.54; p= .033 | |
| 6 months | 9.52 (2.05) | 4.22 (1.92) | Baseline to 6m: χ2(1)= 4.33; p= .037 | |
| 12 months | 7.30 (2.06) | 6.59 (1.92) | Baseline to 12m: χ2(1)= 0.12; p= .727 | |
|
| ||||
| Alcohol (n= 101; 367 PTO) | Overall Test: χ2(3)= 8.37; p=.039 | χ2(3)=61.68; p<.001 | ||
| Baseline | 16.13 (0.91) | 17.95 (1.10) | ||
| 3 months | 13.19 (0.94) | 11.08 (1.16) | Baseline to 3m: χ2(1)= 5.84; p= .016 | |
| 6 months | 12.63 (0.96) | 12.02 (1.15) | Baseline to 6m: χ2(1)= 2.23; p= .135 | |
| 12 months | 10.38 (0.98) | 12.26 (1.17) | Baseline to 12m: χ2(1)= 0.00; p= .967 | |
Notes: PTO= person-time observations. Substance-specific analyses are restricted to participants who were at moderate risk for the substance at baseline. Data are derived from generalized linear mixed models of ASSIST scores.