Odds ratio
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
Interpretation
The odds ratio is generally used to measure the association between a risk factor and disease. However, using the odds ratio to measure the ability of a risk factor to diagnose disease is problematic.[4] The odds ratio should be at least 16 to have reasonable diagnostic ability.[5]
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]
- ↑ Boyko EJ, Alderman BW (1990). "The use of risk factors in medical diagnosis: opportunities and cautions". J Clin Epidemiol 43 (9): 851–8. PMID 2213074. [e]
- ↑ Pepe MS, Janes H, Longton G, Leisenring W, Newcomb P (May 2004). "Limitations of the odds ratio in gauging the performance of a diagnostic, prognostic, or screening marker". Am. J. Epidemiol. 159 (9): 882–90. PMID 15105181. [e]