@unpublished{Abbring2005,
author = {Jaap Abbring and Gerard van den Berg},
title = {Social experiments and instrumental variables with duration outcomes},
year = {2005},
month = {Oct},
volume = {pp.},
doi = {10.1920/wp.ifs.2005.0519},
issn = {1742-0415},
url = {http://www.ifs.org.uk/wps/wp0519.pdf},
}