@misc{Therneau2012,
author = {Therneau, T.M. and Lumley, T.},
title= {survival: Survival analysis, including penalised likelihood. R package},
year = {2012},
URL = {http://cran.r-project.org/web/packages/survival/index.html},
note = {(Accessed January 16, 2013)},
edition = {2.37-2},
}