This class of objects is returned by the survfit class of functions
to represent a fitted survival curve.
For a multi-state model the object has class c('survfitms', 'survfit').
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.
The following components must be included in a legitimate
survfit or survfitms object.
total number of subjects in each curve.
the time points at which the curve has a step.
the number of subjects at risk at t.
the number of events that occur at time t.
for counting process data only, and only if there was an id
argument, the number of subjects that enter the risk set during the
current interval. If there are event/censoring times at 1, 3, 5 for
instance, someone who enters at time 1 is counted in the (1, 3]
interval, i.e., appears in the row for time 3.
for counting process data only, the number of subjects who exit the risk set, without an event, at time t. (For right censored data, this number can be computed from the successive values of the number at risk).
the estimate of survival at time t+0. This may be a vector or a matrix. The latter occurs when a set of survival curves is created from a single Cox model, in which case there is one column for each covariate set.
a multi-state survival will have the pstate component
instead of surv.
It will be a matrix containing the estimated probability
of each state at each time, one column per state.
for a survival curve this contains standard error of the cumulative hazard or -log(survival), for a multi-state curve it contains the standard error of prev. This difference is a reflection of the fact that each is the natural calculation for that case.
optional. Contains the cumulative hazard for each possible transition.
if there are multiple curves, this component gives the number of
elements of the time vector corresponding to the first curve,
the second curve, and so on.
The names of the elements are labels for the curves.
optional upper confidence limit for the survival curve or pstate
options lower confidence limit for the survival curve or pstate
optional, the starting time for the curve if other than 0
for a multistate object, the distribution of starting
states. If the curve has a strata dimension, this will be a matrix
one row per stratum. The sp0 element has the standard error
of p0, if p0 was estimated.
for survival curves from a fitted model, this contains the covariate values for the curves
the total number of observations that were available
For counting process data, and any time that the
start.time argument was used,
not all may have been used in creating the curve, in which case this value
will be larger than n above.
The print and plot routines in the package do no use this
value, it is for information only.
the approximation used to compute the confidence limits.
the level of the confidence limits, e.g. 90 or 95%.
for multi-state data, the total number of transitions of each type.
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.
an image of the call that produced the object.
type of survival censoring.
optional influence
matrices for the pstate (or surv) and for the
cumhaz estimates.
A list with one element per stratum, each
element of the list is an array indexed by subject, time, state.
the version of the object. Will be missing, 2, or 3
Survfit objects can be subscripted.
This is often used to plot a subset of the curves, for instance.
From the user's point of view the survfit object appears to be
a vector, matrix, or array of curves.
The first dimension is always the underlying number of curves or
``strata'';
for multi-state models the state is always the last dimension.
Predicted curves from a Cox model can have a second dimension
which is the number of different covariate prediction vectors.
The survfit object has evolved over time: when first created
there was no thought of multi-state models for instance. This evolution
has almost entirely been accomplished by the addition of new elements.
One change in survival version 3 is the addition of a survfitconf routine
which will compute confidence intervals for a survfit object.
This allows the computation of CI intervals to be deferred until later,
if desired, rather than making them a permanent part of the object.
Later iterations of the base routines may omit the confidence intervals.
The survfit object starts at the first observation time, but survival
curves are normally plotted from time 0.
A helper routine survfit0 can be used to add this first time point
and align the data.
plot.survfit,
summary.survfit,
print.survfit,
survfit,
survfit0