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2008 Dec 04
Comparing survival curves with "survdiff" "strata" help
ExpeRts, I''m trying to compare three survival curves using the function "survdiff" in the survival package. Following is my code and corresponding error message. > survdiff(Surv(st_months, status) ~ strata(BOR), data=mydata) Error in survdiff(Surv(st_months, status) ~ strata(BOR), data = mydata) : No groups to test When I check the "strata" of the variable. I get . . . > strata(BOR) Levels: BOR=PD BOR=PR BOR=SD So I know there are levels associated with the BOR va...