@article{Rassen2009,
author = {Rassen, J.A. and Brookhart, M.A. and Glynn, R.J. and Mittleman, M.A. and Schneeweiss, S.},
title= {Instrumental variables I: Instrumental variables exploit natural variation in nonexperimental data to estimate causal relationships},
year = {2009},
doi = {10.1016/j.jclinepi.2008.12.005},
journal = {Journal of Clinical Epidemiology},
volume = {62},
number = {12},
pages = {1226−1232},
}