D. Abrams, R. Baecker, und M. Chignell. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, Seite 41--48. New York, NY, USA, ACM Press/Addison-Wesley Publishing Co., (1998)
Y. Ahn, S. Han, H. Kwak, S. Moon, und H. Jeong. WWW '07: Proceedings of the 16th international conference on World Wide Web, Seite 835--844. New York, NY, USA, ACM, (2007)