Odds ratio
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The odds ratio is a technical term often used in medical statistics. The odds ratio is the ratio of the relative incidence of a target disorder in the experimental group relative to the relative incidence in a control group. Essentially, it reflects how the risk of having a particular disorder is influenced by the treatment. An odds ratio of 1 means that there is no benefit of treatment compared to the control group.[1]
The odds ratio is a difficult concept and recommendations for how to teach its use are available.[2]
Example
This example is from the Titanic (example from Power[3]):
Male passengers:
142 survived, 709 died
- Odds of survival = 142/709 = 0.20
- Probability (risk or chance) of survival = 142/(142+709) = 17%
Female passengers:
308 survived, 154 died
- Odds of survival = 308/154 = 2.00
- Probability (risk or chance) of survival = 308/(308+154) = 67%
Comparison:
- Odds ratio (OR) for survival = 0.20/2.00 = 0.10
- Relative risk (RR) for survival = 17%/67% = 0.25
References
- ↑ Anonymous. Odds and odds ratio. Bandolier.
- ↑ Prasad K, Jaeschke R, Wyer P, Keitz S, Guyatt G (May 2008). "Tips for teachers of evidence-based medicine: understanding odds ratios and their relationship to risk ratios". J Gen Intern Med 23 (5): 635–40. DOI:10.1007/s11606-007-0453-4. PMID 18181004. Research Blogging.
- ↑ Power M (2008). "Resource reviews". Evidence-based Medicine 13 (3): 92. PMID 18515638. [e]