L. Friedman, and H. Friedman. Working Paper Series, Zicklin School of Business, Baruch College, CUNY; Graduate Center, CUNY CUNY Brooklyn College - Department of Economics, (2008)
N. Archak, A. Ghose, and P. Ipeirotis. KDD '07: Proceedings of the 13th ACM SIGKDD international conference on Knowledge discovery and data mining, page 56-65. New York, NY, USA, ACM, (2007)