{
  "schema": "vedokrok.public-item.v1",
  "release_id": "MHC-RPUB-20261011-9e4b62c5",
  "url": "/knowledge/do-not-read-an-odds-ratio-as-a-risk-ratio",
  "id": "MHC-D-RESEARCH-0050",
  "version": "0.1.0",
  "title": "Do not read an odds ratio as a risk ratio",
  "summary": "The denominator changes the story.",
  "kind": "concept",
  "body": "Risk compares events with everyone; odds compare events with non-events. Check which quantity the paper reports before using words such as 'twice as likely'.",
  "limits": [
    "An odds ratio alone does not give an event probability. The fictional example illustrates arithmetic, not anyone’s personal risk."
  ],
  "topics": [],
  "intents": [
    "understand-a-decision"
  ],
  "source_ids": [
    "cochrane-effect-measures"
  ],
  "evidence": [
    {
      "claim": "Risk differences, risk ratios and odds ratios are different quantities.",
      "source_id": "cochrane-effect-measures",
      "role": "supports",
      "note": "Claim basis: technical_definition. Claim limit: Illustrative arithmetic is not a personal risk estimate.\nSource access: selected_html_passages; accessed on: 2026-09-17; inspected sections: [\"6.1-6.2\", \"6.4.1\", \"6.5.1 and MECIR C61\"].\nSource note: Handbook methodological guidance, not a recent intervention trial. Numerical examples in the elements are invented teaching examples.\nAgent scope review, 2026-10-11: Cochrane 6.4.1 defines risks and odds. The fictional 20%/40% example gives RR=2 and OR=8/3; no personal-risk or treatment claim.",
      "locator": "6.4.1"
    }
  ],
  "use_when": [
    "A study's odds ratio is being retold as a direct change in probability."
  ],
  "avoid_when": [
    "An odds ratio alone does not give an event probability. The fictional example illustrates arithmetic, not anyone’s personal risk."
  ],
  "example": "In a fictional sample, probabilities of 20% and 40% give a risk ratio of 2. Their odds are 0.25 and about 0.667, giving an odds ratio of about 2.67.",
  "check": "Did your summary preserve the reported measure instead of swapping its name?",
  "published_at": "2026-10-11T18:15:00Z",
  "review": {
    "kind": "agent",
    "label": "Agent editorial and scoped evidence review",
    "reviewed_at": "2026-10-11T18:12:50Z"
  },
  "editorial_overlay": null,
  "editorial": null,
  "notices": [],
  "sources": [
    {
      "id": "cochrane-effect-measures",
      "title": "Chapter 6: Choosing effect measures and computing estimates of effect",
      "url": "https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-06"
    }
  ],
  "relations": [],
  "collections": [
    {
      "id": "RC-D4FD0B28897E9517",
      "title": "Check what a study can actually tell you",
      "url": "/collections/check-what-a-study-can-actually-tell-you"
    }
  ],
  "topic_hubs": [],
  "solution_packs": []
}