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Guyatt G, Rennie D, Meade MO, Cook DJ
Part B Therapy
Chapter 10.2. Understanding the Results: More About Odds Ratios
Roman Jaeschke, Stephen Walter, Mahmoud El Barbary, Gordon Guyatt
Table 10.2-2 Results From a Randomized Trial of Endoscopic Sclerotherapy Compared With Endoscopic Ligation for Bleeding Esophageal Varicesa


Topics Discussed: 2x2 table, interpretation of results, odds ratios (relative odds), understanding the results

Excerpt: "As clinicians, we are interested less in rolling dice than in treating patients. So, in terms of odds, we are interested in the odds of experiencing an adverse outcome vs avoiding that outcome. Further, we are interested in those odds in patients exposed to treatment vs those not exposed. When we compare odds from treated and untreated groups, we will end up with the ratio of 2 odds, not surprisingly called odds ratio (OR). In Chapter 7, Does Treatment Lower Risk? Understanding the Results, in which we discussed ways of presenting the magnitude of a treatment effect, we introduced the concept of the OR. To help understand it, we present once again the 2 x 2 table (Table 10.2-1) and the results from ligation vs sclerotherapy of bleeding esophageal varices (Table 10.2-2).1 In this and other examples in this chapter, we look at situations in which a treatment may reduce the probability of an adverse event, and thus an OR less than 1.0 represents a benefit of treatment (OR > 1 is associated with increased odds of that event happening, whereas OR of 1 describes no effect)...."
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