Table 4.
Unadjusted and adjusted conditional logistic regression results: likelihood (ORs and 95% CIs) of the at-risk twin (based on substance use history) having lower educational attainment than his cotwin.a
| Predictor | Number of Discordant Pairs |
Unadjusted Conditional Odds ratio |
Adjusted Conditional Odds ratio1 |
|---|---|---|---|
| Early Drinker | n=889 |
1.47 (1.05 – 2.05) |
1.44 (1.02 – 2.05) |
| Daily Nicotine Use b | n=702 |
2.42 (1.50 – 3.89) |
2.54 (1.55 – 4.17) |
| Early Cannabis Use | n=276 | 1.32 (0.76 – 2.29) |
1.35 (0.76 – 2.41) |
| Cannabis Initiation | n=947 | 0.86 (0.64 – 1.16) |
0.90 (0.65 – 1.24) |
| Alcohol Dependence | n=1023 |
1.67 (1.24 – 2.25) |
1.76 (1.27 – 2.44) |
| Nicotine Dependence | n=1059 |
1.34 (1.00 – 1.80) |
1.31 (0.98 – 1.77) |
| Cannabis Dependence | n=282 | 0.93 (0.56 – 1.56) |
0.93 (0.48 – 1.78) |
| Any illicit drug dependence | n=379 | 1.39 (0.89 – 2.18) |
1.23 (0.72 – 2.09) |
All adjusted models included four covariates: depression (DEPR), conduct disorder (CD), Southeast Asia service (SEA), and post-traumatic stress disorder (PTSD); no covariates were significant at p < .05.
The only significant interaction between zygosity and risk behavior was for daily nicotine use in the adjusted model (p=0.04; all others p > 0.20), conditional logistic regression analyses were collapsed across zygosity for all measures except daily nicotine use (for which the interaction was retained in both the unadjusted and adjusted models);
interaction OR=0.51 (0.25–1.04) in the unadjusted model and 0.46 (0.22–0.97) in the adjusted model