@inbook{Heckman1981,
author = {Heckman, J.J.},
title= {The incidental parameters problem and the problem of initial conditions in estimating a discrete time - discrete data stochastic process},
year = {1981},
editor = {Manski, C.F.},
editor = {McFadden, D.},
booktitle = {Structural analysis of discrete data with econometric applications},
address = {Cambridge},
publisher = {MIT Press},
pages = {114--178},
}