Survival Curve Object

Description

This class of objects is returned by the survfit class of functions to represent a fitted survival curve.

Objects of this class have methods for the functions print, summary, plot, points and lines. The print.survfit method does more computation than is typical for a print method and is documented on a separate page.

COMPONENTS

The following components must be included in a legitimate survfit object.

time

the time points at which the curve has a step.

n.risk

the number of subjects at risk at t.

n.event

the number of events that occur at time t.

surv

the estimate of survival at time t+0. This may be a vector or a matrix.

strata

if there are multiple curves, this component gives the number of elements of the time etc. vectors corresponding to the first curve, the second curve, and so on. The names of the elements are labels for the curves.

std.err

the standard error of the cumulative hazard or -log(survival).

upper

upper confidence limit for the survival curve.

lower

lower confidence limit for the survival curve.

conf.type

the approximation used to compute the confidence limits.

conf.int

the level of the confidence limits, e.g. 90 or 95%.

na.action

the returned value from the na.action function, if any. It will be used in the printout of the curve, e.g., the number of observations deleted due to missing values.

call

the call that produced the object.

SUBSCRIPTS

Survfit objects that contain multiple survival curves can be subscripted. This is most often used to plot a subset of the curves. Usually a single subscript will be used. In one particular case – survival curves for multiple covariate values, from a Cox model that includes a strata statement – there is a matrix of curves and 2 subscripts may be used. (In this case summary.survfit will also print the data as a matrix).

See Also

survfit, plot.survfit, summary.survfit, print.survfit.