# odds ratio

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## odds ratio

ratio of two odds, but as used in the analysis of data from a case control study, a simple calculation, also called the cross-products ratio, which yields an approximate value for the relative risk of the exposure that has been examined in a case control study.

## odds ratio

Epidemiology Cross-product ratio, exposure odds ratio overdispersion A measure of association in a case-control study which quantifies the relationship between an exposure and health outcome from a comparative study. See Absolute risk reduction, Number needed to treat, Relative risk.## odds ratio

In epidemiological case-control studies, a relative measure of the occurrence of disease. The odds in favor of a particular disease occurring in an exposed group are divided by the odds in favor of its occurring in an unexposed group. If the condition being studied is rare, the odds ratio is a close approximation to the relative risk.

Synonym: *events odds ratio*See: relative risk

## odds

a method of expressing probability, e.g. at odds of 3 to 2 this can be converted to conventional terminology by using each number as the numerator and the sum of them as the denominator, i.e. 3/5, 2/5 or 60% or 40% or 0.6, 0.4. The odds are quoted as for or against. So that at odds of 3 to 2 the chances for an event happening are 3/5. The odds against it happening are 2/5.

**posterior odds**

probability determined after consideration of the results of a study.

**odds ratio**

the ratio, used particularly in case-control studies, estimates the chances of a particular event occurring in one population in relation to its rate of occurrence in another population.

## ratio

[L.] an expression of the quantity of one substance or entity in relation to that of another; the relationship between two quantities expressed as the quotient of one divided by the other. It differs from a proportion in that the numerator is not included in the denominator. Thus x/(x + y) is a proportion, x:y is a ratio.

**A-G ratio**

albumin-globulin ratio.

**area-incidence ratio**

the number of new cases of a specific disease in a population during a specified time period, divided by the geographic area size in which the observations are made, multiplied by the time elapsed, e.g. cases per hectare per month.

**arm ratio**

a figure expressing the relation of the length of the longer arm of a mitotic chromosome to that of the shorter arm.

**A/S ratio**

the diameter of the ascending aorta divided by the diameter of the aorta at the sinus of Valsalva; less than 1 in a normal dog. In subaortic stenosis it becomes greater than 1.

**cardiothoracic ratio**

the ratio of the transverse diameter of the heart to the internal diameter of the chest at its widest point just anterior to the dome of the diaphragm.

**cross ratio**

see odds ratio.

**fetal death ratio**

the number of fetal deaths divided by the number of live births.

**gain ratio**

individual animal's gain/average gain in group × 100.

**lecithin-sphingomyelin ratio**

the ratio of lecithin to sphingomyelin in amniotic fluid. See also lecithin, sphingomyelin.

**odds ratio**

see odds ratio.

**rates ratio**

the ratio between two rates. See odds ratio and relative risk ratio (below).

**relative risk ratio**

the ratio between the rate (of mortality or some such parameter) in one group of animals and the rate in another group, used as a standard and the comparison expressed as a ratio. See also relative risk.

**sex ratio**

the number of males in a population per number of females, usually stated as the number of males per 100 females.

**S/P ratio**

secondary-to-primary ratio. An indicator of fleece type in sheep, the greater the ratio the finer the fleece. Coarse-wool sheep have ratios of 3:1 to 4:1; merinos have a ratio of 20:1.

**stillbirth ratio**

the ratio of stillbirths to total births in the population.

**urea excretion ratio**

the ratio of the amount of urea in the urine excreted in one hour to the amount in 100 ml of blood. The normal ratio is 50.

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