| Wave 1 |
| Cohort | Total | X1 | X2 | X3 | X4 | X5 | X6 | X7 | X8 | X9 | X10 |
| N | 504 | 15 | 30 | 62 | 47 | 13 | 34 | 119 | 104 | 54 | 26 |
| Mean Age (SD) | 13.4 (.7) | 12.6 (.4) | 11.7 (.3) | 13.4 (.3) | 13.4 (.3) | 12.2 (.4) | 12.8 (.3) | 14.0 (.4) | 13.1 (.3) | 14.3 (.3) | 13.2 (.3) |
| Year group | 7–9 | 7–8 | 7 | 8 | 8 | 7–8 | 8 | 9 | 8 | 9 | 8 |
| Gender (% Female) | 55% | 40% | 50% | 100% | 100% | 100% | 47% | 0% | 100% | 0% | 58% |
| Ethnicity (% Caucasian) | 75% | 60% | 87% | 68% | 72% | 69% | 59% | 86% | 69% | 76% | 85% |
| SES (Median, IQR) | 4 (2) | 4 (2) | 3 (2) | 4 (2) | 3 (2) | 4 (2) | 2 (2) | 4 (1) | 4 (2) | 4 (2) | 3 (2) |
| Wave 2 |
| Cohort | Total | X1 | X2 | X3 | X4 | X5 | X6 | X7 | X8 | X9 | X10 |
| N | 450 | 9 | 25 | 60 | 40 | 6 | 26 | 109 | 101 | 50 | 24 |
| Mean Age (SD) | 14.5 (.6) | 14.0 (.4) | 13.3 (.3) | 14.5 (.3) | 14.8 (.3) | 13.5 (.2) | 14.0 (.3) | 15.1 (.4) | 14.1 (.3) | 15.4 (.3) | 14.3 (.3) |
| Year group | 8–10 | 8–9 | 9 | 9 | 10 | 8–9 | 9 | 10 | 9 | 10 | 9 |
| Gender (% Female) | 56% | 56% | 52% | 100% | 100% | 100% | 42% | 0% | 100% | 0% | 58% |
| Ethnicity (% Caucasian) | 75% | 56% | 84% | 67% | 73% | 67% | 65% | 86% | 69% | 74% | 42% |
| SES (Median, IQR) | 4 (2) | 4 (2) | 3 (2) | 4 (2) | 3 (2) | 4 (2) | 2 (2) | 4 (1) | 4 (2) | 4 (2) | 3 (2) |
| Wave 3 |
| Cohort | Total | X1 | X2 | X3 | X4 | X5 | X6 | X7 | X8 | X9 | X10 |
| N | 411 | 8 | 22 | 62 | 37 | 12 | 12 | 92 | 92 | 50 | 24 |
| Mean Age (SD) | 15.7 (.6) | 15.3 (.4) | 14.8 (.3) | 15.9 (.3) | 15.8 (.3) | 14.5 (.4) | 15.0 (.3) | 16.0 (.4) | 15.4 (.3) | 16.1 (.3) | 15.3 (.3) |
| Year group | 9–11 | 10–11 | 10 | 11 | 11 | 9–10 | 11 | 11 | 11 | 11 | 10 |
| Gender (% Female) | 58% | 50% | 46% | 100% | 100% | 100% | 67% | 0% | 100% | 0% | 58% |
| Ethnicity (% Caucasian) | 76% | 63% | 86% | 68% | 73% | 75% | 75% | 85% | 70% | 74% | 88% |
| SES (Median, IQR) | 4 (2) | 4 (2) | 3 (2) | 4 (2) | 3(2) | 4 (2) | 2 (2) | 4 (1) | 4 (2) | 4 (2) | 3 (2) |
- Note: Update from the protocol paper (Booth et al., 2017); age has now been coded to two decimal places, and SES (Socio-Economic Status) is the median of both mother and father education level; SD Standard Deviation; IQR Interquartile Range; 11% attrition at Wave 2 and 19% attrition by Wave 3
