@article{Laird1981,
author = {Laird, N. and Olivier, D.},
title= {Covariance Analysis of Censored Survival Data Using Log-linear Analysis Techniques},
year = {1981},
doi = {10.2307/2287816},
journal = {Journal of the American Statistical Association},
volume = {76},
number = {374},
pages = {231--240},
}