USMLE purpose: Solve viewer-style relative risk and study-design questions by reading the final sentence first and identifying what comparison is being requested.

How to use this page

  1. Read the final sentence first: what metric are they asking for?
  2. For ratio questions, place the first mentioned group on top and the comparison group on bottom.
  3. For study design questions, ask whether anyone had the outcome at the start.
  4. Open the answer toggles only after attempting each question.

One-liner

For relative-risk comparison questions, the phrase “A compared to B” means calculate A ÷ B.

High-yield rules from this episode

Rule How to use it Example
First group goes on top “Heavy vapers compared to non-vapers” = heavy vapers / non-vapers 0.5 ÷ 0.1 = 5
Case-control → odds ratio Starts with diseased vs non-diseased Rare disease, retrospective exposure
Cohort → relative risk Starts with exposed vs unexposed, outcome develops later Vaccinated vs unvaccinated followed for headaches
Incidence New cases over time Risk during follow-up

Anki-style rapid recall

Practice Questions

Question 1

The risk is 0.5 in heavy vapers and 0.1 in non-vapers. What is the relative risk for heavy vapers compared with non-vapers?