Case Report vs Case Series
A case report describes a single patient (or very few); a case series describes a group of patients with a shared feature, usually without a comparison group. Both are descriptive, so neither can establish causation or estimate risk, but a series can show patterns across several patients.
Comparison
| Feature | Case report | Case series |
|---|---|---|
| Number | One or a few | Several to many (often 5 or more) |
| Purpose | Illustrate a lesson, novelty | Describe features and course across patients |
| Detail | Deep detail per patient | Summary with tables, sometimes per-patient data |
| Methods | Narrative | Clear inclusion criteria and data collection |
| Evidence strength | Low | Low to modest; descriptive |
| Guidelines | CARE | Reporting guidance for series exists; check the EQUATOR Network for suitable options |
When to choose a series
- You have several similar patients and can define who is included.
- The question is "what is the typical course?" rather than "what happened to this patient?".
- You can describe how cases were identified, to limit selection bias.
What a series should contain
Inclusion criteria, how cases were found, data sources, a summary table, outcomes and a discussion of limitations. Ethics approval or exemption and consent requirements depend on local rules and journal policy.
Illustrative example
Invented for teaching. A department sees 11 patients with the same rare complication over three years. Rather than writing 11 case reports, it publishes a case series describing age, presentation, treatment and outcome, and states how cases were identified from records.
Practical advice
Decide early whether your material is a series or several separate reports, because journals treat them differently and a series needs a clear inclusion rule. State the period, the source of cases and the number excluded, if any. Describe each patient briefly in a table, protecting privacy, and focus the discussion on patterns across patients while acknowledging that a descriptive series has no comparison group.
Common pitfalls
- Selecting only striking cases.
- Calling a series a "cohort" or implying incidence.
Key takeaways
- Series describe patterns; reports illustrate lessons.
- Be transparent about how cases were identified.
References and further reading
- Gagnier JJ, Kienle G, Altman DG, et al. The CARE guidelines: consensus-based clinical case reporting guideline development. J Clin Epidemiol. 2014;67(1):46-51. doi:10.1016/j.jclinepi.2013.08.003
- Hulley SB, Cummings SR, Browner WS, Grady D, Newman TB. Designing Clinical Research. 4th ed. Lippincott Williams & Wilkins; 2013. Link
- EQUATOR Network: Enhancing the QUAlity and Transparency Of health Research (reporting guideline library). Link
Related reading
This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.