Longitudinal Single Case Study — Tracing Change in Depth Over Time
Longitudinal Single Case Study Design · Also known as: single-case longitudinal design, in-depth longitudinal case study, idiographic longitudinal study, LSCS
A longitudinal single case study is a qualitative research design that follows one bounded unit — a person, organization, program, or community — through multiple points in time. Unlike a cross-sectional snapshot, it captures how phenomena develop, shift, or respond to events across months or years, combining the contextual richness of case study methodology with the temporal depth needed to understand process and change.
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When to use it
Use a longitudinal single case study when the research question is inherently about process, trajectory, or change over time within a specific, bounded context — for example, how an organization adapts to crisis, how a patient navigates chronic illness, or how a policy unfolds during implementation. It is appropriate when access to one case in depth is possible but wide sampling is not, or when the case is theoretically extreme or revelatory. Do NOT use this design when the goal is statistical generalization across many units, when resources do not allow sustained engagement over time, when the case is too vague or unbounded to study systematically, or when cross-case comparison is the primary research aim — a multiple-case study would be more suitable in that circumstance.
Strengths & limitations
- Provides unmatched contextual depth and process-level understanding that large-n designs cannot offer.
- Captures temporal dynamics — how phenomena evolve, accelerate, reverse, or stall — rather than static states.
- Triangulation across multiple data sources (interviews, documents, observations) strengthens the credibility of interpretations.
- Enables analytical generalization: a well-chosen single case can generate or test theoretical propositions with broad applicability.
- Flexible enough to accommodate emergent findings; the protocol can be refined as the case reveals unexpected complexity.
- Findings are not statistically generalizable; the design supports analytical, not population, generalization.
- Longitudinal access requires sustained cooperation from participants and gate-keepers — attrition or access loss can compromise the study.
- Researcher presence over extended fieldwork may influence the case (observer effect), and repeated contact can create dependency or bias.
- Time- and resource-intensive: multi-year data collection and analysis demand a substantial commitment that limits feasibility for many projects.
Frequently asked
How is a longitudinal single case study different from a basic case study?
A basic case study can be conducted at a single point in time (cross-sectional). The longitudinal variant adds a planned temporal structure: data are collected across at least two — ideally three or more — waves separated by meaningful time intervals, so that change, process, and trajectory become observable. The epistemological logic is the same, but the longitudinal design answers different questions: not just 'what is happening here?' but 'how and why is it changing?'
How many time points do I need?
A minimum of two waves distinguishes a longitudinal from a purely cross-sectional design, but two points yield only a before-after comparison, not a process account. Three or more waves allow the analyst to identify turning points, non-linear change, and causal sequences. The optimal number depends on the expected pace of change in the phenomenon — fast-moving cases (a startup pivot) may need monthly check-ins; slow processes (organizational culture shift) may justify annual waves.
Can I use quantitative measures alongside qualitative data in a longitudinal single case study?
Yes. Case study methodology explicitly endorses mixed evidence: quantitative records (attendance rates, financial data, clinical scores) can be combined with qualitative interview data and field notes. The key is that the case — not the variable — remains the unit of analysis, and quantitative data serve to illuminate the case rather than to generalize across cases.
How do I handle participant attrition over the study period?
Attrition should be anticipated in the protocol. Strategies include recruiting a small redundant set of informants, maintaining contact between waves, and documenting who drops out and why — the pattern of attrition is itself potentially meaningful data. If a key informant leaves, the researcher must assess whether the remaining data still bound the case adequately or whether the design needs to be formally revised.
Is one case ever enough to publish?
Yes, if the case is theoretically motivated and the findings are framed as analytical rather than statistical generalizations. Landmark single-case longitudinal studies appear in top journals across organizational studies, education, clinical psychology, and sociology. The credibility requirement is rigorous triangulation, transparent methods, and clear theoretical contribution — not a large n.
Sources
- Yin, R. K. (2018). Case Study Research and Applications: Design and Methods (6th ed.). Sage. ISBN: 978-1506336169
- Gerring, J. (2007). Case Study Research: Principles and Practices. Cambridge University Press. ISBN: 978-0521676557
How to cite this page
ScholarGate. (2026, June 3). Longitudinal Single Case Study Design. ScholarGate. https://scholargate.app/en/qualitative/longitudinal-single-case-study
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Action ResearchQualitative Research↔ compare
- Case StudyQualitative↔ compare
- EthnographyQualitative↔ compare
- Multiple-Case StudyQualitative↔ compare
- Narrative AnalysisQualitative↔ compare
- Process TracingPsychometrics↔ compare