Mixed methods in longitudinal research

1. Mixed methods in longitudinal research Nick Buck UK Longitudinal Studies Centre University of Essex

2. Overview • This presentation comes from quantitative survey perspective, • But main aim not to ask how qualitative methods could supplement research with quantitative motivation • Rather the aim is to consider in more general terms the rationales for longitudinal research, and consider how far they should motivate mixed methods research • This may involve use of language from quantitative research which is considered inappropriate in qualitative context, but perhaps there are analogues? • Distinguish full and partial longitudinal mixed methods, on basis of whether use longitudinal approach with all methods or only one

3. Why longitudinal research? • Longitudinal research defined here as using information collected from the same subjects at more than one point in time (i.e. not including retrospective life-history research based on single interview) • LR is normally more expensive, complex and time consuming than research based on single observations, both in data collection and analysis stages (if separable) • So requires special justification • At its simplest, rationale is requirement for information on change or stability at the level of the individual subject (NB not necessarily social change)

4. Analysis of individual level change • In quantitative LR concern is with change/stability of circumstances, behaviour, attitudes, values etc. • It is recognized that there is a measurement problem because of distance between survey response and ‘real’ behaviour etc (and also theoretical construct). • Issues of reliability and validity are more salient in LR because more obvious than in cross-sectional research. • For full longitudinal mixed methods need to raise the question whether there are analogues for these issues in qualitative LR, and what where the focus on change/stability lies in qualitative LR.

5. Quantitative LR focuses on: • Phenomena which are themselves inherently longitudinal, (eg poverty dynamics, employment instability, social mobility, social attitude stability); • Investigating causal processes, (e.g. impacts of unemployment on mental health or of child poverty on later life chances); • Controlling for the effects of unmeasured fixed differences between subjects; • The study of social change, separating out age, period and cohort effects; • Establishing the effect of a “treatment” in an experimental or quasi-experimental design, or comparing periods before and after the introduction of public policy.

6. Scope for mixed methods • Inherently longitudinal phenomena – clear scope for full and partial methods • Causal processes: partial methods? Understanding process in more detail • Controlling for unobservables: limited scope? Plausibility of assumptions? • Age, period and cohort: relies on large scale, long duration studies therefore limited scope? • Policy effects: similar to 1 ? • Other rationale coming from qualitative LR?

7. Types of longitudinal mixed methods: partial approaches • Longitudinal survey as sampling frame for qualitative study (selection of subjects on basis of life history) • LS as context for qualitative study (generalising on regularity of experiences – less straightforward than with cross-sectional data) • Qualitative study as supplement for empirical enrichment (understanding motivations for transitions) or conceptual development (e.g. social capital)

8. Types of mixed method longitudinal: full or parallel approaches • Quantitative data collection as part of ongoing ethnographic study • Qualitative components to LS (e.g. collection of verbatim responses to more open questions, vignettes) • Repeated observation on same individuals using survey and qualitative methods: presents considerable opportunities and challenges?