This class of objects is returned by the `survexp`

class of functions
to represent a fitted survival curve.

Objects of this class have methods for `summary`

, and inherit
the `print`

, `plot`

, `points`

and `lines`

methods from `survfit`

.

surv

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

n.risk

the number of subjects who contribute at this time.

time

the time points at which the curve has a step.

std.err

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

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.

method

the estimation method used. One of "Ederer", "Hakulinen", or "conditional".

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

an image of the call that produced the object.

The following components must be included in a legitimate
`survfit`

object.

Survexp objects that contain multiple survival curves can be subscripted. This is most often used to plot a subset of the curves.

In expected survival each subject from the data set is matched to a
hypothetical person from the parent population, matched on the
characteristics of the parent population.
The number at risk printed here is the number of those hypothetical
subject who are still part of the calculation.
In particular, for the Ederer method all hypotheticals are retained for
all time, so `n.risk`

will be a constant.