R help - Aug 2006 - expected survival from a frailty cox model using survfit

Hello R users

Would somebody know how to estimate survival from a frailty cox model, 
using the function survfit
and the argument newdata ? (or from any other way that could provide 
individual expected survival
with standard error); Is the problem related to how the random term is 
included in newdata ?

kfitm1 <- coxph(Surv(time,status) ~ age + sex + disease + frailty(id, 
dist='gauss'), kidney)
survfit(kfitm1) #ok for mean expected survival

Call: survfit.coxph(object = kfitm1)

      n  events  median 0.95LCL 0.95UCL
     76      58      63      39     132

survfit(kfitm1, newdata=kidney[1,]) #return an error message

Erreur dans x2 %*% coef : arguments inad?quats

Thanks in Advance

-- 
Emmanuel Tillard
Veterinaire
CIRAD-EMVT
Unite de recherche 18

UMR868 Elevage des Ruminants en Regions Chaudes (ERRC)
Campus ENSA-INRA
2 place Viala
34060 Montpellier cedex 1

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