```Date: Fri, 3 Jan 1997 09:28:16 -0800 Reply-To: Simo Virtanen Sender: "SAS(r) Discussion" From: Simo Virtanen Organization: Finnish Institute of Occupational Health Subject: Re: Odds Ratios Content-Type: text/plain; charset=us-ascii Paul Robertson wrote: ----- cut ----- > sepsis and trauma patients. The odds ratio I obtained > was about 4. > > How does this square with the fact that the mortailty > for the sepsis patients was 53% and for the trauma > patients it was about 22%? Is the problem the intercept? > When I ran the logistic regression without an intercept > the odds ratio obtained was around 1.3. -- dividing 53 by > 22 would indicate about twice the risk of death. right? No, an odds ratio of about 4 seems right to me. The **odds** for the first group would be 53/47=1.127, and odds for the second group would be 22/78=0.282. Then **odds ratio** would be 1.127/0.282=3.996. Note that the odds are defined as chances of being in one category as opposed being in others. -- Simo V. Virtanen, Ph.D. Finnish Institute of Occupational Health Helsinki, FINLAND ```

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