Table 1.
Measures of association (polychoric correlations) between Parental Monitoring and Drug Initiation items along with twin pair (polychoric) correlations and 95% confidence intervals for each item.
| Items | Polychoric correlations | Twin Pair Correlations | ||||||
|---|---|---|---|---|---|---|---|---|
| 1. | 2. | 3. | 4. | 5. | 6. | MZ | DZ | |
| 1. Parents knowledge of child’s friends | 1.00 | 0.47 (0.37–0.56) | 0.39 (0.25–0.51) | |||||
| 2. Parents knowledge of how child spent their money | 0.74 | 1.00 | 0.45 (0.36–0.54) | 0.30 (0.15–0.43) | ||||
| 3. Parents knowledge of how child spent their free time | 0.72 | 0.82 | 1.00 | 0.47 (0.36–0.56) | 0.38 (0.24–0.51) | |||
| 4. Cannabis initiation | −0.24 | −0.31 | −0.34 | 1.00 | 0.81 (0.76–0.85) | 0.55 (0.45–0.64) | ||
| 5. Stimulants initiation | 0.27 | −0.32 | −0.31 | 0.76 | 1.00 | 0.66 (0.53–0.76) | 0.29 (0.10–0.47) | |
| 6. Cocaine initiation | −0.22 | −0.25 | −0.25 | 0.85 | 0.78 | 1.00 | 0.78 (0.68–0.85) | 0.45 (0.25–0.61) |
Note: All correlations adjusted for the effects of age at interview, sex and cohort on item thresholds