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Different Forms of Medical Trials and Studies
Related Subjects: |Basic Statistics |Sampling in Medical Statistics |Reading a Medical paper |Different Forms of Medical Trials and Studies |Hierarchy of Evidence-Based Trials
🔍 Observational Studies
- 👥 Cohort Studies: Follow a group over time to see how exposures affect outcomes.
➡ Can be prospective (looking forward) or retrospective (using existing records).
📊 Often used in epidemiology (e.g. smoking → lung cancer risk). Strong for incidence but can be costly and time-consuming. - ⚖️ Case-Control Studies: Compare people with a disease (cases) to those without (controls).
➡ Good for rare conditions (e.g. mesothelioma and asbestos).
⚠️ Prone to recall bias because it relies on past exposures. - 📸 Cross-Sectional Studies: Snapshot of a population at one time, measuring both exposures and outcomes.
➡ Useful for prevalence (e.g. obesity rates in the UK).
⚠️ Cannot prove cause and effect.
💊 Interventional Studies (Clinical Trials)
- 🎲 Randomized Controlled Trials (RCTs):
- Participants randomly assigned to intervention vs control.
- Gold standard for testing efficacy ✅ — minimizes bias, forms much of NICE evidence base.
- 📑 Non-Randomized Controlled Trials:
- Allocation not random — used where randomisation is unethical or impractical.
- ⚠️ More prone to bias but still informative.
- 🧪 Single-Arm Trials:
- All participants receive the same treatment.
- Often early-phase (Phase I/II) studies for safety, dose-finding, or feasibility.
📚 Other Study Designs
- 📝 Case Reports & Case Series:
- Case Report: Detailed story of a single patient (e.g. the first report of AIDS in the 1980s).
- Case Series: Several linked cases — can hint at emerging patterns.
- 📖 Systematic Reviews & Meta-Analyses:
- Systematic Review: Comprehensive literature search + appraisal. Provides an overview of all evidence.
- Meta-Analysis: Pools data statistically to give overall effect size.
🔺 Often sits at the top of evidence hierarchies used by NICE/WHO.
- 🔄 Adaptive Trials:
- Trial design can be modified after interim results (e.g. dose adjustment, dropping ineffective arms).
- Useful in rapidly evolving fields like oncology or pandemic research.
- 🌍 Pragmatic Trials:
- Designed for real-world NHS practice, not just ideal lab conditions.
- Broad eligibility, flexible protocols — tells us if a treatment works in day-to-day clinical life.
🧠 Key Considerations in Medical Studies
- 📐 Study Design: Must fit the research question — wrong design = misleading conclusions.
- 🔢 Sample Size: Too small risks false negatives; too large can make trivial effects “statistically significant.”
- 🎲 Randomisation & Blinding: Critical in trials to reduce bias.
- 📊 Statistical Analysis: Look beyond p-values — confidence intervals and effect sizes matter.
- ⚖️ Ethics: Patient consent, data protection, and safety monitoring (essential under GMC & NHS guidelines).
🏁 Conclusion
- Understanding study designs helps doctors and students judge whether evidence is valid, reliable, and applicable.
- This skill underpins evidence-based medicine in both exams and clinical practice 🚀.