3 IZA Discussion Papers
IZA Discussion Paper No. 11449
IZA Discussion Paper No. 8896
forthcoming in: Oxford Handbook on the Economics of Networks, 2015
IZA Discussion Paper No. 3809
revised version published as 'Proxying for Unobservable Variables with Internet Document-Frequency' in: Journal of the European Economic Association, 2013, 11 (1), 137–165