Epidemiological Studies

What is a Study?

• A scientific process to answer a question using data from a population.
• Steps include:
  • Formulating a study question.
  • Deciding on the best study type.
  • Conducting the study, collecting, and analyzing data.
  • Interpreting results.
  • Reporting results ethically.

Types of Epidemiological Studies

1. Ecological Study

• Measurements on groups (e.g., people in a house or country).
• Results/conclusions apply to groups, not individuals.
• Useful for comparing health across populations or times.
• Generates questions and highlights issues for future studies.

2. Case Series

• Describes characteristics of a group with the same disease/exposure.
• Aims to understand demographics, clinical presentation, prognosis.
• Example: Early 1980s, unusual pneumonia led to HIV recognition.

3. Cross-Sectional Study

• Measures health information at a point in time (snapshot).
• Involves questionnaires/surveys.
• Known as prevalence studies.
• Pros:
  • Inexpensive, easy to conduct.
  • Provides info on multiple exposures and outcomes.
• Cons:
  • Cannot determine cause from single time data.

4. Case-Control Study

• Starts with cases (with disease) and controls (without disease).
• Compares past exposures to risk factors (odds ratio).
• Pros:
  • Quick, inexpensive.
  • Suitable for uncommon diseases.
• Cons:
  • Not good for rare exposures.
  • Difficulty finding matched controls.
  • Reliant on accurate past exposure recall.

5. Cohort Study

• Follows a group over time, collecting risk factor info.
• Compares outcome occurrence between exposed and unexposed.
• Uses relative risk measurement.
• Pros:
  • Determines time sequence of events.
  • Collects diverse data for sub-analysis.
• Cons:
  • High cost, not for rare diseases.
  • Retention over time is challenging.

6. Interventional Study

• An intervention (e.g., drug, vaccine) and its outcomes studied.
• Randomized controlled study is the best design.
• Pros:
  • Provides evidence of intervention impact.
  • Randomization ensures balanced comparison.
• Cons:
  • Expensive, may require many participants.
  • Ethical concerns in withholding interventions.

Summarizing Studies

Systematic Review

• Systematically identifies, assesses, synthesizes studies.
• Provides balanced summary of evidence.

Meta-Analysis

• Combines data from similar studies.
• Produces single statistical summary result.

Conclusion

• Overview of study types, their unique advantages, and limitations.