Odds ratio
Odds Ratio
The Odds Ratio (pronunciation: /ɒdz ˈreɪʃɪəʊ/) is a statistical term that measures the strength of association between two binary data values, often used in epidemiological studies. It is a type of relative risk measure used frequently in case-control studies.
Etymology
The term "Odds Ratio" originates from the field of gambling, where "odds" refer to the likelihood of an event occurring. The term was later adopted in the field of statistics to describe the ratio of the odds of an event occurring in one group to the odds of it occurring in another group.
Definition
The Odds Ratio (OR) is defined as the ratio of the odds of an event occurring in the exposed group to the odds of the event occurring in the non-exposed group. It is calculated using the formula:
OR = (a/b) / (c/d)
where:
- a = number of cases with exposure and outcome
- b = number of cases with exposure but without outcome
- c = number of cases without exposure but with outcome
- d = number of cases without exposure and without outcome
Interpretation
An Odds Ratio of 1 implies that the event is equally likely in both groups. An OR greater than 1 implies that the event is more likely in the first group, and an OR less than 1 implies that the event is less likely in the first group.
Related Terms
- Confidence Interval: A range of values, derived from the statistical analysis, that is likely to contain the true Odds Ratio.
- Logistic Regression: A statistical method for analyzing a dataset in which there are one or more independent variables that determine an outcome, often used to calculate Odds Ratios.
- Risk Ratio: A comparison of the risk of a certain event happening in one group compared to the risk of the same event happening in another group.
External links
- Medical encyclopedia article on Odds ratio
- Wikipedia's article - Odds ratio
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