ORs (95% CI) for illegal drug use at 16 and 30 years by childhood mental ability scores at the age of 10 (tertiles 1: 40.96–93.60; 2: 93.61–106.64; 3: 106.65–150.92) in 3818 men and 4128 women
| Illegal drug | Adjustments | |||||||
| Men | Women | |||||||
| Unadjusted | Confounding* | Intermediary† | All‡ | Unadjusted | Confounding* | Intermediary† | All‡ | |
| OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | |
| At 16 years of age | ||||||||
| Cannabis | 2305 (60.4%) | 2681 (65.0%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 1.83 (1.07 to 3.16) | 1.81 (1.08 to 3.22) | 1.90 (1.10 to 3.28) | 1.93 (1.12 to 3.33) | 2.54 (1.50 to 4.33) | 2.56 (1.50 to 4.37) | 2.76 (1.62 to 4.71) | 2.77 (1.62 to 4.74) | |
| 2.72 (1.64 to 4.51) | 2.88 (1.73 to 4.79) | 2.92 (1.75 to 4.85) | 3.07 (1.84 to 5.13) | 4.14 (2.50 to 6.83) | 4.09 (2.46 to 6.82) | 4.65 (2.80 to 7.72) | 4.62 (2.76 to 7.74) | |
| Cocaine | 2300 (60.2%) | 2679 (64.9%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 2.49 (0.52 to 2.05) | 2.33 (0.48 to 11.32) | 2.56 (0.53 to 12.41) | 2.33 (0.48 to 11.32) | 0.85 (0.25 to 2.95) | 0.92 (0.26 to 3.25) | 0.96 (0.27 to 3.27) | 0.92 (0.26 to 3.25) | |
| 2.08 (0.44 to 9.84) | 1.79 (0.37 to 8.59) | 2.19 (0.46 to 10.43) | 1.79 (0.37 to 8.59) | 0.77 (0.22 to 2.66) | 0.84 (0.23 to 3.05) | 0.88 (0.25 to 3.12) | 0.84 (0.23 to 3.05) | |
| At 30 years of age | ||||||||
| Cannabis | 2465 (64.6%) | 2888 (70.0%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 1.44 (1.16 to 1.79) | 1.44 (1.16 to 1.79) | 1.57 (1.26 to 1.97) | 1.58 (1.26 to 1.98) | 1.90 (1.44 to 2.50) | 1.88 (1.43 to 2.48) | 1.94 (1.45 to 2.59) | 1.92 (1.44 to 2.57) | |
| 1.98 (1.61 to 2.45) | 2.00 (1.62 to 2.47) | 2.23 (1.76 to 2.82) | 2.25 (1.78 to 2.85) | 3.33 (2.55 to 4.35) | 3.34 (2.56 to 4.36) | 3.24 (2.40 to 4.38) | 3.25 (2.41 to 4.40) | |
| Cocaine | 3510 (91.9%) | 3929 (95.1%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 1.60 (1.15 to 2.23) | 1.61 (1.16 to 2.24) | 1.81 (1.28 to 2.54) | 1.82 (1.29 to 2.56) | 1.59 (0.93 to 2.71) | 1.59 (0.93 to 2.71) | 1.56 (0.90 to 2.70) | 1.55 (0.90 to 2.69) | |
| 1.83 (1.33 to 2.51) | 1.84 (1.34 to 2.53) | 2.32 (1.64 to 3.28) | 2.34 (1.65 to 3.32) | 3.95 (2.45 to 6.35) | 3.96 (2.46 to 6.38) | 3.42 (2.03 to 5.76) | 3.42 (2.03 to 5.76) | |
| Ecstasy | 3316 (86.9%) | 3845 (93.1%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 1.28 (0.91 to 1.79) | 1.28 (0.91 to 1.79) | 1.51 (1.07 to 2.15) | 1.52 (1.07 to 2.15) | 1.28 (0.91 to 1.79) | 1.28 (0.91 to 1.79) | 1.51 (1.07 to 2.15) | 1.52 (1.07 to 2.15) | |
| 1.13 (0.81 to 1.58) | 1.14 (0.81 to 1.58) | 1.56 (1.08 to 2.26) | 1.57 (1.08 to 2.27) | 1.13 (0.81 to 1.58) | 1.14 (0.81 to 1.58) | 1.56 (1.08 to 2.26) | 1.57 (1.08 to 2.27) | |
| Amphetamines | 3006 (94.4%) | 3606 (87.4%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 0.91 (0.52 to 1.61) | 0.91 (0.52 to 1.61) | 0.94 (0.52 to 1.68) | 0.93 (0.52 to 1.67) | 0.91 (0.52 to 1.61) | 0.91 (0.52 to 1.61) | 0.94 (0.52 to 1.68) | 0.93 (0.52 to 1.67) | |
| 1.88 (1.15 to 3.09) | 1.16 (1.13 to 3.13) | 1.92 (1.10 to 3.33) | 1.94 (1.12 to 3.37) | 1.88 (1.15 to 3.08) | 1.91 (1.16 to 3.13) | 1.92 (1.10 to 3.33) | 1.94 (1.12 to 3.37) | |
| Polydrug use | 3818 (100%) | 4128 (100%) | ||||||
| 1.0 (ref) | 1.0 (ref) | |||||||
| 1.50 (1.02 to 2.20) | 1.49 (1.02 to 2.19) | 1.79 (1.20 to 2.65) | 1.78 (1.20 to 2.65) | 1.77 (0.86 to 3.70) | 1.78 (0.85 to 3.70) | 1.77 (0.84 to 3.74) | 1.77 (0.84 to 3.73) | |
| 1.44 (0.99 to 2.10) | 1.46 (0.99 to 2.11) | 1.98 (1.31 to 2.99) | 1.99 (1.32 to 3.00) | 4.44 (2.30 to 8.56) | 4.45 (2.31 to 8.59) | 4.28 (2.11 to 8.66) | 4.27 (2.11 to 8.68) | |
↵* Confounding variables: mothers' and fathers' social class (assessed at 5 years).
↵† Intermediary variables at 16 years: significant psychological distress. At 30 years: significant psychological distress (at 16), social class, monthly income, level of education (assessed at 30 years).
↵‡ All: all confounding and intermediary variables.