dear all


Can you please throw some light on this .I am getting som error when I use


library(survival)
model <- survreg(Surv(time, status) ~ rx + cluster(litter), rats)


Error in rowsum.default(resid(fit, "dfbeta"), cluster) :
'x' must be numeric

Why does it throw up error ?


Thanks and Regards
Sayan Dasgupta

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