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From |
"Michael I. Lichter" <mlichter@buffalo.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: Odds ratio |

Date |
Fri, 09 Apr 2010 14:09:53 -0400 |

Joseph (and anybody else),

Michael jhilbe@aol.com wrote:

I agree with Rich regarding the bias that can be produced in usingoddsrisk. Thereare some situations for which it is acceptable, but mostly it is not.I wrotethe command to provide it for those who wanted to use it - not toadvocate itsuse. The method was proposed in an article by Zhang and Yu in 1998 inJAMA -- Journal of the American Medical Association, presumably one ofthemost elite of medical journals. So it gained considerable popularity.I discuss the method in some length in my book "Logistic RegressionModels",pointing out its problems,but also when it can be used. I also offergeneral guidelinesof when it is acceptable to use a risk-probability interpretation forodds ratios, andprovide the calculations required to make the determination. Joseph Hilbe Date: Thu, 08 Apr 2010 16:21:49 -0400 From: Richard Goldstein <richgold@ix.netcom.com> Subject: Re: st: RE: Odds ratio well, first, I disagree with Paul's recommendation of -oddsrisk- there is now lots of evidence that this algorithm is biased; for results, and other ways of translating OR to RR see Blizzard, L and Hosmer, DW (2006), "Parameter estimation and goodness-of-fit in log binomial regression," _Biometrical Journal_, 48: 5-22; for a different way of looking at this, with Stata code, see, Localio, AR, Margolis, DJ and Berlin, JA (2007), "Relative risks and confidence intervals were easily computed indirectly from multivariable logistic regression," _Journal of Clinical Epidemiology_, 60: 874-882 second, if the OP really wants to present things in terms of changes inprobability, I recommend looking at Scott Long's -spostado- (-finditspostado-)Rich On 4/8/10 4:05 PM, Visintainer, Paul wrote:Rosie,Many health professionals find the ORs difficult to interpret,especially if the base proportion is common. It doesn't sound like the reviewer is questioning your analysis, just the way you present the results -- and,depending on your study, the ORs may look rather strange. Forexample, if youdid a survey, and 60% of one group answered a question positively,while 90% ofanother group answered it positively, your OR would be 6.0. This canbe quiteconfusing for someone trying to interpret this OR like a relative risk.One approach might be to try a program by Joseph Hilbe, called-oddsrisk-. Itwill convert ORs from a logistic regression to a relative risk with95%CIs. Inthe example above, the OR was 6, but the conversion gave 1.5 (e.g.,.90/.60 =1.5). This probably will make more sense to certain readers.Note that using the term "relative risk" depends on your study. Ifyourlogistic model was developed on a survey (e.g., cross-sectional), thenyour ORsare prevalence ORs. If you convert them using the -oddsrisk- program,you'llhave "prevalence ratios", not relative risks.Best, -p ________________________________________________ Paul F. Visintainer, PhD Baystate Medical Center Division of Academic Affairs - 3rd Floor Springfield, MA 01199 -----Original Message-----From: owner-statalist@hsphsun2.harvard.edu[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Rosie ChenSent: Thursday, April 08, 2010 2:48 PM To: statalist@hsphsun2.harvard.edu Subject: st: Odds ratio Hello, dear all,I have a question regarding a reviewer's comment on my use of oddsratio ininterpreting the results of a logistic regression, and wouldappreciate it verymuch if you can provide any insight or any references for respondingto thecomment.The reviewer commented that all results are expressed in terms ofodds ratios which makes it very difficult to assess the magnitude of the effect.Probabilities and changes in probabilities would be much easier tointerpret. Myimpression is that, although it is true that predicted probabilitiesmight beeasier to understand, odds ratios have been used extensively inresearch when weinterpret results from logit models.Do you have any suggestions regarding how to respond to this comment,or doyou have any statistics textbooks in your mind that recommend oddsratio as astandard approach reporting results from logistic models?Thank you very much in advance! Rosie* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

-- Michael I. Lichter, Ph.D. <mlichter@buffalo.edu> Research Assistant Professor & NRSA Fellow UB Department of Family Medicine / Primary Care Research Institute UB Clinical Center, 462 Grider Street, Buffalo, NY 14215 Office: CC 126 / Phone: 716-898-4751 / FAX: 716-898-3536 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: RE: Odds ratio***From:*jhilbe@aol.com

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