@article{Grambsch1994,
author = {Grambsch, P.M. and Therrneau, T.M.},
title= {Proportional hazards tests and diagnostics based on weighted residuals},
year = {1994},
doi = {10.1093/biomet/81.3.515},
journal = {Biometrika },
volume = {81},
number = {3},
pages = {515--526},
}