[R] survdiff for left-truncated data?
Terry Therneau
therneau at mayo.edu
Tue Aug 4 17:46:53 CEST 2009
> Does anyone know if there is a function like survdiff which can also handle
> left-truncated and right-censored data? When I use it on left-truncated and
> right-censored data I get an error message saying Right censored data only.
coxph(Surv(time1, time2, status) ~ factor(group), data=mydata)
The 'score' test from a Cox model is identical to the logrank test.
(Well, almost identical - if there are two deaths on the same day the LR
calculation uses an n-1 at one point where the Cox uses an n. Neither is
right/wrong, just the choice of the authors of the two different papers. The
difference is never of any consequence, usually several digits out in the test
statistic: just enough to force addendums like this one.)
To recreate the observed -expected columns
fit0 <- coxph(Surv(time1, time2, status) ~ factor(group), data=mydata,
iter=0, na.action=na.exclude)
o.minus.e <- tapply(resid(fit0), mydata$group, sum)
obs <- tapply(mydata$status, mdata$group, sum)
cbind(observed=obs, expected= obs- o.minus.e, "o-e"=o.minus.e)
Terry Therneau
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