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From |
Jhilbe@aol.com |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: RE: ODDSRISK module to convert Logistic Odds Ratios to Risk Ratios |

Date |
Thu, 20 Dec 2007 12:00:23 EST |

'ODDSRISK': module to convert Logistic Odds Ratios to Risk Ratios now on SSC I thought I had posted a notice about this module to the list yesterday, but it seems that it did not make it. I take the Digest, so do not see what is posted until the next day. I apologize if the earlier one is posted today, as well as this one. Zhang and Yu (1998, JAMA) proposed an algorithm to convert binary logistic regression odds ratios to estimated risk ratios. I have seen the method used in a number of medical research articles, and had written about the method in a book I am writing. I noticed a couple of Statalist communications during the past couple of weeks related to the relationship of odds ratio to risk ratio. I wrote about this relationship in my "Negative Binomial Regression", but not about this method and its rationale. Anyhow, I thought it might be helpful to those interested in using this method to release a Stata implementation now rather than with the forthcoming book several months from now. I wrote the program in such a manner that the logistic odds ratio, estimated risk ratio, and 95% confidence intervals of the estimated risk ratios are displayed for each predictor in the model. The incidence rate of the unexposed risk factor, or primary predictor of interest (binary (1/0)), which is required for calculation, is also displayed. The estimated risk ratios are particularly important when we wish to use terms such as "likely" in place of "odds of" when interpreting the odds ratio of a logistic model. This is primarily the case with the odds ratio is under 0.5 or over 2.5 and the incidence rate is greater than 10%. To say something like, "patients having an anterior infarct are 50% more likely to die within 48 hours of hospital admission than are patients having just sustained an infarct at another primary site", is using risk language. Such language may be justified for many logistic models, but not all. Using the estimated risk values and CI's calculated by -oddsrisk- presumably enhance the justification for using risk language with logistic models when the conditions specified above obtain. Kit Baum has graciously posted the program, called -oddsrisk- and the associated help file to the SSC site. You can download it by typing . ssc install oddsrisk on the Stata command line. I have pasted the SSC site module description under my name below. Best, Joseph Hilbe DESCRIPTION/AUTHOR(S) oddsrisk converts logistic regression odds ratios to relative risk ratios. When the incidence of an outcome is common in the study population; i.e. greater than 10%, the logistic regression odds ratio no longer approximates the risk ratio. As the incidence rate becomes more frequent, the more the odds ratio overestimates the risk ratio when its value is greater than 1, and the more it underestimates the risk ratio when under one. J. Zhang and K. Yu proposed a method of adjusting the logistic regression odds ratio in a cohort study or clinical trial so that it approximates the risk ratio. This is particularly important when the odds ratio is greater than 2.5 or under 0.5. The method has also been shown to be applicable for retrospective and observational studies as well. Author: Joseph M. Hilbe Arizona State University jhilbe@aol.com or hilbe@asu.edu **************************************See AOL's top rated recipes (http://food.aol.com/top-rated-recipes?NCID=aoltop00030000000004) * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: RE: ODDSRISK module to convert Logistic Odds Ratios to Risk Ratios***From:*Ricardo Ovaldia <ovaldia@yahoo.com>

**Re: st: RE: ODDSRISK module to convert Logistic Odds Ratios to Risk Ratios***From:*Ricardo Ovaldia <ovaldia@yahoo.com>

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