Longitudinal studies like Young Lives involve repeated observation of the same individuals over long periods of time. They are carried out in many social and human sciences to uncover trends across populations and lifespans, and to track life events through generations. They have long been used to inform social policymaking in the UK and other developed countries, and are increasingly also being used by policymakers in international development.
The power of longitudinal research lies in its capacity to illuminate patterns of change in the lives of selected groups of people. Making repeated, structured observations about the same group over time allows the removal of time-invariant individual differences, and the identification of short and long-term patterns of change.
Longitudinal research can be divided into cross-sectional studies which sample a cross-section of the population and survey it at regular intervals, and cohort studies, which track a group of people selected because they have experienced the same event (typically birth) during a specified time period.
Cohort studies have been particularly useful and important for understanding children and childhood across many disciplines and use a range of quantitative and qualitative methods. Importantly, they provide policymakers with information about social difference and how individual children’s outcomes differ according to factors like gender and class.
Young Lives is using a combination of quantitative methods – a regular survey of all 12,000 children and their primary caregivers – together with in-depth qualitative research with a sub-sample of the children in order to build up a broad-based understanding of child development and childhood in developing countries at the beginning of the twenty-first century.