In addition to the main surveys, which have aimed to collect information from all study members, there have been a number of ‘sub-studies’ that have sought to collect information from a smaller number of study members.
The 22 Month and 42 Month Surveys focused on exploring the impact of foetal nutrition on early development. Those invited to take part in the 22 Month Survey were 10 per cent of all study members, all twins and triplets, those born after more than 42 weeks of gestation and those who had particularly low birthweight. Around 2,500 took part. A similar number, though not the same people, took part in the 42 Month Survey.
Around 1,600 took part in the Age 21 Survey which involved an interview, two paper questionnaires and a set of literacy and numeracy assessments. The interview covered qualifications, training, current employment, unemployment, reading and writing behaviour, who you lived with, whether you had any children, where you lived, income and health.