What are good books that are about video game business models?

Well basically I'm doing an essay on business and management and I'm interested in video games So I'm going write my essay about video game business models like (free to play/pay to play) but i can't seem to be able to find any books on it. Help please?What are good books that are about video game business models?Here's a list on Wikipedia : http://en.wikipedia.org/wiki/List_of_boo鈥?/a>What are good books that are about video game business models?who says ANY books have ever been written on that subject?