A case series describes two or more patients who have the same disease or underwent the same procedure. Case series are used to describe characteristics of a group, identify new syndromes, clarify disease progression, and develop hypotheses for future research. Sample sizes may range from a few patients for rare conditions to several hundred. Researchers establish clear inclusion and exclusion criteria when defining cases. Data is collected primarily from patient interviews and medical records. Analysis typically involves counting symptoms and frequencies rather than complex statistics.

2. Chapter 9
Case Series

3. Overview
A case report describes one patient.
A case series describes two or more patients
who have the same disease condition or who
have undergone the same procedure.

4. Uses of Case Series
• Describing the characteristics of and
similarities among a group of individuals with
the same signs and/or symptoms of disease
• Identifying new syndromes and refining case
definitions.
• Clarifying typical disease progression
• Developing hypotheses for future research

5. Sample Size
• Some case series for rare conditions may
require only a few participants
• Other studies may include several hundred
individuals

6. Getting Started…
• Select one disease or condition of interest
• Determine what will be new and interesting
about the study
• Identify an appropriate and available source of
cases
• Establish a clear case definition that spells out
inclusion criteria and exclusion criteria.

7. Case Definitions
Specify characteristics related to:
•The disease or procedure
– ICD codes (International Classification of Diseases
codes) are often used as part of the definition
•Person
•Place
•Time

8. FIGURE 9-2 Sample Case Definitions

9. Data Collection
• Primary data: interviews of cases using a
questionnaire and/or qualitative techniques
• Secondary data from patient charts (medical records)
– It is often helpful to create a questionnaire that
guides the extraction of information from medical
records
– Be aware that patient charts are often incomplete;
missing information about a symptom does not
mean that the patient did not experience it

10. Analysis
Most case studies do not require any numbers
beyond simple counts and frequencies.

11. FIGURE 9- 1 Key Characteristics
of a Case Series