Meiping Sun, The Puzzle of Mistaken Millions: The MTA Surcharge and the Surge of Money onto MetroCards. 
Paper, Discussion at the NBER Summer Institute, July 2016.

Fabian Eckert, Mads Hejlesen, and Conor Walsh, The Return to Big City Experience: Evidence from Danish Refugees. 
Paper, Discussion at the NBER Summer Institute, July 2018.