Descriptive statistics for study variables according to academic ability (unweighted)
| Study variables | Academic ability at age 11/12 | p Value | Total (N=6059) | ||
|---|---|---|---|---|---|
| Low (15.00–26.74) (N=2024, 33.40%) | Medium (26.75–29.89) (N=2023, 33.39%) | High (29.90–36.00) (N=2012, 33.21%) | |||
| Age, M (SD) | 14.21 (0.30) | 14.23 (0.31) | 14.28 (0.31) | <0.001 | 14.24 (0.31) |
| Female, N (%) | 1030 (50.89) | 1077 (53.24) | 986 (49.01) | 0.027 | 3093 (51.05) |
| Longstanding illness, disability or infirmity, N (%) | 299 (14.77) | 243 (12.01) | 221 (10.98) | 0.001 | 763 (12.59) |
| Ethnic minority*, N (%) | 748 (36.96) | 539 (26.64) | 438 (21.77) | <0.001 | 1725 (28.47) |
| Parental occupation (non-professional), N (%) | 1481 (73.17) | 1070 (52.89) | 737 (36.63) | <0.001 | 3288 (54.27) |
| Parental education (non-degree level), N (%) | 1875 (92.64) | 1709 (84.48) | 1382 (68.69) | <0.001 | 4966 (81.96) |
| Occasional early cigarette smoking age 14–16, N (%) | 157 (7.76) | 168 (8.30) | 162 (8.05) | 0.096 | 487 (8.04) |
| Persistent early cigarette smoking age 14–16, N (%) | 179 (8.84) | 181 (8.95) | 138 (6.86) | 0.096 | 498 (8.22) |
| Occasional early regular alcohol drinking age 14–17, N (%) | 702 (34.68) | 805 (39.79) | 801 (39.81) | <0.001 | 2308 (38.09) |
| Persistent early regular alcohol drinking age 14–17, N (%) | 375 (18.53) | 559 (27.63) | 640 (31.81) | <0.001 | 1574 (25.98) |
| Occasional early cannabis use age 14–17, N (%) | 361 (17.84) | 422 (20.86) | 401 (19.93) | <0.001 | 1184 (19.54) |
| Persistent early cannabis use age 14–17, N (%) | 197 (9.73) | 307 (15.18) | 283 (14.07) | <0.001 | 787 (12.99) |
| Occasional later regular alcohol drinking age 18–20, N (%) | 311 (15.37) | 211 (10.43) | 157 (7.80) | <0.001 | 679 (11.21) |
| Persistent later regular alcohol drinking age 18–20, N (%) | 1061 (52.42) | 1403 (69.35) | 1582 (78.63) | <0.001 | 4046 (66.78) |
| Occasional later cannabis use age 18–20, N (%) | 298 (14.72) | 393 (19.43) | 435 (21.62) | <0.001 | 1126 (18.58) |
| Persistent later cannabis use age 18–20, N (%) | 215 (10.62) | 351 (17.35) | 407 (20.23) | <0.001 | 973 (16.06) |
*Unweighted frequency (ethnic minority groups were oversampled).