An odd measure of risk: use and misuse of the odds ratio
Section snippets
Methods
The American Journal of Obstetrics and Gynecology and Obstetrics & Gynecology were searched from 1998 and 1999. Articles were selected using the search term “odds ratio” within PubMed (National Library of Medicine; http://www.ncbi.nlm.nih.gov/PubMed/). Each article was evaluated and classified by study type: cohort, case-control, randomized clinical trial, cross-sectional, or meta-analysis. The statistical method used to generate the odds ratios was classified as logistic regression or other
Results
During 1998–1999, 77 articles in the American Journal of Obstetrics and Gynecology and 77 articles in Obstetrics & Gynecology contained “odds ratio” when searched with PubMed. Three articles were excluded. One used the term “odds ratio” to describe a prevalence ratio; another did not contain an odds ratio computation; and the third was a review article with no information about how the odds ratio was computed. One hundred (66.2%) of the remaining 151 articles were cohort studies; 29 (19.2%)
Discussion
The odds ratio appears so often in clinical research reports because of its useful mathematical properties. The coefficients of logistic regression models convert readily into odds ratios, and the odds ratio is the measure of association derived from case-control data. There are situations (eg, comparing two proportions, both of which are close to one) when the odds ratio makes more “sense” than the risk ratio. However, in everyday situations we think more often in terms of risk ratios. We
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