Characteristics of the study participants at 7½ and 9½ years
| 7½ years (n=1258) | 9½ years (n=1045) | |
| Gender | ||
| Female | 33.2% | 32.8% |
| Male | 66.8% | 67.2% |
| n | 1258 | 1045 |
| Social class* | ||
| Non-manual (professional, managerial, skilled professions) | 82.0% | 82.3% |
| Manual (partly or unskilled occupations) | 18.0% | 17.7% |
| n | 1094 | 923 |
| Home ownership* | ||
| Owner/occupier | 85.5% | 87.5% |
| Rented accommodation | 14.5% | 12.5% |
| n | 1112 | 952 |
| Car access* | ||
| Yes | 91.1% | 91.8% |
| No | 8.9% | 8.2% |
| n | 1132 | 965 |
| Maternal education* | ||
| A-level or above | 43.9% | 46.9% |
| O-level | 33.6% | 33.4% |
| Certificate of secondary school/vocational/none | 22.5% | 19.7% |
| n | 1226 | 1021 |
*These variables were derived from responses to a questionnaire completed by mothers during the antenatal period.