CPH Focus: Evidence-Based Approaches to Public Health: Epidemiology – Study Designs: Descriptive Studies (Case Reports, Case Series)
In this tutorial, we will focus on the concept of descriptive studies, specifically case reports and case series. Descriptive studies are often the first step in understanding health issues in a population, and they provide valuable information about emerging diseases and health trends. Understanding these study designs is essential for the Certified in Public Health (CPH) exam.
By the end of this tutorial, you’ll know what case reports and case series are, how they differ, and when they are used in public health research. As always, we’ll include practice questions to reinforce the concepts covered.
Table of Contents:
- Introduction to Descriptive Studies
- What Are Case Reports?
- Characteristics of Case Reports
- When to Use Case Reports
- What Are Case Series?
- Characteristics of Case Series
- When to Use Case Series
- Differences Between Case Reports and Case Series
- Limitations of Descriptive Studies
- Importance of Descriptive Studies in Public Health
- Practice Questions
- Conclusion
1. Introduction to Descriptive Studies
Descriptive studies are used in epidemiology to summarize the distribution of health-related events in terms of person, place, and time. They provide the foundation for forming hypotheses about the causes and risk factors of diseases. Unlike analytical studies, descriptive studies do not aim to determine causality but rather to describe occurrences or patterns.
The two main types of descriptive studies we will focus on are case reports and case series. Both study designs are valuable tools for documenting new or unusual cases and identifying potential public health concerns.
2. What Are Case Reports?
A case report is a detailed description of a single individual’s medical history, symptoms, diagnosis, treatment, and outcome. It provides valuable information about rare or novel conditions and can be used to alert the medical community to potential new diseases or unusual presentations of existing conditions.
2.1 Characteristics of Case Reports
Some key features of case reports include:
- Focus on a single patient or a small number of patients.
- Detailed documentation of clinical features such as symptoms, signs, laboratory findings, and outcomes.
- Often used to report rare or previously unknown conditions.
2.2 When to Use Case Reports
Case reports are useful when:
- A new or rare disease is identified.
- An existing disease presents in an unusual way.
- New side effects or complications of treatments are observed.
Though case reports cannot establish causality, they play an important role in generating hypotheses and guiding future research.
3. What Are Case Series?
A case series is a descriptive study that tracks several patients with a similar diagnosis or treatment over a period. Unlike case reports, which focus on one patient, case series examine multiple cases to identify trends, commonalities, and potential risk factors.
3.1 Characteristics of Case Series
Key characteristics of case series include:
- Involve more than one case but fewer patients than large observational studies.
- Describe common characteristics such as demographics, clinical presentations, and outcomes across multiple patients.
- Often the next step after case reports for further investigation.
3.2 When to Use Case Series
Case series are useful when:
- There is a need to explore patterns among multiple cases with the same diagnosis or exposure.
- Researchers aim to identify early trends that warrant further study through more rigorous research methods.
- There is a focus on understanding the natural history of a disease or treatment effects in a specific group.
4. Differences Between Case Reports and Case Series
While both case reports and case series describe health events, they differ in scope and purpose:
- Case Reports focus on a single patient or a very small group and provide detailed clinical documentation.
- Case Series examine a group of patients with similar characteristics and aim to identify trends or commonalities.
| Feature | Case Reports | Case Series |
|---|---|---|
| Number of Patients | Single or very few | Several patients |
| Purpose | Highlight new or rare conditions | Identify trends or commonalities among similar cases |
| Level of Detail | Highly detailed, focusing on one case | Describes characteristics across a group |
5. Limitations of Descriptive Studies
While case reports and case series provide valuable insights, they also have limitations:
- They cannot establish causality or determine risk factors because they lack a comparison group.
- There is a risk of bias, particularly selection bias, since the cases reported may not be representative of the general population.
- They may be influenced by chance events, leading to potentially false conclusions.
However, despite these limitations, descriptive studies are often the first step in identifying emerging public health issues, and they help inform more comprehensive studies.
6. Importance of Descriptive Studies in Public Health
Descriptive studies such as case reports and case series are crucial in public health because they:
- Provide early warning signs of emerging health issues, such as new diseases or unusual complications.
- Generate hypotheses that can be explored in larger, more rigorous studies.
- Offer detailed clinical insights into rare or novel conditions.
These studies help guide public health interventions, inform clinical practices, and shape future research priorities.
7. Practice Questions
Let’s practice some questions to reinforce your understanding of case reports and case series. Try answering these before checking the solutions.
Question 1:
A researcher documents a rare complication that occurred in a single patient who received a new medication. What type of descriptive study is this?
Answer 1:
Answer, click to reveal
This is a case report because it focuses on a single patient with a detailed account of a rare condition.
Question 2:
A study tracks 10 patients diagnosed with a rare disease to identify common clinical characteristics and outcomes. What type of study design is this?
Answer 2:
Answer, click to reveal
This is a case series because it involves multiple patients with the same condition and aims to identify trends.
Question 3:
What is a limitation of both case reports and case series?
Answer 3:
Answer, click to reveal
Both study designs cannot establish causality because they lack a comparison group.
8. Conclusion
Case reports and case series are invaluable tools in public health, providing detailed descriptions of health events and generating hypotheses for further study. While these descriptive studies cannot establish causality, they are often the first step in understanding rare or novel health conditions and identifying trends that warrant further investigation.
Always remember:
- Case Reports focus on detailed documentation of a single case or small number of cases.
- Case Series examine multiple cases with similar characteristics to identify trends or commonalities.
Final Tip for the CPH Exam:
Ensure you understand the differences between case reports and case series and their respective roles in public health research. Practice identifying which study design is appropriate for different types of research scenarios. This will prepare you for questions related to study designs on the CPH exam.
By following this structured approach, you should feel confident in addressing descriptive study questions, both on the exam and in real-world public health research.
Humanities Moment
The featured image for this article is Sumatra Bronze-Tailed Peacock Pheasant (1918-1922)by George Edward Lodge (English, 1860 – 1954). George Edward Lodge was a British bird illustrator and falconry expert, known for his work on various ornithological publications and his mastery of woodcuts. He contributed illustrations to major works on birds and published his own book, Memoirs of an Artist Naturalist (1946), while also establishing a trust fund for the publication of natural history works.