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==== Relative risk ==== The [[relative risk]] (RR), also called '''risk ratio''', is simply the risk (probability) of an event relative to some independent variable. This measure of effect size differs from the odds ratio in that it compares ''probabilities'' instead of ''odds'', but asymptotically approaches the latter for small probabilities. Using the example above, the ''probabilities'' for those in the control group and treatment group passing is 2/3 (or 0.67) and 6/7 (or 0.86), respectively. The effect size can be computed the same as above, but using the probabilities instead. Therefore, the relative risk is 1.28. Since rather large probabilities of passing were used, there is a large difference between relative risk and odds ratio. Had ''failure'' (a smaller probability) been used as the event (rather than ''passing''), the difference between the two measures of effect size would not be so great. While both measures are useful, they have different statistical uses. In medical research, the [[odds ratio]] is commonly used for [[case-control study|case-control studies]], as odds, but not probabilities, are usually estimated.<ref>{{cite journal |author = Deeks J |year = 1998 |title = When can odds ratios mislead? : Odds ratios should be used only in case-control studies and logistic regression analyses |journal = BMJ |volume = 317 |issue = 7166 |pages = 1155β6 |pmid = 9784470 |pmc = 1114127|doi=10.1136/bmj.317.7166.1155a }}</ref> Relative risk is commonly used in [[randomized controlled trial]]s and [[cohort study|cohort studies]], but relative risk contributes to overestimations of the effectiveness of interventions.<ref name="Stegenga2015">{{Cite journal | last1 = Stegenga | first1 = J. | title = Measuring Effectiveness | journal = Studies in History and Philosophy of Biological and Biomedical Sciences | volume = 54 | pages = 62β71 | year = 2015 | url = https://www.academia.edu/16420844 | doi=10.1016/j.shpsc.2015.06.003| pmid = 26199055 }}</ref>
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