Module 6: Odds Ratios vs Risk Ratios

Module 6: Odds Ratios vs Risk Ratios

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This is a critical interpretation module for epidemiology and health research. The uploaded notes emphasize a practical rule: when the outcome is rare, odds ratios and risk ratios are close, but when the outcome is common, odds ratios can diverge substantially and overstate the apparent magnitude of association.

The module also highlights why risk ratios are often easier to explain to clinicians and policymakers, while odds ratios arise naturally in logistic regression and remain mathematically convenient.

Simple guide

  • Rare outcomes: OR and RR are often similar.
  • Common outcomes: divergence becomes important.
  • Always report clearly whether you are talking about odds, risk, or probability.

Example language

Risk ratio: the event is 1.8 times as likely in one group as in another.

Odds ratio: the odds of the event are 1.8 times as high in one group as in another.

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