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From |
"Visintainer, Paul" <Paul.Visintainer@baystatehealth.org> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: RE: Odds ratio |

Date |
Fri, 9 Apr 2010 13:34:47 -0400 |

Rich is correct, as the references he provided show. I just want to note the popularity of the substitution method has much to do with the audience it appeals to. In their brief response to comment on their article, Zhang and Yu state, "The uncertainty surrounding the CI (ie, slightly narrower than it should be in some cases) might be indeed the trade-off between simplicity and precision. Methods that can produce more precise estimates, yet are user-friendly, would be ideal." (JAMA, August 11, 1999; vol.282, p529.) The "user" they refer to in "user-friendly" is likely to comprise those who see the CI as nothing more than a surrogate measure of the p-value. Much of that audience -- many of them professional researchers -- would likely find this discussion quaintly academic, and would gladly trade a little "precision" for simplicity. It's simplicity and ease of presenting it to some audiences are the reasons I have used it in the past. I think we can expect this approach to be with us for quite some time. -p _______________________________________________ Paul F. Visintainer, PhD Baystate Medical Center Springfield, MA 01199 -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of jhilbe@aol.com Sent: Friday, April 09, 2010 12:44 PM To: statalist@hsphsun2.harvard.edu Subject: st: RE: Odds ratio I agree with Rich regarding the bias that can be produced in using oddsrisk. There are some situations for which it is acceptable, but mostly it is not. I wrote the command to provide it for those who wanted to use it - not to advocate its use. The method was proposed in an article by Zhang and Yu in 1998 in JAMA -- Journal of the American Medical Association, presumably one of the most elite of medical journals. So it gained considerable popularity. I discuss the method in some length in my book "Logistic Regression Models", pointing out its problems,but also when it can be used. I also offer general guidelines of when it is acceptable to use a risk-probability interpretation for odds ratios, and provide 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 in probability, I recommend looking at Scott Long's -spostado- (-findit spostado-) 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. For example, if you did a survey, and 60% of one group answered a question positively, while 90% of another group answered it positively, your OR would be 6.0. This can be quite confusing for someone trying to interpret this OR like a relative risk. > > One approach might be to try a program by Joseph Hilbe, called -oddsrisk-. It will convert ORs from a logistic regression to a relative risk with 95%CIs. In the 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. If your logistic model was developed on a survey (e.g., cross-sectional), then your ORs are prevalence ORs. If you convert them using the -oddsrisk- program, you'll have "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 Chen > Sent: 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 odds ratio in interpreting the results of a logistic regression, and would appreciate it very much if you can provide any insight or any references for responding to the comment. > > The reviewer commented that all results are expressed in terms of odds ratios which makes it very difficult to assess the magnitude of the effect. Probabilities and changes in probabilities would be much easier to interpret. My impression is that, although it is true that predicted probabilities might be easier to understand, odds ratios have been used extensively in research when we interpret results from logit models. > Do you have any suggestions regarding how to respond to this comment, or do you have any statistics textbooks in your mind that recommend odds ratio as a standard 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/ ---------------------------------------------------------------------- CONFIDENTIALITY NOTICE: This email communication and any attachments may contain confidential and privileged information for the use of the designated recipients named above. 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**References**:**st: RE: Odds ratio***From:*jhilbe@aol.com

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