# survdiff

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##### Test Survival Curve Differences

Tests if there is a difference between two or more survival curves using the $G^\rho$ family of tests, or for a single curve against a known alternative.

Keywords
survival
##### Usage
survdiff(formula, data, subset, na.action, rho=0, timefix=TRUE)
##### Arguments
formula

a formula expression as for other survival models, of the form Surv(time, status) ~ predictors. For a one-sample test, the predictors must consist of a single offset(sp) term, where sp is a vector giving the survival probability of each subject. For a k-sample test, each unique combination of predictors defines a subgroup. A strata term may be used to produce a stratified test. To cause missing values in the predictors to be treated as a separate group, rather than being omitted, use the strata function with its na.group=T argument.

data

an optional data frame in which to interpret the variables occurring in the formula.

subset

expression indicating which subset of the rows of data should be used in the fit. This can be a logical vector (which is replicated to have length equal to the number of observations), a numeric vector indicating which observation numbers are to be included (or excluded if negative), or a character vector of row names to be included. All observations are included by default.

na.action

a missing-data filter function. This is applied to the model.frame after any subset argument has been used. Default is options()$na.action. rho a scalar parameter that controls the type of test. timefix process times through the aeqSurv function to eliminate potential roundoff issues. ##### Value a list with components: n the number of subjects in each group. obs the weighted observed number of events in each group. If there are strata, this will be a matrix with one column per stratum. exp the weighted expected number of events in each group. If there are strata, this will be a matrix with one column per stratum. chisq the chisquare statistic for a test of equality. var the variance matrix of the test. strata optionally, the number of subjects contained in each stratum. ##### METHOD This function implements the G-rho family of Harrington and Fleming (1982), with weights on each death of $S(t)^\rho$, where $S(t)$ is the Kaplan-Meier estimate of survival. With rho = 0 this is the log-rank or Mantel-Haenszel test, and with rho = 1 it is equivalent to the Peto & Peto modification of the Gehan-Wilcoxon test. If the right hand side of the formula consists only of an offset term, then a one sample test is done. To cause missing values in the predictors to be treated as a separate group, rather than being omitted, use the factor function with its exclude argument. ##### References Harrington, D. P. and Fleming, T. R. (1982). A class of rank test procedures for censored survival data. Biometrika 69, 553-566. ##### Aliases • survdiff • print.survdiff ##### Examples # NOT RUN { ## Two-sample test survdiff(Surv(futime, fustat) ~ rx,data=ovarian) ## Stratified 7-sample test survdiff(Surv(time, status) ~ pat.karno + strata(inst), data=lung) ## Expected survival for heart transplant patients based on ## US mortality tables expect <- survexp(futime ~ 1, data=jasa, cohort=FALSE, rmap= list(age=(accept.dt - birth.dt), sex=1, year=accept.dt), ratetable=survexp.us) ## actual survival is much worse (no surprise) survdiff(Surv(jasa$futime, jasa\$fustat) ~ offset(expect))
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Documentation reproduced from package survival, version 3.1-8, License: LGPL (>= 2)

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