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Biostatistics on the USMLE

USMLE biostatistics and epidemiology questions appear on every Step, and they count most on Step 3. In USMLE’s specifications the area is 4-6% of Step 1, 3-5% of Step 2 CK and 11-13% of Step 3 multiple-choice questions, where it’s grouped with interpreting the medical literature. The 2026 outline lists topics from study design to bias and screening tests.

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Updated October 2026 · Written from official sources, listed at the bottom of this page

How much USMLE biostatistics is on each Step?

On Step 3 it’s the largest single area, and it sits on Day 1, Foundations of Independent Practice. The CCS cases on Day 2 don’t cover it.

StepArea in the specificationsShare of questions
Step 1Biostatistics and epidemiology/population health4-6%
Step 2 CKBiostatistics, epidemiology/population health and interpretation of the medical literature3-5%
Step 3Biostatistics, epidemiology/population health and interpretation of the medical literature11-13%

What the outline lists

  • Epidemiology: incidence and prevalence, rates, life expectancy, attack rate, herd immunity, vaccine effectiveness and outbreak investigation.
  • Study design: case series, cross-sectional, case-control and cohort studies, randomized trials, and systematic reviews and meta-analysis.
  • Measures of association: relative risk, odds ratio, hazard ratio, number needed to treat or harm, and attributable risk.
  • Testing and screening: sensitivity, specificity, predictive values, ROC curves, likelihood ratios, and lead-time and length bias.
  • Interpreting studies: type I and II errors, power, p-values, confidence intervals, chi-square and t-tests, confounding, and bias, including recall and ascertainment bias.
  • Research ethics: informed consent, IRBs, patient privacy, and the phases of drug approval.

How to study biostatistics for Step 3

Step 3 gives this area more weight than the other Steps, and adds interpreting the medical literature to it. So practice reading an abstract, a table or a graph and deciding what it means for a patient: the outline lists interpreting graphs, tables and text, and applying study results to patient care, under this area.

USMLE’s free sample questions include biostatistics items for each Step, and our 20-question practice set has a few too.

Free official sample questions →Our 20 practice questions →USMLE Step 3 →

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Sources: USMLE and 5 more. Checked October 2026.

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