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Effect size (Relative risk vs odds ratio vs hazard ratio & NNT and NNH explained — This Is Why understanding these concepts is essential for interpreting clinical trials with Dr. Busti.
In this episode of This Is Why, Dr. Busti breaks down relative risk (RR), odds ratios (OR), absolute risk reduction (ARR), absolute risk increase (ARI), number needed to treat (NNT), and number needed to harm (MMH) in a way that connects directly to real clinical decision-making. This Is Why learning the “why” behind these calculations helps you move beyond memorization and actually apply evidence to patient care.
You’ll learn how to interpret whether a treatment increases or decreases risk, how to calculate and understand number needed to treat (NNT), and how to avoid common mistakes—like misinterpreting percentages or confusing statistical vs clinical meaning. Dr. Busti also walks through practical examples, including antihypertensive side effects, aspirin for MI prevention, and statin therapy, to show how these metrics influence real-world decisions.
Topics Covered:
- Definition of relative risk (risk ratio)
- When to use relative risk (RR) vs odds ratio (OR) vs hazards ratio (HR)
- Prospective vs retrospective study design
- Interpreting RR
- Confidence intervals and statistical significance
- Relative risk increase vs reduction
- Absolute risk reduction (ARR) explained
- Number needed to treat (NNT) & Number needed to harm (NNH) calculations
- Clinical vs statistical interpretation of risk
- Applying evidence to cost and patient outcomes
Chapter Table of Contents
00:00 - Introduction
02:52 - Effect Size Fundamentals
06:26 - Risk vs Odds Calculations
09:54 - Relative Risk (RR) & Relative Risk Increase
15:34 - Relative Risk Reduction (RRR)
19:04 - Absolute Risk Reduction (ARR) & Number Needed to Treat (NNT)
22:13 - Absolute Risk Increase (ARI) & Number Needed to Harm (NNH)
25:51 - Odds Ratio (OR): Interpretation & Pitfalls
32:14 - Hazard Ratio (HR) & Kaplan-Meier Concepts
34:45 - Confidence Intervals & Exam Pearls
36:31 - Conclusion
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#relativerisk #oddsratio #nnt #ebm #Dr Busti
Speaker:
Anthony Busti, MD, PharmD, MSc, FAHA, FNLA, is a licensed healthcare professional and medical educator with over 30 years of experience in clinical practice and academic teaching. He has trained and practiced as a nurse, pharmacist, and physician, bringing a uniquely comprehensive perspective to patient care and medical education.
Dr. Busti is dedicated to advancing evidence-based medicine and helping clinicians understand the underlying “why” behind clinical decisions to improve patient outcomes.
About This Channel:
This content is created by Anthony Busti, MD, PharmD, MSc, FAHA, FNLA, a board-certified physician with training at Johns Hopkins School of Medicine and University of Oxford and a medical educator for healthcare professionals and students. All material is based on current medical literature and evidence-based guidelines that align with principles of evidence-based medicine (EBM) and Evidence-Based Healthcare (EBHC).
Disclaimer:
This content is for educational purposes only and is not medical advice. It does not replace individualized evaluation, diagnosis, or treatment. Always seek the advice of a qualified health provider with questions about a medical condition and never delay care because of educational content.
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