Harmonised fertility histories in four British longitudinal cohort studies

Background: Since World War II, Britain has witnessed significant societal changes, including in relation to fertility. Robust longitudinal and cross-cohort research requires data harmonisation to create comparable fertility measures to understand the predictors and consequences of these changes across generations. Objective: This paper describes newly created datasets on fertility histories that have been derived and harmonised across four longitudinal British studies of cohorts born between 1946 and 1990. The consistency with national statistics on fertility are examined. Methods: The birth cohorts are: National Survey of Health and Development, born in 1946; the 1958 National Child Development Study; the 1970 British Cohort Study; Next Steps, born in 1989/90. Results: The harmonised datasets include information on the cohort members’ biological children at each survey sweep during childbearing age, such as whether they have children and if so how many, age of eldest and youngest child, number of boys and girls, and children by a previous partner. Additional variables related to non-biological children have been derived where possible. The percentage of female cohort members who have had at least one live birth and the number of children show a good degree of consistency with national statistics on fertility. Contribution: The harmonised datasets are well placed to improve fertility research across several generations born in Britain between 1946 and 1990. The possibility of linking these data with other variables from these cohort studies facilitates cross-cohort examination of fertility as an outcome, as a predictor, or as a covariate.