Message-ID: <4767BFEE.3030000@vanderbilt.edu>
Date: 2007-12-18T12:41:18Z
From: Frank E Harrell Jr
Subject: hazard ratio of interaction Cox model
In-Reply-To: <74404.16205.qm@web45614.mail.sp1.yahoo.com>
Giulia Barbati wrote:
> Dear Forum,
> I have a question about interaction estimate in the Cox model:
> why the hazard ratio of the interaction is not produced in the summary of the model?
> (Instead, the estimate of the coefficient is given in the print of the model.)
The 'hazard ratio of the interaction' is not well defined. Decide what
hazard ratio you want to estimate, then ask summary to compute that, e.g.
summary(modINT, XX_PR=c(1,3), XX_DISF=2)
will estimate the 3:1 XX_PR hazard ratio at XX_DISF=2
Frank Harrell
>
>
> # Example:
>
> modINT <-cph( Surv(T_BASE, T_FIN,STATUS)~ NYHA + ASINI + RFP + FE_REC + XX_PR*XX_DISF)
>
> print(modINT)
>
>
> coef se(coef) z p
> NYHA=2 1.254 0.584 2.15 0.031767
> ASINI 0.665 0.409 1.62 0.104247
> RFP=2 0.725 0.704 1.03 0.302578
> FE_REC=2 -1.637 0.810 -2.02 0.043331
> XX_PR 2.189 0.649 3.37 0.000748
> XX_DISF 3.233 1.000 3.23 0.001222
> XX_PR * XX_DISF -2.852 1.280 -2.23 0.025852
>
> summary(modINT)
>
> Effects Response : Surv(T_BASE, T_FIN, STATUS)
>
> Factor Low High Diff. Effect S.E. Lower 0.95 Upper 0.95
> ASINI 2.0725 2.85 0.7775 0.52 0.32 -0.11 1.14
> Hazard Ratio 2.0725 2.85 0.7775 1.68 NA 0.90 3.13
> XX_PR 0.0000 1.00 1.0000 2.19 0.65 0.92 3.46
> Hazard Ratio 0.0000 1.00 1.0000 8.92 NA 2.50 31.86
> XX_DISF 0.0000 1.00 1.0000 3.23 1.00 1.27 5.19
> Hazard Ratio 0.0000 1.00 1.0000 25.35 NA 3.57 179.88
> NYHA - 2:1 1.0000 2.00 NA 1.25 0.58 0.11 2.40
> Hazard Ratio 1.0000 2.00 NA 3.50 NA 1.12 11.00
> RFP - 2:1 1.0000 2.00 NA 0.73 0.70 -0.65 2.10
> Hazard Ratio 1.0000 2.00 NA 2.07 NA 0.52 8.20
> FE_REC - 2:1 1.0000 2.00 NA -1.64 0.81 -3.23 -0.05
> Hazard Ratio 1.0000 2.00 NA 0.19 NA 0.04 0.95
>
> Adjusted to: XX_PR=0 XX_DISF=0
>
>
>
>
> ____________________________________________________________________________________
> Be a better friend, newshound, and
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University