[R] hazard ratio of interaction Cox model

From: Giulia Barbati <g.barbati_at_yahoo.com>
Date: Tue, 18 Dec 2007 00:34:43 -0800 (PST)


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.)

# 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



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