Surv: Create a Survival Object

Description

Create a survival object, usually used as a response variable in a model formula. Argument matching is special for this function, see Details below.

Usage

Surv(time, time2, event,
    type=c('right', 'left', 'interval', 'counting', 'interval2'),
    origin=0)
is.Surv(x)

Arguments

time

for right censored data, this is the follow up time. For interval data, the first argument is the starting time for the interval.

event

The status indicator, normally 0=alive, 1=dead. Other choices are TRUE/FALSE (TRUE = death) or 1/2 (2=death). For interval censored data, the status indicator is 0=right censored, 1=event at time

time2

ending time of the interval for interval censored  or counting
    process data only.  Intervals are assumed to be open on the left and
    closed on the right, (start, end].  For counting process
    data, event indicates whethe

type

character string specifying the type of censoring. Possible values
    are "right", "left", "counting",
    "interval", or "interval2".  The default is
    "right" or "cou

origin

for counting process data, the hazard function origin.  This option
    was intended to be used in conjunction with a model containing
    time dependent
    strata in order to align the subjects properly when they cross over
    from one strata to anothe

x

any R object.

`Value`

An object of class Surv.  There are methods for print,
  is.na, and subscripting survival objects.   Surv objects
  are implemented as a matrix of 2 or 3 columns.
  In the case of is.Surv, a logical value TRUE if x
  inherits from class "Surv", otherwise an FALSE.

`Details`

Typical usages are
Surv(time, event)
Surv(time, time2, event, type= )
The time,time2 and event arguments are matched by
position, not by name, so use, eg, Surv(time, dead) rather than
Surv(time, event=dead)
In theory it is possible to represent interval censored data without a 
third column containing the explicit status.  Exact, right censored, 
left censored and interval censored observation would be represented as 
intervals of [a,a], (a, infinity), (-infinity,b), and [a,b]  
respectively; each interval is a pair of time points 
within which the event is  
known to have occurred. 
If type="interval2" then the representation given above is 
assumed, with NA taking the place of infinity.  
If type="interval" then event must be given.  
If event is 0, 1, or 2, 
the relevant 
information is assumed to be contained in time,
the value in time2 is ignored,
and the second column of the internal representation contains a 
placeholder value.
Presently, the only methods allowing interval censored data are the 
parametric models computed by survreg and survival curves
computed by survfit; for both of these, 
the distinction between open and closed intervals
is unimportant.  
The distinction is important for counting process data and 
the Cox model. 
The function tries to distinguish between the use of 0/1 and 1/2 coding for 
left and right censored data using 
if (max(status)==2). 
If 1/2 coding is used and all the subjects are censored, it will 
guess wrong.
In any questionable case it is safer to use logical coding,
e.g., Surv(time, status==3) would indicate that a 3 is
the code for an event.
Surv objects can be subscripted either as an object, e.g.
x[1:3] using a single subscript;
in which case the drop argument is ignored;
or as a matrix, using two arguments.
If the second subscript is missing and drop=F
(the default),
the result of the subscripting will be a Surv object, e.g., 
x[1:3,,drop=F],
otherwise the result will be a matrix (or vector), in accordance with
the default behavior for subscripting matrices.

`See Also`

coxph,  
survfit,  
survreg.

`Examples`

Run this codewith(lung, Surv(time, status))
Surv(heart$start, heart$stop, heart$event)
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