survsum: Kaplan-Meier Survival Curve and Percentages at Selected Times

Description

Calculates Kaplan-Meier survival percentages, standard error, and number at risk at specified times for defined groups. Test for difference between survival curves.

Usage

survsum(formula, data=sys.parent(), sptms=NULL, xlim, 
tlines=T, log=F, xscale=1,yscale=100, mark.time=F, mark=3, 
cex=1, xlab="Time", ylab="Survival (%)", lgd="bl",
ttl="K-M Survival",...)

Arguments

formula

a formula expression as for other survival models, of the form Surv(time, status) ~ predictors. Same formula expression as used in survfit. See help file for survfit. Maximum of 6 groups.

data

a data.frame in which to interpret the variables named in the formula.

sptms

a specified vector of positive times at which to compute the survival percentages, standard errors, and numbers at risk. A maximum of four times can be specified.

xlim

a vector of the form: c(x1,x2). The approximate minimum and maximum values to be put on x-axis. Default sets x1=0 and x2=maximum time value.

tlines

a logical value indicating whether vertical lines and labels should be drawn on the plot at the specified times.

log

logical value: should the y axis be on a log scale?

xscale

a scalar to be used to divide the x axis. A value of 365, for instance, would be used to convert from days to years.

yscale

a scalar to be used to multiply the y axis. The default value of 100 is used to get a percent scale. yscale=1 would set the y axis from 0 to 1.

mark.time

controls the labeling of the curves. If set to True then curves are marked at each censoring time. If mark.time is a numeric vector, then curves are marked at these specified time points.

mark

vector of mark parameters, which will be used to label the curves. The lines help file contains examples of the possible marks. The vector is reused cyclically if it is shorter than the number of curves.

cex

parameter available to change the size of mark. Not a vector; all marks have the same size.

xlab

character string label for the x axis.

ylab

character string label for the y axis.

lgd

legend placement. "tr"=top right corner of the plot, "under"=under the plot, "n" omits the legend. The default is: "bl"=bottom left corner of the plot.

ttl

title to be printed in the center top.

...

In addition, the high-level graphics arguments described under par and the arguments to title may be supplied to this function.

Value

A list of class "htest", containing the following components:
no.ptsthe total number of data points in each group.
no.eventsthe total number of events in each group.
chisqthe chisquare statistic for the test of a difference between survival curves.
pthe p-value for the above test.
t1a matrix containing the survival percentages, standard errors, and numbers at risk for all groups at time t1.
t2,t3,t4see above.

Side Effects

A plot with multiple survival curves is drawn (one for each group). This plot includes: overall group statistics and group statistics at each specified time point and a test for a difference between survival curves.

Details

The total number of points and events is reported for each group. For each specified time point, group survival percentages (followed by standard error and number left at risk) are computed.

The test for a difference between survival curves uses the chisquare statistic from the survdiff function with rho=0. This is the log-rank test.