The internet survey permitted us to tailor questions depending on answers to certain key questions. Thus, questions on their children were asked only for twins who indicated that they had children, items on nicotine dependence were asked only of smokers, and abstainers were not detailed alcohol items. As for the older cohort, the balance of questions was between retaining items from earlier questionnaires to permit longitudinal analyses and including items of relevance to these twins now in their mid-thirties. We asked them about their twin relationships, study and work, general health, symptoms, selected specific diseases and reading disorders. Seven items on weight and weight changes were included. Ten physical activity items were asked. Then they were asked about their partners, whether they had children and some details about each child and intentions to have more children. Alcohol use and alcohol-related problems, diet and tobacco use were assessed. A short personality scale was included before asking about satisfaction in various life domains. Waist circumference was recorded using the tape measure supplied in the invitation letter.
