Surv                package:survival                R Documentation

_C_r_e_a_t_e _a _S_u_r_v_i_v_a_l _O_b_j_e_c_t

_D_e_s_c_r_i_p_t_i_o_n:

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

_U_s_a_g_e:

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

_A_r_g_u_m_e_n_t_s:

    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', 2=left censored, 3=interval
          censored. Although unusual, the event indicator can be
          omitted, in which case all subjects are assumed to have an
          event. 

   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 whether an event
          occurred at the end of the interval. 

    type: character string specifying the type of censoring. Possible
          values are '"right"', '"left"', '"counting"', '"interval"',
          or '"interval2"'.  The default is '"right"' or '"counting"'
          depending on whether the 'time2' argument is absent or
          present, respectively. 

  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
          another, but it has rarely proven useful.

       x: any R object. 

_D_e_t_a_i_l_s:

     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.

_V_a_l_u_e:

     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'.

_S_e_e _A_l_s_o:

     'coxph',   'survfit',   'survreg'.

_E_x_a_m_p_l_e_s:

     with(lung, Surv(time, status))
     Surv(heart$start, heart$stop, heart$event) 

