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Odds ratios and risk ratios: what's the difference and why does it matter?
1Department of Family Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. anthony_viera@med.unc.edu
Southern Medical Journal
|June 27, 2008
Summary
Odds ratios (OR) approximate relative risk (RR) when outcomes are rare. For common outcomes, ORs exaggerate RR, but RR can be estimated from OR using a formula. Understanding both measures improves research interpretation.
Area of Science:
- Epidemiology
- Biostatistics
Background:
- Odds ratios (OR) are frequently used in medical literature to quantify exposure-outcome associations.
- Relative risk (RR) is a more intuitive measure of association for the general audience.
Purpose of the Study:
- To clarify the relationship between odds ratios and relative risk.
- To provide guidance on interpreting these measures in medical research.
Main Methods:
- Comparison of OR and RR calculation methods in different study designs (cohort and case-control).
- Discussion of conditions under which OR approximates RR.
- Introduction of a method to estimate RR from OR.
Main Results:
- OR approximates RR when the outcome is uncommon (less than 10% in the unexposed group).
- OR exaggerates RR when the outcome is common (greater than or equal to 10% in the unexposed group).
- A simple formula exists to estimate RR from OR.
Conclusions:
- Understanding the distinction between OR and RR is crucial for accurate interpretation of research findings.
- Confidence intervals should accompany reported ORs and RRs for robust analysis.
- Readers can estimate RR from OR, especially when outcomes are common.
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