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The odds ratio divides the odds in the exposed group by the odds in the reference group. For our hypothetical example, the odds of hypertension for drinkers is 50%/50% or 1 to 1; and the odds for nondrinkers is 25%/75% or 1 to 3; thus, the odds ratio is OR 50%⁄50% ⁄ 25%⁄75% 3.0, or, equivalently, OR 1⁄1 ⁄ 1⁄3 3.0.
odds ratios approximate relative risk ratios, when the outcomes are not rare, odds ratios always overestimate relative risk ratios, a problem that becomes more acute as the baseline prevalence of the outcome exceeds 10%. Odds ratios cannot be calculated directly from relative risk ratios. For example, an odds ratio for
This simplistic dictionary definition of the probable quality attached to an event is unanimously accepted in current speech. Far from standing for a rigorous definition, this enunciation still gives evidence for the quantitative and measurement aspect of the probability concept because the chance of an event occurring is
The odds ratio is a measure of an association on a ratio scale, so percentage differences are not meaningful, such as (1 − 0.28) × 100 = 72%. When odds ratios are used to indicate risk, it is necessary to consider ratios when differences are expressed in terms of percentage of change.
Definition of Odds The odds of an event occurring is the ratio of the number of ways the event can occur (successes) to the number of ways the event cannot occur (failures).
Sep 14, 2016 · ORs are often interpreted as though they have the same meaning as RRs (i.e., ratios of probabilities rather than ratios of odds), an interpretation that is incorrect in cross-sectional and longitudinal analyses.
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Sep 11, 2015 · see odds ratios (ORs) being used in research to explain whether interventions contribute to improvements in health. They are used to help researchers demon-strate associations between interventions and out-comes in both positive and negative directions. To explain how ORs are calculated and what they mean, we will use two examples.
