[R] Cox regression for prevalence estimates

Thomas Lumley tlumley at u.washington.edu
Tue Sep 7 18:11:04 CEST 2004

robust standard errors are available from coxph with the option


On 6 xxx -1, The Michaelson Institute wrote:

> Hello, I'm an MD working in an eye clinic. I'm learning by myself to use R
> for use in my research works and for implementation in a software project.
> There are some authors who recomends the use of Cox regression as a
> substitute for Logistic regression (<a
> href="http://www.biomedcentral.com/1471-2288/3/21.pdf"> Barros AJD, Hirakata
> VN. BMCMedical Research Methodology, 2003; 3:21 </a>. The use of Cox
> regression permit the estimation of the prevalence rates rather than Odds
> ratios obtained by logistic regression analysis.
> Cox regression is used for time-to-event data. To obtain prevalence rates
> the time has to be constant. One of the problems of Cox regression is that
> the confidence intervals are overestimated. To correct this Barros &
> Hirakata recommend the use of robust variance estimates.
> How can R be used to calculate the prevalence ratios using Cox regression +
> robust variance estimates ?
> Thanks for your collaboration,
> Tomas Karpati MD
> The Michaelson Institute for Rehabilitation of Vision
> Hadassah Medical Organization
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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