@article{Robins1997,
author = {Robins, J.M. and Gill, R.D.},
title= {Non‐response models for the analysis of non‐monotone ignorable missing data},
year = {1997},
doi = {10.1002/(SICI)1097-0258(19970115)16:1<39::AID-SIM535>3.0.CO;2-D},
volume = {16},
number = {1},
pages = {39--56},
}