http://online.liebertpub.com/doi/abs/10.1089/cpb.2006.9.772

Nick Yee. CyberPsychology & Behavior. December 2006, 9(6): 772-775. doi:10.1089/cpb.2006.9.772.

An empirical model of player motivations in online games provides the foundation to understand and assess how players differ from one another and how motivations of play relate to age, gender, usage patterns, and in-game behaviors.