@article{Keiding1997,
author = {Keiding, N. and Andersen, P.K. and Klein, J.P.},
title= {The role of frailty models and accelerated failure time models in describing heterogeneity due to omitted covariates},
year = {1997},
journal = {Statistics in Medicine},
volume = {16},
number = {2},
pages = {215--224},
}