Longitudinal FAQs

Most of us are aware of what a survey is. You may have taken part in an online poll or agreed to talk to a market researcher in the street – you may have been asked about your views in the run up to an election or asked to give your thoughts on products after buying them. But what are longitudinal studies, how are they different from these types of surveys and why are they important to society? Here are a few useful FAQs.

What is a longitudinal study?

A longitudinal study provides data about the same individual at different points in time allowing the researcher to track change at the individual level. You could think of it as a photograph album rather than a single snapshot. It tells a story of people’s lives at a moment in time, but also over time, showing how individuals or families have changed. In fact, longitudinal studies can also be used to study change in the lives of organisations and institutions as well as individual people.

How is it different from repeated cross-sectional studies like opinion polls?

Change can also be studied using repeated cross-sectional studies collected from different samples (groups of people). These reveal how the population as a whole has changed, but they do not reveal the complex pattern of changes at the individual level which lead to these changes. For example, between one year and the next there may be little change in the unemployment rate, but it is likely in this situation that large numbers of people will have left unemployment, and similar numbers will have have become unemployed.

Are there different types of longitudinal study?

Yes there are – here are some examples

  • Individual level panel surveys, where samples of individuals are tracked and interviewed
  • Household panel surveys, where individuals are followed within the context of the households where they live, and information is normally collected about the whole household at each wave
  • Cohort studies, where samples from a particular age range are followed to explore their different trajectories as they age
  • Record linkage studies, administrative or census data are linked across time

Why is longitudinal research useful/important?

The development of longitudinal studies over the last decade has underpinned advances in social science method and in understanding of major social changes and policy interventions. These studies provide an understanding of social change, of the trajectories of individual life histories and of the dynamic processes that underlie social and economic life. Their fundamental role in social science and policy research is the core rationale for the continued investment in longitudinal studies in the UK.

Is this an area that the UK is well known for?

The UK has taken a particularly prominent role in the development of longitudinal studies, with its unique portfolio of birth cohort studies, the Office for National Statistics (ONS) Longitudinal Study of the Census and the British Household Panel Survey and Understanding Society.

What sorts of issues does it help us learn about?

In common with most western societies, the UK is undergoing considerable socio-economic change. We have an ageing population, increasing diversity of ethnic background and rising levels of instability in both working careers and family life. Longitudinal studies collect data about different times in individuals’ lives, and across generations, linking evidence from different points in the lives of parents and children. This capacity to follow individuals through time and observe how experiences and behaviour are influenced by the wider social and economic contexts in which they find themselves – and perhaps how they in turn influence those contexts – gives longitudinal studies a major role in understanding social change.

How does it help us learn about these issues?

Longitudinal research can address issues and support methods in ways that are not possible with traditional cross-sectional approaches. It is particularly valuable in a number of research areas:

  • When the focus is directly on change and the phenomena are themselves inherently longitudinal – for example, the dynamics of poverty, employment instability, social mobility and changing social attitudes
  • When investigating causal processes – for example, the effects of unemployment on mental health or of child poverty on later life chances
  • When controlling for the effects of unmeasured fixed differences between subjects
  • When studying social change and needing to separate out age, period and cohort effects
  • When establishing the effect of a ‘treatment’ by following an experimental or quasi-experimental design or comparing periods before and after the introduction of public policy

How has it helped?

The advantages afforded by longitudinal research have been exploited for a wide range of important research findings:

Disentangling the effects on children of school and family background in order to understand social mobility and the effectiveness of educational interventions – and to identify the key points for intervention Examining the effects of changing patterns of marriage, cohabitation and childbirth on the time children are likely to spend in lone parent families – and the effects on their later lives Understanding the defining characteristics of people who experience repeated spells of unemployment and poverty – and their ‘scarring’ effects, which make it difficult for people to find work and/or escape poverty in the future