Free study tools/Biostatistics
THE STEP 3 BIOSTATISTICS LAB
Make the numbers
make sense.
One question. A clear explanation. A better grasp of the next one.
Practice the calculation.
Understand the conclusion.
Original educational questions · Not official USMLE itemsProgress stays in this browser
Your practice record
Counts include answered questions from Learn, Practice and completed timed sets. This is practice accuracy, not an exam score prediction. Progress is local to this browser; unfinished sets are not saved.
SEE THE RELATIONSHIP
The same test.
A different population.
Move the sliders. Watch the expected results for 10,000 people change.
Positive predictive value
Negative predictive value
SMALL SESSIONS. CLEARER THINKING.
Build understanding,
one denominator at a time.
Work through test accuracy, predictive values, risk and odds, treatment effects, likelihood ratios, confidence intervals and study design. Numerical questions vary the values; interpretation questions use a curated set of scenarios.
Timed sets contain 10 mixed questions with a 15-minute practice limit. This is a study setting, not a reproduction of an official exam block.
Make room for practice in your study plan →NEXT: MANAGE THE PATIENT
Bring the decisions together.
Practice full CCS cases, reassess your patient and learn from your decisions with CCS Orbit.
Explore CCS Orbit →Coming to iPhone · Three free cases at launch
Methodology & references
All scenarios and counts are illustrative. Diagnostic measures use the labeled reference-standard table. Treatment examples use a one-year follow-up; NNT and NNH use absolute risk differences as proportions and round up. Ratios are rounded to two decimals, percentages to one decimal where needed. Keep full precision until the final step.
Questions are for exam preparation, not patient-care decisions. The tool does not estimate your USMLE score.
- CDC: epidemiologic measures and diagnostic test formulas
- CDC Field Epidemiology Manual: associations, study design and interpretation
- Cochrane Handbook: absolute effects and numbers needed to treat
- BMJ: diagnostic likelihood ratios
- American Statistical Association: significance and uncertainty
Updated October 13, 2026 · CCS Orbit