THE PRECISION PROTOCOL
The Definitive Guide to USMLE Biostatistics.
Chapter 11: The Essential Formulas
To achieve the Standard of Excellence for a HIGH score, you cannot afford to hesitate during the exam. This final chapter is your "Pre-Surgical Checklist." These are the exact mathematical relationships and core concepts that must be second nature before you sit for the USMLE Step 1, Step 2 CK or Step 3.
1. The Diagnostic Master Suite
- Sensitivity: True Positives / (True Positives + False Negatives)
- Specificity: True Negatives / (True Negatives + False Positives)
- PPV (Prevalence Dependent): True Positives / (All Positives)
- NPV (Prevalence Dependent): True Negatives / (All Negatives)
- Likelihood Ratio (+): Sensitivity / (1 - Specificity)
- Likelihood Ratio (-): (1 - Sensitivity) / Specificity
2. The Impact and Risk Matrix
- Attributable Risk (AR): Risk in Exposed - Risk in Unexposed
- Relative Risk (RR): Risk in Exposed / Risk in Unexposed
- Odds Ratio (OR): (A x D) / (B x C)
- Absolute Risk Reduction (ARR): Risk in Control - Risk in Treatment
- Number Needed to Treat (NNT): 1 / ARR
- Number Needed to Harm (NNH): 1 / AR
3. The Precision and Distribution Map
- Standard Error (SEM): SD / sqrt(n)
- 95% Confidence Interval: Mean +/- (2 x SEM)
- Z-score: (Observed Value - Mean) / SD
- The Power Principle: Power = 1 - Beta (The ability to detect a difference)
- The 68-95-99.7 Rule: 1 SD = 68%, 2 SD = 95%, 3 SD = 99.7%
From the Founder & CMO
I know exactly where you are standing. I’ve been there. The difference between passing and achieving the Standard of Excellence isn’t about memorizing more—it’s about Surgical Precision. I built doctorenusa.com to give you the roadmap to mastery. This interactive eBook, The Precision Protocol, is the distillation of that strategy. It is a system designed to eliminate error and maximize clinical performance. Stop guessing. Start calculating." — Dr. Cristhian Feria, MD Founder & CMO, Doctor en USA
From the Chairman & Founder
Excellence is not an accident; it is the result of deliberate systems and superior design. As an educator and business strategist, my focus is ensuring that doctorenusa.com delivers more than just content—we deliver a high-performance academic environment. The Precision Protocol is the result of integrating advanced educational methodology with clinical mastery. We have engineered every chapter and every metric to ensure your preparation is organized, efficient, and results-driven. You provide the effort; we provide the infrastructure for your success." — Zuly Vallejo, MBA, M.Ed Chairman & Founder, Doctor en USA
Doctor en USA: Setting the standard for excellence as the #1 academic platform in medical education.
