Table 3.
Fit of trivariate probit regression model simultaneously to the three outcome variables of (1) dichotomized injection-drug-use subscale total, (2) four-category ordinal scale for sexual-behavior subscale total, and (3) non-response. Coefficient estimates are on scale of latent (unobserved) variables.
| Outcome variable | Explanatory variable | Coefficient estimate | SE | p-value |
|---|---|---|---|---|
| Injection-drug-use subscale total | Use last 30 days | 0.05952 | 0.1269 | 0.6392 |
| Age (years) | 0.02486 | 0.1254 | 0.8429 | |
| Individual therapy | −0.1329 | 0.1382 | 0.3364 | |
| White | 0.3385 | 0.1541 | 0.0283 | |
| African-American | 0.05124 | 0.1766 | 0.7718 | |
| Female | −0.03584 | 0.1215 | 0.7681 | |
| Days | 0.2208 | 0.06718 | 0.0011 | |
| Follow-up days (8) | −0.02579 | 0.2083 | 0.9015 | |
| Follow-up days (12) | −0.08676 | 0.07961 | 0.2760 | |
| Days × active | −0.09659 | 0.06685 | 0.1488 | |
| Follow-up days × active (8) | −0.1008 | 0.2156 | 0.6404 | |
| Follow-up days × active (12) | −0.02089 | 0.07949 | 0.7928 | |
| Shared random effect | 3.0516 | 0.2656 | <0.0001 | |
| Sexual-behavior subscale total | Use last 30 days | −0.00006 | 0.03384 | 0.9985 |
| Age (years) | −0.1183 | 0.03356 | 0.0004 | |
| Individual therapy | −0.1086 | 0.03751 | 0.0039 | |
| White | 0.002274 | 0.04083 | 0.9556 | |
| African-American | 0.06427 | 0.04653 | 0.1675 | |
| Female | 0.04399 | 0.03190 | 0.1683 | |
| Days | −0.1542 | 0.02683 | <0.0001 | |
| Follow-up days (8) | −0.01499 | 0.08431 | 0.8589 | |
| Follow-up days (12) | 0.009267 | 0.03043 | 0.7608 | |
| Days × active | 0.03357 | 0.02635 | 0.2029 | |
| Follow-up days × active (8) | 0.02448 | 0.08876 | 0.7828 | |
| Follow-up days × active (12) | −0.02892 | 0.03056 | 0.3443 | |
| Shared random effect | −0.5980 | 0.04111 | <0.0001 | |
| Non-response | Use last 30 days | −0.00088 | 0.05544 | 0.9874 |
| Age (years) | −0.2233 | 0.05523 | <0.0001 | |
| Individual therapy | 0.2975 | 0.06311 | <0.0001 | |
| White | 0.03650 | 0.06809 | 0.5920 | |
| African-American | −0.00269 | 0.07521 | 0.9715 | |
| Female | −0.04622 | 0.05249 | 0.3788 | |
| Active | −0.1006 | 0.04317 | 0.0200 | |
| Shared random effect | 1 | – | – |
Model terms are detailed in Methods. “Days × active” is difference in slopes over time for active minus placebo during the active-intervention period. “Follow-up Days × Active” is difference in the change in slopes from end of active-intervention period through follow-up for active minus placebo. Values in parentheses (8 or 12) refer to slope being allowed to differ over follow-up period depending upon length of active-intervention period. “Shared random-effect coefficient” is regression coefficient for shared random effect of that outcome. This coefficient was set to one for non-response outcome.