@article{Heckman2005,
author = {Heckman, J.J.},
title= {The scientific model of causality (with a discussion by M.E. Sobel, 99-133)},
year = {2005},
doi = {10.1111/j.0081-1750.2006.00163.x},
journal = {Sociological Methodology},
volume = {35},
number = {1},
pages = {1--98},
}