My latest research study on addiction and motivations for MMORPG use has been published in the Computers in Human Behavior journal. The link below provides you with access to the research article until June 9, 2015.
Hussain, Z., Williams, G.A. & Griffiths, M.D. (2015). An Exploratory of the Association between Online Gaming Addiction and Enjoyment Motivations for Playing Massively Multiplayer Online Role-Playing Games. Computers in Human Behavior, 50, 221-230.