Longitudinal Research

Conceptual Overview and Discussion

Longitudinal research has been used in both experimental and case study designs: to evaluate the effectiveness of an intervention or theory; to assess the validity and reliability of a previous a single, short–time frame study; to identify factors that may constrain or support the long-term effectiveness of a strategy or initiative. Robert Yin has posited that comparative longitudinal case studies have such aims and, as such, are experimental. Other experimental researchers in education have used series of pretests and posttests administered around an intervention to different groups, so that results can be compared and contrasted. David Scott and Robin Usher point out, though, that the complexity of social factors impinging on what is happening—for example, within classroom learning environments—makes it difficult to determine precisely the full implications of an intervention by time sequenced testing alone.

A strength of longitudinal case study designs is that they enable a researcher to dig deeper into such complexities by using a range of methods over time, such as repeat interviews and observations, study of documents, and small-scale questionnaires. Such ongoing interactions with participants help to build participant–researcher trust, respect, and collaboration, and this in turn increases the possibility that rich, in-depth data will be generated for analysis. Critics of these kinds of researcher–participant relationships have warned that there is a potential here for bias—a researcher may be “captured” or overly swayed by a participant's subjective views of events, or vice versa. As Anne Oakley points out, however, personal engagement in research processes is more than dangerous bias; it is the condition under which people admit others into their lives.

All qualitative research involves interactions with people as they go about their daily lives. This requires researcher flexibility, as Michael Patton notes, but the need for flexibility may be greater in longitudinal case studies. Longer time spent in field work provides more opportunities for researchers to uncover unforeseen issues or debates, and these may require reconsiderations of previous assumptions or theoretical orientations and/or shifts in the research focus. Happily, more time is available also for adjustments to be made to the [Page 536]research design and questions. In such situations, however, researchers need to keep communication open and honest, ensuring that ethically appropriate agreements are reached about any changes to the original contract with participants and funders (if the latter are involved).

Engaging in early and ongoing inductive analysis in longitudinal research assists not only the management of large amounts of data collected but also, more significantly, in the building of robust interpretations, because there is time to reflect on data as they are generated and to further explore emerging findings in follow-up interviews and site visits. Often, a theme or grounded theory approach to analysis is used, but narrative analysis is also useful in enabling concurrent reporting and interpretation of chronological developments.

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