Descriptive data for the full sample and subsamples
| Cross-sectional sample (total N=2836) | Longitudinal sample of baseline never used cigarettes (total n=1726) | Longitudinal sample of baseline once/ used to use cigarettes (total n=318) | |||||
| N/M | (%/SD) | N/M | (%/SD) | N/M | (%/SD) | ||
| Age | 13.18 | (0.39) | 13.18 | (0.39) | 13.17 | (0.39) | |
| Sex | Boy | 1411 | (49.8%) | 898 | (48.0%) | 164 | (51.6%) |
| Girl | 1425 | (50.2%) | 898 | (52.0%) | 154 | (48.4%) | |
| Heard of e-cigarettes (baseline) | No | 346 | (12.2%) | 227 | (13.2%) | 24 | (7.5%) |
| Yes | 2383 | (84.2%) | 1381 | (80.0%) | 286 | (90.0%) | |
| Don’t know | 103 | (3.2%) | 118 | (6.8%) | 8 | (2.5%) | |
| Ever used e-cigarettes (baseline) | No | 1867 | (65.8%) | 1383 | (80.1%) | 70 | (22.0%) |
| Yes | 969 | (34.2%) | 343 | (19.9%) | 248 | (78.0%) | |
| Ever used cigarettes (baseline) | No | 2196 | (77.4%) | 1726) | (100.0% | 0 | (0.0%) |
| Yes | 640 | (22.6%) | 0 | (0.0%) | 318 | (100.0%) | |
| Family smokers = none | 898 | (31.7%) | 666 | (38.6%) | 42 | (13.2%) | |
| Family smokers = one | 852 | (30.0%) | 534 | (30.9%) | 88 | (27.7%) | |
| Family smokers = two | 517 | (19.2%) | 298 | (17.3%) | 74 | (23.2%) | |
| Family smokers = three or more | 569 | (20.1%) | 228 | (13.2%) | 114 | (35.8%) | |
| Friend smokers = none | 1384 | (48.8%) | 1050 | (60.8%) | 67 | (21.1%) | |
| Friend smokers = a few | 1135 | (40.0%) | 613 | (35.5%) | 189 | (59.4%) | |
| Friend smokers = most | 317 | (11.2%) | 63 | (3.7%) | 62 | (19.5%) | |
| Intentions | 4.69 | (0.77) | 4.87 | (0.50) | 4.48 | (0.76) | |
| Attitude | 4.73 | (0.57) | 4.88 | (0.32) | 4.51 | (0.65) | |
| Perceived norms | 4.81 | (0.57) | 4.91 | (0.30) | 4.66 | (0.50) | |
| Perceived behavioural control | 4.61 | (0.72) | 4.78 | (0.49) | 4.43 | (0.71) | |
| Self-efficacy | 4.64 | (0.77) | 4.83 | (0.47) | 4.41 | (0.82) | |
| Free school meals* | 14.24 | (6.63) | 13.82 | (6.55) | 15.57 | (6.35) | |
*Mean and SD for this variable based on school-level data.