An odd measure of risk: Use and misuse of the odds ratio

OBJECTIVE: To determine how often the odds ratio, as used in clinical resea rch of obstetrics and gynecology, differs substantially from the risk ratio estimate and to assess whether the difference in these measures leads to m isinterpretation of research results. METHODS: Articles from 1998 through 1999 in Obstetrics Gynecology and the A merican Journal of Obstetrics and Gynecology were searched for the term "od ds ratio." The key odds ratio in each article was identified, and, when pos sible, an estimated risk ratio was calculated. The odds ratios and the esti mated risk ratios were compared quantitatively and graphically. RESULTS: Of 151 studies using odds ratios, 107 were suitable to estimate a risk ratio. The difference between the odds ratio and die estimated risk ra tio was greater than 20% in 47 (44%) of these articles. An odds ratio appea rs to magnify an effect compared with a risk ratio. In 39 (26%) articles th e odds ratio was interpreted as a risk ratio without explicit justification . CONCLUSION: The odds ratio is frequently used, and often misinterpreted, in the current literature of obstetrics and gynecology. (C) 2001 by the Ameri can College of Obstetricians and Gynecologists.)