Overview
This lecture introduces key types of epidemiological studies, explaining their purposes, major features, and the advantages and disadvantages of each.
What is an Epidemiological Study?
- An epidemiological study is a scientific process to answer a question about a population using data.
- Steps include formulating a study question, choosing a study type, collecting/analyzing data, interpreting results, and reporting, all ethically.
Types of Epidemiological Studies
Ecological Studies
- Measure disease rates and exposures in groups, not individuals.
- Useful for comparing health across places or times and for generating new research questions.
- Findings apply to groups, not individuals.
Case Series
- Describe characteristics of people with the same disease or exposure.
- Help understand demographics, clinical features, prognosis, or unusual disease patterns.
Cross-Sectional Studies
- Collect data on health and exposures at a single point in time ("snapshot").
- Often use questionnaires; also called prevalent studies.
- Useful for assessing population health needs; cannot determine causation.
- Relatively cheap and easy to conduct.
Case-Control Studies
- Compare people with a disease (cases) to similar people without the disease (controls) for past exposures.
- Calculate odds ratio to identify possible risk or protective factors.
- Useful for rare diseases and outbreaks; quick and inexpensive.
- Limited for rare exposures; subject to recall bias; finding matched controls can be difficult.
Cohort Studies
- Follow groups over time to track disease occurrence based on exposure.
- Calculate relative risk to measure the association between exposure and outcome.
- Advantages: Establish time sequence; collect data on many risk factors and outcomes.
- Disadvantages: Expensive, long-term, large sample needed; not suited for rare diseases; risk of participant dropout.
Interventional (Experimental) Studies
- Apply interventions (e.g., drug, vaccine) and compare outcomes to a control group.
- Randomized controlled trials (RCTs) randomly assign participants to groups and use blinding to avoid bias.
- Advantages: Strong evidence that intervention caused outcome.
- Disadvantages: Expensive, large sample needed, may be unethical or impractical in some situations.
Reviews and Meta-Analyses
- Systematic reviews collect and assess all relevant studies to summarize evidence on a topic.
- Meta-analyses statistically combine data from similar studies to produce a single summary result.
Key Terms & Definitions
- Ecological study — research measuring exposures and disease in groups rather than individuals.
- Case series — description of characteristics among people with the same disease/exposure.
- Cross-sectional study — measures health status/exposures at one time in a population.
- Case-control study — compares past exposures in diseased (cases) and non-diseased (controls) groups.
- Odds ratio — measure comparing odds of exposure between cases and controls.
- Cohort study — follows exposed and unexposed groups over time to track outcomes.
- Relative risk — ratio of disease risk in exposed versus unexposed groups.
- Randomized controlled trial (RCT) — experimental study where participants are randomly assigned to groups.
- Systematic review — summary of all quality evidence on a topic.
- Meta-analysis — pooled statistical analysis of data from multiple similar studies.
Action Items / Next Steps
- Review definitions and examples for each study type.
- Practice identifying which study design is best for different research questions.