Cristian Danescu-Niculescu-Mizil Gueorgi Kossinets Jon M. Kleinberg Lillian Lee How opinions are received by online communities: A case study on Amazon.com helpfulness votes http://arxiv.org/abs/0906.3741 2009 CoRR abs/0906.3741 db/journals/corr/corr0906.html#abs-0906-3741 informal publication