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Definition of Odds ratio

Odds ratio Definition from Science & Technology Dictionaries & Glossaries
Electronic Statistics Textbook
The odds ratio is useful in the interpretation of the results of Logistic regression (see Neter, Wasserman, and Kutner, 1989) and is computed from a 2x2 classification table which displays the predicted and observed classification of cases for a binary dependent variable:
(f11 * f22)/(f12 * f21)
where fij represents the respective frequencies in the 2x2 table.
Common Concepts in Statistics
The ratio of the odds of the risk factor in a diseased group and in a non-diseased (control) group. The odds ratio is used in retrospective case-control studies (relative risk is the ratio of proportions in two groups which can be estimated in a prospective study). Odds ratio and relative risk are usually considered interchangeable especially for large samples and are calculated as ad/bc where a,b,c,d are the entries in a 2x2 contingency table (hence the alternative definition as the cross-product ratio). In logistic regression, the coefficient corresponds to the of the odds ratio. There are statistical methods to test the homogeneity of odds ratios. (Online Odds-Ratio Calculation.)
Odds ratio Definition from Encyclopedia Dictionaries & Glossaries
English Wikipedia - The Free Encyclopedia
In statistics, the odds ratio (usually abbreviated "OR") is one of three main ways to quantify how strongly the presence or absence of property A is associated with the presence or absence of property B in a given population. If each individual in a population either does or does not have a property "A", (e.g. "high blood pressure"), and also either does or does not have a property "B" (e.g. "moderate alcohol consumption") where both properties are appropriately defined, then a ratio can be formed which quantitatively describes the association between the presence/absence of "A" (high blood pressure) and the presence/absence of "B" (moderate alcohol consumption) for individuals in the population. This ratio is the odds ratio (OR) and can be computed following these steps:
  1. For a given individual that has "B" compute the odds that the same individual has "A"
  2. For a given individual that does not have "B" compute the odds that the same individual has "A"
  3. Divide the odds from step 1 by the odds from step 2 to obtain the odds ratio (OR).

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Odds ratio Definition from Medicine Dictionaries & Glossaries
Glossary of Epidemiology Terms
A measure of association which quantifies the relationship between an exposure and health outcome from a comparative study; also known as the cross-product ratio.
A statistical calculation in a case-control study involving the ratio of risk of an exposed group to that of an unexposed group. An O/R=2 means that the exposed group has twice the risk of the non-exposed group.
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Hepatitis Central (TM) Liver Disease Medical Glossary
A comparison of the presence of a risk factor for disease in a sample of diseased subjects and non diseased controls. The number of people with disease who were exposed to a risk factor (Ie) over those with disease who were not exposed (Io) divided by those without disease who were exposed (Ne) over those without who were not exposed (No). Thus OR=(Ie/Io)/(Ne/No)= Ie No / Io Ne. This measure should be used for case control studies where we retrospectively look at risks in those with and without disease. Also known as exposure odds ratio
Aids Glossary
a statistical measure of the likelihood of developing a disease or condition if exposed to a certain factor or pathogen.