L. Nelson, C. Held, P. Pirolli, L. Hong, D. Schiano, and E. Chi. Proceedings of the 27th international conference on Human factors in computing systems, page 1795--1798. New York, NY, USA, ACM, (2009)
S. Ahern, M. Naaman, R. Nair, and J. Yang. JCDL '07: Proceedings of the 7th ACM/IEEE-CS joint conference on Digital libraries, page 1-10. New York, NY, USA, ACM, (2007)