epitools (version 0.5-7)

kapmeier: Implements product-limit (Kaplan-Meier) method

Description

Implements product-limit (Kaplan-Meier) method for time-to-event data with censoring.

Usage

kapmeier(time, status)

Arguments

time

numeric vector with individual observation times

status

integer vector indicating status at the end of the observation time: 1 = event, 0 = censored

Value

Details

This function implements the product-limit method for estimating survival probability for time-to-event data with censoring:

    S(t) = product[(nj - dj) / nj] for all tj <= t,="" <="" pre="">
  
  where tj are event times (i.e., times at which one or more events
  occur), nj are the number at risk at time tj (by convention,
  subjects censored at time tj are considered at-risk and included in
  nj), and dj are the number of events at time tj.
  
  A primary purpose of this function was to demonstrate the use of
  available R functions to implement a simple statistical method. For example,
  kapmeier uses sort, order, duplicated,
  tapply, unique, cumprod, cbind, and
  dimnames. Studying this function carefully helps one understand
  and appreciate the utility of R functions to implement simple methods.
  
  For serious survival analysis load the survival package. The
  survfit function in this package implements the product-limit method
  and much more. See examples.

References

Selvin S. Statistical Analysis of Epidemiologic Data (Monographs in Epidemiology and Biostatistics, V. 35). Oxford University Press; 3rd edition (May 1, 2004)

See Also

See also survfit

Examples

##Product-limit method using 'kapmeier' function
tt <- c(1,17,20,9,24,16,2,13,10,3)
ss <- c(1,1,1,1,0,0,0,1,0,1)
round(kapmeier(tt, ss), 3)